# Measuring coffee with a refractometer for beginners



## risky

If, like me, you see TDS/EY as some weird 'voodoo' or you raise your pitchfork and cry 'burn the witch' at the sight of a refractometer then the latest Barista Hustle (and the following ones) will hopefully be of use.

So says Matt Perger:



> From time to time I present a lecture called 'VST:WTF?'. It's a two hour long foray into the science of measuring coffee with a refractometer. More than a thousand Baristas have sat through it, and now I'd like to share portions of the presentation with you as well. Each week I'll be taking a couple slides from the VST:WTF? lecture and explaining them in detail.


About a 5 minute read, very accessible. I look forward to increasing my knowledge with the articles that follow.

http://www.baristahustle.com/vstwtf-part-1/

http://www.baristahustle.com/vstwtf-part-2/

http://www.baristahustle.com/vstwtf-part-3/


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## robashton

I'm looking forward to hearing how wrong I am about my views on the matter


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## The Systemic Kid

Refractometer provides data - doesn't tell you what coffee tastes like. That said, it's a wonderful but expensive tool that saves a lot of time fine tuning the process of making coffee - especially pour over.

Just refracted a Chemex of El Salvador Finca La Ilusion. This is a powerful coffee with huge mouthfeel even at 19.5-20% extraction yield. Because of that, on taste alone, would be tempted to grind coarser to tone down the mouthfeel in the mistaken belief it's over-extracted which, thanks to the data from the refractometer, I know it isn't.


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## robashton

I always refer to it as being a post-mortem diagnostic tool, certainly helps with making informed decisions - I'd not want to do without it. Given that the variety of beans I use taste good from 19% to 23% on various methods the actual numbers are really only useful as a way of measuring brews against each other on the same bean.


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## risky

I think I need to start saving.


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## jlarkin

The Systemic Kid said:


> Refractometer provides data - doesn't tell you what coffee tastes like. That said, it's a wonderful but expensive tool that saves a lot of time fine tuning the process of making coffee - especially pour over.
> 
> Just refracted a Chemex of El Salvador Finca La Ilusion. This is a powerful coffee with huge mouthfeel even at 19.5-20% extraction yield. Because of that, on taste alone, would be tempted to grind coarser to tone down the mouthfeel in the mistaken belief it's over-extracted which, thanks to the data from the refractometer, I know it isn't.


So did (or would) you change anything or did you decide that it tasted over extracted but wasn't so you left it?


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## The Systemic Kid

For pour over - 19.5-20% is the best balance between body and flavour pofile. So that's what I aim for. With most beans it's pretty clear taste-wise. The Finca Ilusion is a hugely powerful coffee - having the data from the refractometer saves wasting beans.


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## garydyke1

Im a huge fan of low(er) TDS high(er) EY brews.

Brazens at Tilt we aim for 21.5-22% EY . An occasional 23%er surprises us with tastiness .


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## robashton

I go with a "why not both" approach, and tend to sit between 21-22% at 1.5tds, sometimes 1.6tds and 23% ey with spiffing Kenyans because why not.

i did some tests with various non coffee folk and they preferred the "stronger" brews and I got with the program


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## jeebsy

1.3 tds ftw


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## jeebsy

risky said:


> I think I need to start saving.


You can borrow mine for a bit if you want.


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## risky

So preempt next weeks article and explain to me what the relationship is between TDS and EY again?



jeebsy said:


> You can borrow mine for a bit if you want.


May take you up on that kind offer.


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## jeebsy

http://coffeestrides.blogspot.co.uk/2014/06/why-do-we-measure-everything-extraction.html?m=1


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## garydyke1

1.3TDS is about the higher end of our preference . Water being 155PPM and pretty ideal

Its all about the water though. An emergency aeropress with Brum tap water (58PPM) revealed 1.45TDS and it was thin and lifeless


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## MWJB

TDS is is the concentration of the coffee beverage. E.g. a 10%TDS espresso is 10% dissolved coffee, 90% water, so a 40g shot would have 4g of dissolved coffee in it. A 1.5%TDS brewed coffee is 1.5% dissolved coffee, so 200g of brewed coffee at 1.5%TDS would have 3g of dissolved coffee in it.

Think of it like ABV with alcoholic drinks. But like alcoholic drinks, strength is very open to preference. It doesn't tell you much on it's own...unless at extremes, like a 1.5% espresso shot would be unlikely, unless a coffee shot (just like you wouldn't expect a bottle of whisky to be the same ABV as a typical beer).

TDS is mainly used to back calculate EY. EY is the % of the dry dose of coffee that makes it into the cup, whether brewed or espresso, there is rather more commonality here than with respect to strength (both can be good at a factor of x10 in terms of strength), but both may be preferred at the same EY, or in a similar range of EYs. However, there isn't any one right EY, it depends on grind quality & brew method, but a lot of folk find a preference for coffee 2-3% either side of 20% (so 20% of your dose is dissolved into the cup) but not always spanning the whole range of 6% (maybe +/- 1 to 1.5% for a certain preference range?).

Knowing what you have makes it easier to determine how hard you have to push to hit a preference point (usually through grind adjustments), or whether you can hit another point more easily.


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## risky

So for example if you pulled a shot then diluted it, regardless of how much you diluted it the EY would be the same? Because there only ever was so much extracted from the bean in the first place? But the TDS would drop the more you diluted it because there would be more water and less coffee in the cup?


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## jeebsy

risky said:


> So for example if you pulled a shot then diluted it, regardless of how much you diluted it the EY would be the same? Because there only ever was so much extracted from the bean in the first place? But the TDS would drop the more you diluted it because there would be more water and less coffee in the cup?


Yeah, that's right - if you made a brew that 1.6 TDS (ie a bit strong for most preferences) but the EY was in the ballpark you could dilute it to bring the strength down. Weak over/strong under etc was hard to grasp at first. Lots of info here too: http://coffeeforums.co.uk/showthread.php?24895-Questions-on-EY-TDS-etc&p=319323


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## risky

Yes that's a good read that thread!


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## robashton

I do add water to some of my 1.5-1.6 brews thats for sure - I just can't be faffed adjusting my recipes when I encounter a brew that's too much for that


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## matisse

Cat amoungst pigeons time.

1-1.2 tds is where we end up on the regular, and its tastes great


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## garydyke1

matisse said:


> Cat amoungst pigeons time.
> 
> 1-1.2 tds is where we end up on the regular, and its tastes great


That's our happy place too ; )


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## PeterL

risky said:


> So says Matt Perger:
> 
> About a 5 minute read, very accessible. I look forward to increasing my knowledge with the articles that follow.
> 
> http://www.baristahustle.com/vstwtf-part-1/


Interesting, St Ali, they were my local in South Melbourne.

Some of their large batch pour over stuff is stunning, very very very yummy.


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## robashton

I don't see the TDS thing as being controversial - my preference changes week to week and I adjust my recipes to cater for this; that's one of the reasons I learned how to make coffee in the first place after all.

I know that the common person often complains that the 1.2-1.3 stuff is weak - expecting coffee and being given a brew more akin to tea, pumping up the TDS and keeping EY high is an antidote to that and I noticed Prufrock doing it last time I was down there (they served all three filters that I had above 1.4 TDS, the La Cabra Crazy Fruit Kenyan was at 1.5 too and was completely mind boggling) - it certainly changed my attitude to 1.3+ TDS coffee.

My parents definitely prefer the 1.4+ TDS brews (and have a preference for the lower acidity higher chocolate brews), some of the folk that visited Cafe Ashton in Lithuania couldn't get enough of that crazy Kenyan at 1.6 TDS (and I couldn't deal with it above 1.4 - bypass all the way). Pleasures of not running a shop is being able to cater for all tastes easily.

Refrac has at least made it super easy to understand the recipes needed to create stronger brews whilst keeping EY at target levels per bean, yay the refrac.


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## robashton

Interestingly I'm sat at Brew Lab right now and the filter they just served me is at 1.46 TDS, it tastes more like a 1.3, presumably this is down to the water.


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## fluffles

robashton said:


> I don't see the TDS thing as being controversial - my preference changes week to week and I adjust my recipes to cater for this; that's one of the reasons I learned how to make coffee in the first place after all.
> 
> I know that the common person often complains that the 1.2-1.3 stuff is weak - expecting coffee and being given a brew more akin to tea, pumping up the TDS and keeping EY high is an antidote to that and I noticed Prufrock doing it last time I was down there (they served all three filters that I had above 1.4 TDS, the La Cabra Crazy Fruit Kenyan was at 1.5 too and was completely mind boggling) - it certainly changed my attitude to 1.3+ TDS coffee.
> 
> My parents definitely prefer the 1.4+ TDS brews (and have a preference for the lower acidity higher chocolate brews), some of the folk that visited Cafe Ashton in Lithuania couldn't get enough of that crazy Kenyan at 1.6 TDS (and I couldn't deal with it above 1.4 - bypass all the way). Pleasures of not running a shop is being able to cater for all tastes easily.
> 
> Refrac has at least made it super easy to understand the recipes needed to create stronger brews whilst keeping EY at target levels per bean, yay the refrac.


Assuming you're brewing at 60g/L via your Lido3, that's quite a different experience for me. I generally find (with the odd exception) EY's over 20.5% don't taste good - they start getting drying and what I would describe as over-extracted. Perhaps the different water plays a big part here, I believe Chris Hendon has some further research on this to be published at some point (some water tasting better at lower EY)


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## robashton

What you extract is as important as how much you extract* - if I want a lido3 brew to taste good above 20.5/21% it needs to come through in less than 2m30s - any longer than that and gets weird fast. It is actually the odd exception that goes to 23% (literally the occasional kenyan) - most brews are 20.5-21% with a TDS of 1.4 with a your standard 60g/l v60 brew.

*Seems obvious, but with constant focus on EY it's often overlooked


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## MWJB

robashton said:


> What you extract is as important as how much you extract* - if I want a lido3 brew to taste good above 20.5/21% it needs to come through in less than 2m30s - any longer than that and gets weird fast. It is actually the odd exception that goes to 23% (literally the occasional kenyan) - most brews are 20.5-21% with a TDS of 1.4 with a your standard 60g/l v60 brew.


12g:200?


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## robashton

MWJB said:


> 12g:200?


Nah, 15g/250g, I could never get the hang of the 200g recipes for some reason (entirely user error of course)


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## risky

Part 2 now up:

http://www.baristahustle.com/vstwtf-part-2/


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## jlarkin

Bit of a slow burn these VST hustles


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## robashton

On this subject and something on topic to how I do things


__
http://instagr.am/p/_ee0upyuCj/


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## MWJB

You can't stir, cool, or let espresso settle to get an accurate reading of TDS. Espresso and all metal filtered/unfiltered coffee includes non dissolved solids which throw out the reading. A refractometer is expecting you to put a filtered solution on the prism. Atago clearly state that you should expect deviations of up to 0.5%TDS if reading unfiltered espresso (they don't provide a filtration method for the PAL coffee). They clearly expect and explicitly state an expected margin of error. The native scale for the Atago is BRIX (sugar solution, no solids), it can't compensate.

When an extraction yield method was described by EE Lockhart it was stipulated that coffee should be filtered, repeatedly if necessary, to remove undissolved solids. EY measurement has always pertained to dissolved solids, those that are dissolved in solution, rather than undissolved solids in suspension. Socratic's chemistry advisor doesn't seem to grasp this...which is a little worrying.

Socratic have never tested the effect of filtration against a datum for dehydration results, they are simply seeing what happens when you put a contaminated sample on the prism of a refractometer.


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## jeebsy

Do you think it will be over by a consistent amount each time, so will know what to deduct to get an equivalent filtered value?

If it's not consistent, how could you do an EY calculation off an unfiltered sample? You couldn't use the unfiltered result as it would give a false reading.


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## aaroncornish

risky said:


> I think I need to start saving.


Me too!! Seem to be stumbling further and further into the world of brewed


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## risky

@MWJB for anyone querying on the Instagram we are being directed to read their previous article here:

http://socraticcoffee.com/2015/07/measuring-total-dissolved-solids-a-refractometer-comparison-part-iii-espresso-filters/

What you're saying makes sense to me. I'm not sure how they go from 'refrac is complex' to 'don't use filters'.


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## robashton

I have gained shed loads of value without filters for spro, and definitely gained more value than not having done it through fear of expense or incorrect results (this would be the important point here)

I get consistent and meaningful results through consistent prep and it's very easy to see changes when adjusting a recipe, I don't get why you'd care about the actual number unless you were communicating with somebody who needed to know the actual number for whatever reason - what matters is change and finding peaks.


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## Mrboots2u

How would this match up against quality being " objective " .

If you are posting or blogging that this coffee is great at X EY , or should be hitting targets of X , how would the reader know if it's the same process used to measure it as other people using a vs. There would be an assumption that you use a standard vst protocol to do is otherwise ( filter) .

Or are your posted measurement filtered ?


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## MWJB

robashton said:


> I get consistent and meaningful results through consistent prep and it's very easy to see changes when adjusting a recipe, I don't get why you'd care about the actual number unless you were communicating with somebody who needed to know the actual number for whatever reason - what matters is change and finding peaks.


You number could be >1.5%EY different to people doing it properly, that's enough to produce a significant difference in the cup & means targets you quote will be out of whack with anyone repeating what you do.

Buying a refractometer seems a very expensive way of conducting a "finger in the air" test, when for the cost of a filter you get a result you can share with other users with confidence. If you're not filtering, you are not measuring TDS, nor EY.

How are you determining that your readings are "consistent"?


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## GlennV

Whether or not a 0.45micron syringe filter removes material that can be regarded as "extracted" is not really the point here. What matters is that refractometers simply don't work as well on the unfiltered media (although they might work "well enough"). This is immediately apparent if you look at filtered and unfiltered espresso through an optical refractometer - when filtered you get a sharp and unambiguous shadow line, when not you get a blurred one which you have to interpret in some way. This is well understood when using refractometers to measure coolant concentrations when contaminated by oil: eg http://www.zebraskimmers.com/oil_skimmer_products/refractometers.html

What VST claim is that if you put espresso through a 0.45micron filter then the results from their refractometer will match those obtained from dehydration of the same filtered sample, within the stated accuracy. It may well be the case that you can get good enough accuracy by following a consistent protocol that doesn't involve filtering, but there are no guarantees.


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## robashton

Meh, I'm not having a cock waggling argument about this one - my method works, I don't give a shit what you all think.

my posted measurements are with filters.


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## Mrboots2u

I thought They were Reasonable questions Rob - and I genuinely wanted an answer .


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## MWJB

risky said:


> @MWJB for anyone querying on the Instagram we are being directed to read their previous article here:
> 
> http://socraticcoffee.com/2015/07/measuring-total-dissolved-solids-a-refractometer-comparison-part-iii-espresso-filters/
> 
> What you're saying makes sense to me. I'm not sure how they go from 'refrac is complex' to 'don't use filters'.


They have gone from saying that filters don't affect the readings for the Atago* (which even Atago don't corroborate), to saying they do? Does this mean they are pulling the linked test report from the main site?

(*though I don't know how they came to this conclusion, as the shots they pulled for the filtered tests were not the same shots measured for the unfiltered tests, and the filtered shots themselves varied in TDS by orders of magnitude greater than the standard deviation. The averaged standard deviation for Atago with filter vs without filter, over 6 tests, was significantly different to p=.001. Prior to the test being published they published incomplete data on their Instagram account, which was naturally misinterpreted by H-B readers & to his credit Jeremy did ask commentators to wait until full results were published. But full results seem few & far between these days.)

Let me get this right, they zero a £10,000 bench top refractometer (so, we'll assume they can afford filters) with air, then with DI water (another conflicting result with previous "test"), then slap a contaminated sample on it?

But anyway, we're getting off topic...the Barista Hustle article makes no mention of Atago & Perger knows how to take a sample properly.


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## AndyS

robashton said:


> On this subject and something on topic to how I do things
> 
> 
> __
> http://instagr.am/p/_ee0upyuCj/





jeebsy said:


> Do you think it will be over by a consistent amount each time, so will know what to deduct to get an equivalent filtered value?
> 
> If it's not consistent, how could you do an EY calculation off an unfiltered sample? You couldn't use the unfiltered result as it would give a false reading.


I've done dozens and dozens of direct filtered vs unfiltered espresso readings with a VST LAB instrument. Originally it appeared that I could just subtract some fraction of a percent from the unfiltered reading to arrive at a reliable value. But the more I've done it, the more outliers I've found. It became clear to me that even with consistent prep, unfiltered samples are simply unreliable; there is no consistent subtraction factor one can use to convert an unfiltered result into a filtered one. That was disappointing, because the filters are expensive, but that's the reality for me.

Because of this, I think it's misleading to publish refractometer results from unfiltered samples. It's OK to fool around with unfiltered stuff for personal use, sure, but posting unfiltered results on the web is a dubious practice, IMHO.

I haven't followed what the Socratic guys have done, because once they claimed that an Atago had the magic ability to ignore suspended solids and give you a correct reading, I didn't trust them. It doesn't matter how many complex statistical analyses they post, or how much money they claim to be saving you, or how many people post how they are heroes. "Buyer beware."


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## risky

So what's their agenda then? Because they claim to be independent.

Andy or Mark have you ever contacted them about this?


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## AndyS

risky said:


> So what's their agenda then? Because they claim to be independent.
> 
> Andy or Mark have you ever contacted them about this?


I'm not saying they are not independent, I have no idea. I suppose their agenda is like most everyone else's: do interesting experiments, satisfy their own curiosity, shatter a few myths, gather the praise of their peers, get lots of hits to their website, attract some money, become famous, get pretty girls to sleep with them....

Wouldn't you say that good science is at odds with the desire for fame? Good science is very tedious and conservative. It certainly isn't done via teasers posted on Instagram. It isn't done on forums like this one, either.

I distinctly remember the bogus announcements of "cold fusion" back in 1989. They were hastily made via news conference rather than by scientific journal. The idea was to get credit and to get lots of funding. It seemed like the wrong way to do science then and still does now. But that's par for the course in our modern world of instant communication.

BTW I'm certainly not saying I'm above all this. I try to be careful, but the stuff I've posted on forums is very opinionated, not necessarily "good science."


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## MWJB

risky said:


> So what's their agenda then? Because they claim to be independent.
> 
> Andy or Mark have you ever contacted them about this?


Yes.


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## risky

Dare I ask what the response was? (If there was one)


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## MWJB

They carry on regardless, ignoring existing conventions. Which I am not saying is bad in itself, I think it's good to challenge conventions & rethink ideas. But first you have to understand the convention being presented & how it was arrived at before trying to present perceived criticisms, or alternatives. When you do present, it should be done clearly & transparently, accepting you are going to obviously have to receive & consider other views.

We all only learn by accepting there is stuff we don't know, they are claiming to know things without an explanation as to how they arrived at this knowledge.


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## risky

Meanwhile Mr. Perger shares part 3. And I think it's all starting to click for me,

http://www.baristahustle.com/vstwtf-part-3/

The point about a brew ratio restricting you to a line was something I hadn't even considered before.


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## Brewster

Does anyone know where to source the Atago Coffee TDS refractometer from in the UK - I can see them for £180 but shipped from Japan and I suspect will attract tax etc?

I see that absolute accuracy might be worse than the VST, but at under a third of the price might be worth looking at...?


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## fluffles

For home use I would think they're the most sensible choice, unless you have 500 quid burning a hole in your pocket


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## Mrboots2u

fluffles said:


> For home use I would think they're the most sensible choice, unless you have 500 quid burning a hole in your pocket


Sensible coz they are cheaper ?

If you use a vst with filters for espresso you will get a different reading to an atago without filters ( same sample )

I've tried .

Problem is as Andy also point out that unfiltered samples on a vst are not always consistent - ie take 0.2-3 off for a non filtered sample . You get random spikes that don't correspond.

I'm not convinced by the unfiltered readings on an atago . But I'm not basing this on a massive scientific sample - it's really is a pocket science opinion so Pays your money take your chances. I really am not an expert on this .

It could help you ascertain if a number goes up or down what happens to taste ( as rob indicates ) .


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## GlennV

I really don't understand why some people here are so down on the socratic coffee guys. The instagram stuff is a bit sensationalist (though no more so than many others commentators) but their reports on the website are open and transparent, and they release all their data. I do have a few technical queries, but they say exactly what they have done, and their experimental design and analysis conforms to the usual norms. Finally, refractometry for colloidal dispersions (such as espresso) remains an active area of research, and the question of filtering vs not filtering is certainly not cut and dried. For now I'm happy to use my VST Lab II refractometer and (cheap, from ebay) syringe filters, but I don't think there's any doubt that in doing so stuff is being removed simply in order to make the measurement easier.


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## MWJB

Brewster said:


> Does anyone know where to source the Atago Coffee TDS refractometer from in the UK - I can see them for £180 but shipped from Japan and I suspect will attract tax etc?
> 
> I see that absolute accuracy might be worse than the VST, but at under a third of the price might be worth looking at...?


They're not a third of the price of a VST, they're nearly £400 with calibration. That's too much to spend for the drop in precision, compared to VST IMO, the margins add up quickly & relate to quite a different reading at the end of the day. You still need the VST software & filters for metal filtered/unfiltered coffee. It's going to cost you either way, I'd prefer to have the higher spec device.


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## MWJB

GlennV said:


> I really don't understand why some people here are so down on the socratic coffee guys. The instagram stuff is a bit sensationalist (though no more so than many others commentators) but their reports on the website are open and transparent, and they release all their data. I do have a few technical queries, but they say exactly what they have done, and their experimental design and analysis conforms to the usual norms. Finally, refractometry for colloidal dispersions (such as espresso) remains an active area of research, and the question of filtering vs not filtering is certainly not cut and dried. For now I'm happy to use my VST Lab II refractometer and (cheap, from ebay) syringe filters, but I don't think there's any doubt that in doing so stuff is being removed simply in order to make the measurement easier.


The linked Instagram post directly contradicts the espresso filter test findings for the Atago that they published. It's a 180deg u-turn. Which one is right? "Right hand, come in right hand...this is left hand calling..."

They only release data for the articles published on the main blog, not the Instagram account.


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## GlennV

MWJB said:


> The linked Instagram post directly contradicts the espresso filter test findings for the Atago that they published. It's a 180deg u-turn. Which one is right? "Right hand, come in right hand...this is left hand calling..."
> 
> They only release data for the articles published on the main blog, not the Instagram account.


Yes, the instagram stuff is a bit sensationalist, as I said. As for the report, there's nothing in it to be contradicted. They did an experiment and found no significant effect. Perhaps they've now done a more powerful experiment? I don't know, but I do look forward to seeing the full results. No, this is not really the way science should be reported - but it is entertaining.


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## aaroncornish

So my VST has arrived from Canada. Looking forward to having a crack at this at the weekend.


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## jeebsy

aaroncornish said:


> So my VST has arrived from Canada. Looking forward to having a crack at this at the weekend.


Any extra charges?


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## aaroncornish

Cost me £350 all in.


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## risky

@MWJB interesting one coming up:



> The purpose of this experiment will be for testing the impact of the syringe filters and robustness of the refractometer detector schemes by using/creating four solutions:
> 
> ⚪distilled water
> 
> ⭕sucrose
> 
> ⚫instant coffee
> 
> ��brewed coffee.
> 
> Each solution will be broken into 8 containers, with increasing amounts of TiO2 added.The scientific analysing and the write up of this experiment will be published on www.socraticcoffee.com





GlennV said:


> For now I'm happy to use my VST Lab II refractometer and (cheap, from ebay) syringe filters, but I don't think there's any doubt that in doing so stuff is being removed simply in order to make the measurement easier.


Out of interest, why did you sell yours?


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## risky

aaroncornish said:


> Cost me £350 all in.


Hold on, wait, what, was this new? Version III?


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## MWJB

Not interesting at all. Mumbo jumbo.

You test the efficacy of refractometers readings of TDS against the datum of dehydration, which is how the coffee scale was developed.

How does TiO2 taste in coffee anyway? ;-)


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## GlennV

risky said:


> Hold on, wait, what, was this new? Version III?


Secondhand, advertised on HB I believe.


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## aaroncornish

GlennV said:


> Secondhand, advertised on HB I believe.


Yeah it was









A version II


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## aaroncornish

Let numberwang commence


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## jeebsy

Typo! Arrgh


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## aaroncornish

Quick question, sorry if it has been asked before, how does VST take into account the TDS of water used to make the brew?

The guides suggest to zero the VST with distilled water, which is obviously not what is used to make actual drink.


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## Mrboots2u

aaroncornish said:


> Quick question, sorry if it has been asked before, how does VST take into account the TDS of water used to make the brew?
> 
> The guides suggest to zero the VST with distilled water, which is obviously not what is used to make actual drink.


All you need to do is calibrate to with distilled

the vst read what it reads - different water used will give you different extractions and yields but as long as your calibration is the same as everyone elses the reading is accurate ....


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## jlarkin

the TDS of the water is also, as far as I understand such a minimal amount compared to the actual end brew that it's going to have a very small effect on the reading that comes out. I think it was described as a gnats naughty bits of difference, by Mr. Perger.


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## MWJB

Also the refractive index of distilled water is known, so you're zeroing to a datum. This is normal practice.


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## aaroncornish

Cheers guys. I am clearly overthinking it.

Just seemed that there should be another step, zero with distilled, test water, then test sample.

My water here has a very very low TDS, where as someone down south might very hard.

I guess though that the hardness of the water would effect the extraction anyway so its a moot point

Aaron


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## aaroncornish

My VST didn't come with a case.

Have ordered a mini Peli case - we use them a lot at work and they are very good (and float)

https://peliproducts.co.uk/products/cases/1120-case-with-foam-blackr1-890.html


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## jlarkin

aaroncornish said:


> My VST didn't come with a case.
> 
> Have ordered a mini Peli case - we use them a lot at work and they are very good (and float)
> 
> https://peliproducts.co.uk/products/cases/1120-case-with-foam-blackr1-890.html


Looks handy, I went with the VST one: http://www.hasbean.co.uk/products/vst-hard-case


----------



## aaroncornish

I saw that one on there, but thought it was a bit steep, when a Peli case is only a couple of quid more


----------



## aaroncornish

So team VST... Help a noob out

I have just pulled a shot, tasted lovely, of the LSOL.










So here we are at the upper end of the extraction target. As I am not lucky enough to have an EK - this is probably too high.

So next step is to bring the extraction down to more like 19-20%

My question Is - what would you do to achieve this result? Grind coarser or up the brew ratio?


----------



## MWJB

Whoa! You said it tasted lovely? Don't overthink or try to second guess your target. The refractometer & software tell you what you have, *you* decide how that relates to your preference. Maybe after measuring & tasting some more you might find your target shifts a little, but don't fret over 0.2 or 0.4%EY differences shot to shot, look at a realistic target as being around +/-1%EY (e.g. 20% +/-1%)?

If you want to bring the EY down a shade, keep the same brew ratio & grind a little coarser.


----------



## aaroncornish

Thanks









It tasted lovely, but could it taste better? Want to try the same coffee at the top, middle and bottom of the range, just to get my head round the taste differences more than anything


----------



## GlennV

No, that's fine. I was pulling the LSOL at around the same numbers (before I sold my refractometer). EY slightly larger if anything.

Edit: I see you're using the default CO2 and moisture parameters. Some people set these to zero, or quote yield/dose*tds, which gives EY around 1% lower. So, be wary of comparing your numbers to what others report unless you know how they're calculating them.


----------



## The Systemic Kid

Pull shots side by side and see how they taste. Refractometer is a great tool for providing data but it doesn't tell you how it will taste.


----------



## aaroncornish

The Systemic Kid said:


> Pull shots side by side and see how they taste. Refractometer is a great tool for providing data but it doesn't tell you how it will taste.


Totally get that, that's what I am trying to do









Was just after opinions/experience/suggestions on the best way to affect extraction consistently. Always mindful that I want to reduce variables changed and do things repeatably in order to avoid numberwang (love that my phone autocorrected numberwang)


----------



## MWJB

GlennV said:


> Edit: I see you're using the default CO2 and moisture parameters. Some people set these to zero, or quote yield/dose*tds, which gives EY around 1% lower. So, be wary of comparing your numbers to what others report unless you know how they're calculating them.


As the software screenshot explicitly states the parameters, we are in no doubt as to what Aaron is seeing, other VST users can therefore make the same corrections and get a comparable reading, if for some reason, they have decided to reset moisture & CO2. Probably best not start out trying to confuse the issue whilst Aaron is finding his feet. Roasted coffee is known to contain moisture & CO2, these are not soluble solids counted towards extraction, but as you say, it is best to stick to parameters & not flit between methods.


----------



## aaroncornish

Thanks everyone. All great advice


----------



## the_partisan

I've finally got hold of a second hand VST II (thanks to this forum), and can't wait to start using it. Any special tips for first time refractometer owners, besides the official manual?


----------



## The Systemic Kid

Get some distilled/ionised water to calibrate before taking readings.


----------



## the_partisan

Do you calibrate everytime, or just once in a while?

I just did my first measurement and it came at 1.25% TDS, at 18.9% extraction for a V60 drip. Quite under my expectations, I always assumed it would be around 20%. The LRR also seems to be much higher than the default in my case (2.5 vs 2.1) but have no idea what would be causing this.

Also, are the transfer pipette reusable or are they meant for single use?

Will grind finer next time and compare.


----------



## Mrboots2u

I calibrated every session as a minimum . If that session went past 10 minutes or so then I'd recalibrate . If you read and use the vst protocols for use then you won't go far wrong .

It's a scientific instrument , use it as the manufacturer suggests.

Did you have your coffee tools set to filter btw.

Again as always use as a measure , push the grind finer if you want to see where the taste goes , but it might be your preference for that coffee is at 19% EY.

For a v60 that brew sounds a little weak for my preference but it might not be for yours


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## MWJB

Calibrate before each session, or if large gaps between measurements, or if you perceive a change in room temp.

If your LRR is consistently 2.5 I wouldn't worry, I always wait until drips essentially cease.

Pipettes supplied are single use, you could use a spoon to transfer brew to cooling vessel, then a pipette from there to refractometer. You could reuse the pipette for DI water only for calibration. You could source other pipettes if you wanted to find a reuseable solution.

Not necessarily anything wrong with 18.9EY, I've had coffees that were great at 18.5% others at 21.5%.


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## the_partisan

The coffee tasted still good, but I drank it after I was faffing around with measurements, so it was pretty much almost at room temp by the time I got to it. I will drink first and measure afterwards next time.

I weigh the pot before the brew, and after the brew and I take the difference as the beverage weight. Using double scales might be another option.

Just curious what makes the pipette single use? Since sterilization isn't so much of an issue here.


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## The Systemic Kid

Don't need to single use pipettes IMO. If you clean them immediately after use by rinsing in tap water, they'll be OK. Just make sure you purge the pipette before drawing a coffee sample to expel any retained water. When immersing the pipette in the brewed coffee, draw up some coffee, expel and repeat several times. Then take a sample you want to refract.


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## MWJB

the_partisan said:


> I weigh the pot before the brew, and after the brew and I take the difference as the beverage weight. Using double scales might be another option.


That's fine, stick to one method for consistency, when using scales under the cup/carafe some creep more than others, so best to do it the same way each time.


----------



## the_partisan

After grinding one notch finer (on electric Wilfa grinder) , the extraction came at 1.4TDS / 21.23%

Pretty substantial difference, but the coffee also tasted much sweeter and better to my preference.

Still not sure if I'm doing everything 100% right, but quite enjoying this so far. I should probably be doing several brews at same setting to see what my variance is next.


----------



## the_partisan

A question - on my last measurement, I took a bit of brew from the coffee to thick bottomed glass, and swirled the liquid to cool it down faster. In the first sample I took, the TDS reading was 1.6, but in the second (and subsequent samples) it was around 1.34-1.35. I wonder what caused first reading to be so high ? The coffee didn't taste overextracted/bitter at all, so my guess is the second one is correct. I am also sometimes seeing a lot of bubbles when emptying the pipette, probably due to my lack of skills, I'm assuming that there shouldn't be any bubbles when measuring?

On another note - I recently switched (due to necessity) from Hario Japanese filters to Dutch filters. In the Japanese filters, I had 1.27TDS/19% extraction on my last brew with a brew time of 3:20, where as with the new papers, using same grind and pour timing, I had 1.35/20%, and the brew took a lot longer than I'm used to. (4+ min in total for 225g of Brew Water). It still tasted great though!


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## MWJB

No idea what caused the big jump in your first reading, never seen anything like that, my readings either stay stable or only change by +/-0.01% over a few reads.

How long are you leaving the sample to cool in the glass? Leave it at least 30sec, then the same again when you drop the sample on the prism.

I found using larger pipettes reduced the incidence of bubbles in the sample, if I get a bubble I use the pipette to suck it back up.


----------



## the_partisan

Do you have a link / pic to the pipettes you use? Or are you talking about the bigger one use pipettes?

I was given some dark roast beans, and even at 1.35 TDS / 20.7% they taste fairly bitter. I seem never be able to get great coffee with dark beans from a V60. Will try to keep going coarser in grind.


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## MWJB

https://www.creamsupplies.co.uk/dropping-pipette-not-sterile-3ml-pack-of-20 ...I transfer from the carafe/cup with a cupping spoon, then just use the pipette to transfer from cooling glass to prism.

Maybe back off the brew ratio for dark roasts to lessen intensity (medium dark might give up some sweetness at a similar, or even higher EY, but you might need to tame the strength), the lighter people roast the higher the strength on the 'ideal' extraction box typically moves. Or, just brew the dark roast in French press, seems easier to get what sweetness there may be, this way. You may struggle to get a very sweet extraction in a V60 with a properly dark roast.


----------



## Step21

Thanks for the timely link to pipettes - I'm running low on them and was wondering where to get a new supply!


----------



## the_partisan

MWJB said:


> https://www.creamsupplies.co.uk/dropping-pipette-not-sterile-3ml-pack-of-20 ...I transfer from the carafe/cup with a cupping spoon, then just use the pipette to transfer from cooling glass to prism.
> 
> Maybe back off the brew ratio for dark roasts to lessen intensity (medium dark might give up some sweetness at a similar, or even higher EY, but you might need to tame the strength), the lighter people roast the higher the strength on the 'ideal' extraction box typically moves. Or, just brew the dark roast in French press, seems easier to get what sweetness there may be, this way. You may struggle to get a very sweet extraction in a V60 with a properly dark roast.


Loosened up the grind two more notches on the feldgrind (2+4) and ended up at 1.28 TDS / 19.5%, which had a more balanced flavour, but still kind of bitter. But I think in general I much prefer lighter roasts which can have a lot of sweetness without any bitterness. Refractometer has been quite useful in finding out what is happening though..


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## the_partisan

How does the TDS of the water effect the TDS of the brew? Since we 0 the refractometer with distilled water, wouldn't using non-distilled water affect the TDS? I measured the TDS of tap water (0.08) and filtered water (0.06), and if they would add +0.06 TDS to the final brew, that seems quite significant?


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## Phobic

the focus is on measuring the difference in TDS between shots/brews, we 0 the refractometer to improve measurement accuracy.

TDS for spro is somewhere like 7.4-9.5 so 0.08 isn't going to make up a massive amount, it has a bigger impact for drip, but if you always use the same water the changes in TDS will be down to the differences in the shots.

not sure you need to worry about measuring/recording the TDS of the water


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## the_partisan

I've noticed that when you press both Go and Menu together, it shows some temperature. Sometimes it is showing +0.0 and sometimes something like t=+21.7. Not sure which is displayed when, I'm assuming the latter is the room temperature?


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## ashcroc

21.7 certainly sounds like ambient temperature. Try it outside to confirm your suspicions. It'll be a lot lower this time of year if it is.


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## Scotford

Phobic said:


> not sure you need to worry about measuring/recording the TDS of the water


I always take a water tds reading when refracting so you know what pitch in what country you are playing on. Differing tds counts will give you different extraction rates.

I keep my water at the shop to around 50ppm total tds at max specifically for this reason.

Evenness evenness evenness.


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## Phobic

That makes sense in a commercial environment where you're controlling the TDS of the water you use, in a home environment when using bottled water with a consistent TDS it's a bit over kill though









not sure how controllable/consistent TDS in plumbed in filters systems are in the home though.


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## MWJB

Scotford said:


> I always take a water tds reading when refracting so you know what pitch in what country you are playing on. Differing tds counts will give you different extraction rates.
> 
> I keep my water at the shop to around 50ppm total tds at max specifically for this reason.
> 
> Evenness evenness evenness.


50ppm is 0.005%TDS to put it in perspective.

If you're brewing with 500ppm water your coffee won't taste great whatever your extraction, assuming most folk are under 200ppm the TDS of the water isn't a significant issue.

You zero with distilled/DI water because it is known datum. Your coffee refractometer isn't the right tool for assessing TDS of your brew water.


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## Scotford

MWJB said:


> 50ppm is 0.005%TDS to put it in perspective.
> 
> If you're brewing with 500ppm water your coffee won't taste great whatever your extraction, assuming most folk are under 200ppm the TDS of the water isn't a significant issue.
> 
> You zero with distilled/DI water because it is known datum. Your coffee refractometer isn't the right tool for assessing TDS of your brew water.


Not entirely the point I was making. More of reducing variables to a more manageable level.

50ppm total tds water with extract differently to one with a 125ppm tds giving two different EY% readings.


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## MWJB

Scotford said:


> Not entirely the point I was making. More of reducing variables to a more manageable level.
> 
> 50ppm total tds water with extract differently to one with a 125ppm tds giving two different EY% readings.


Sure, but the effect of brew water TDS is more of an accuracy aspect (to a point that is overkill in terms of meaningful results) more than one of consistency, with similar TDS water brew to brew, same coffee, managing your variables should be keeping you to +/-0.5%EY, or less, for 2/3 of your brews.


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## the_partisan

Does anyone have experience in mixing a reference solution? I get the slight feeling that my readings are higher than it should be - since I'm tasting the coffee is somewhat underextracted at 1.35% TDS and 20.7% EY.


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## Mrboots2u

the_partisan said:


> Does anyone have experience in mixing a reference solution? I get the slight feeling that my readings are higher than it should be - since I'm tasting the coffee is somewhat underextracted at 1.35% TDS and 20.7% EY.


Few points and questions

Are you following the vst protocol for measuring? And coffee tools

? Just coz it's 20 percent doesn't mean it will be tasty btw ...

What are you using for a reference solution .

What's your data for the brew ? Dose ? Bec weight etc ?

Lastly describe the taste as opposed to under and over extraction, how does it stack up v the tasting notes ?


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## GlennV

the_partisan said:


> Does anyone have experience in mixing a reference solution?


Yes. Add 24.9g of pure cane sugar to 975.1g of distilled water (so 1000g of soln). This should read as 2.00 tds at around 20C.


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## MWJB

the_partisan said:


> Does anyone have experience in mixing a reference solution? I get the slight feeling that my readings are higher than it should be - since I'm tasting the coffee is somewhat underextracted at 1.35% TDS and 20.7% EY.


If it is 20.7% it probably isn't under extracted with a conical burr grinder. However, if the extraction is uneven, there may be elements of under-extracted flavour at a nominal extraction. Are you stirring your pre-wet/bloom?

The coffee may play a part, if I have a natural/honey process that tastes great at 18.5% I don't beat myself up trying to nail 20%, likewise if a Kenyan tastes good around 21% I see no reason to reduce extraction, unless I get any lingering, unpleasant bitterness in the last sips.

I just brewed a cup at 20.6%EY that had under-extracted flavours too (unripe fruit, sherbet almost fizz on the tongue, background of dryness)...I suspect it was uneven.


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## the_partisan

MWJB said:


> If it is 20.7% it probably isn't under extracted with a conical burr grinder. However, if the extraction is uneven, there may be elements of under-extracted flavour at a nominal extraction. Are you stirring your pre-wet/bloom?
> 
> The coffee may play a part, if I have a natural/honey process that tastes great at 18.5% I don't beat myself up trying to nail 20%, likewise if a Kenyan tastes good around 21% I see no reason to reduce extraction, unless I get any lingering, unpleasant bitterness in the last sips.
> 
> I just brewed a cup at 20.6%EY that had under-extracted flavours too (unripe fruit, sherbet almost fizz on the tongue, background of dryness)...I suspect it was uneven.


You're probably right. Also I think my little electric grinder combined with a single pour doesn't always give the most consistent results. The drain time seems to depend on how fines are placed maybe? With same grind size I got a drain at 2:30 and one at 3:00, while the 3:00 one was perfectly sweet, the 2:30 had these underextracted notes. The 2:30 came at 20.7% and the 3:00 21.6%.


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## the_partisan

Did one more brew, though not same beans, but fairly similar. Using 1 coarser grind setting and 6 pours with 250g total and 20s between each pour, with the last pour coming at 2:10, this time it took _very_ long to drain at 4:50. The refractometer read was at 21.25% EY. Seems I would need to go coarser to hit my target of around 20%. I was quite surprised that it wasn't way overextracted since it took so long to drain. It could also be the very low mineral content water I'm experimenting with. It feels like with a fixed brew ratio, there is some limit to extraction yield.


----------



## the_partisan

For those who weight the brew water, what LRR do you get? Mine doesn't seem particularly consistent - so wondering why this is the case. For 15g/250g brews I get values that range from 2.4-2.7 and the final beverage weight can have a big impact on the final yield.

For example given: BW: 250g, Dose: 15g, TDS: 1.4

If beverage weight is 219g, this will give LRR of 2.33 and EY of 21.4%

If it was 214g, this will give LRR of 2.7 and EY of 20.9% - quite significant difference.

What causes low or high LLR? There is also quite significant evaporation happening during brewing.


----------



## MWJB

Evaporation during brewing isn't significant, it's only a couple of grams & doesn't affect the LLR or gm bev. If you've added 250g total every time, using the same method, that's consistent enough.

+/-0.25%EY isn't really what I'd call significant, less than 0.02%TDS.

Different coffees can hold different amounts of liquid at the end of brew, so can different drip brewers - flat bottomed & flat bottomed V cones hold back more than Chemex & V60. If you want to be absolutely consistent a second pair of scales on a drip stand, under the cup can see you nail gm bev to the gram every time, but personally I let all brews drip out (unless I'm being a bit nerdy) & just accept that some coffees will be different to others. For the same coffee & brewer+/-2g (1% brewed weight) might be typical without intervention, your brew water added will probably be +/-1g?


----------



## the_partisan

I saw on Scott Rao's blog that he mentioned using a settings of "0" for CO2 and H2O when calculating EY. This essentially means EY = Coffee Out * TDS / Coffee In for drip brews.

I noticed that calculating this way reduces the EY calculations compared to default settings in the VST app by 1%. I'm not sure which way is the right way to go?


----------



## MWJB

Stick to one or the other, don't mix them.

I use the VST defaults because we know roasted coffee still contains moisture & CO2.


----------



## the_partisan

Sure but it makes comparing numbers tricky. I asked him now and curious how he'll elaborate on it.


----------



## MWJB

the_partisan said:


> Sure but it makes comparing numbers tricky. I asked him now and curious how he'll elaborate on it.


Not if you're comparing numbers between your own readings via a consistent convention, or, if people state whether they have allowed for non-coffee mass.

VST developed the coffee refractometer, to me it makes sense to follow their protocol. I think at some point fairly recently the moisture aspect was inadvertently overlooked in brewing manuals (one of Scott's books clearly states "dry coffee", which could be interpreted both ways). If your dose is 3% water, you won't know whether that water was brew water, or water held in the coffee when you dehydrate samples, CBI & MIT used Schwartzmann's 1953 method for determining moisture in roasted coffee, also AOAC have an official method for measuring moisture in roasted coffee.


----------



## the_partisan

I find that following this protocol really works for me, if I want to refract:

1. Brew (drip) coffee into a glass carafe

2. Stir

3. Tare the scale with an empty mug on top. I use the therma cup, since it keeps the coffee warm pretty long.

4. Decant into the mug and note the weight.

5. Use a pipette to draw some liquid in, I do this a few times since I reuse my pipettes. Put the pipette aside. The liquid in the pipette will not evaporate.

6. Taste / enjoy the coffee for a while, and then use the pipette to drop a few drops to the metal sides, not directly on the crystal. This will rapidly cool the sample down.


----------



## Zephyp

Can you make your own distilled water with a pan on a stove and ice cubes or does it need to be prosessed in some other way?


----------



## Mrboots2u

Zephyp said:


> Can you make your own distilled water with a pan on a stove and ice cubes or does it need to be prosessed in some other way?


 A trip to B and Q is easier.


----------



## Zephyp

I'm from Norway, so I'm not so sure about that.









What am I looking for in a store? I see a lot of descriptions out there. Distilled, deionized, sterile, battery water etc.


----------



## MWJB

Distilled or deionised. Motor spares shop would have it.

Not perfumed stuff for laundry irons.


----------



## Zephyp

Do motor shops have it for filling batteries? I found "Battery Water" at Biltema, a big store that sells everything and car stuff.

The datasheet says demineralised with reverse osmosis. Maybe not the same as destilled or deionized?



> Product description:Battery water is a demineralised quality water. All impurities and minerals are eliminated. Production method: Reverse Osmosis (RO)
> 
> Applications:
> 
> Batteries, steam-irons, humidors, water based cooling systems.


----------



## MWJB

That will be fine


----------



## Zephyp

Got my VST today! The motor shop only had demineralized water (desalted, ion switched or something), so I got that. The procedure was pretty straightforward and I got a reading of 1.38%. How long should I let the brew cool before measuring? I put it in a small cup while I zeroed the refractometer and it probably sat there a couple of minutes before I put it on the reader. I should think it cools down pretty fast when first drawn into the pipette, then poured into a small cup and then put into the refrac. I also put the demineralized water into a similar cup a minute before using it to zero.

Anyone with the VST Android app here that can explain how to use it? I've tried putting in values here and there, but when I change one value it changes other values, so I'm not quite sure how to input this. Or anyone with the VST app can input it to their app (or formula) and see that I get the same EY. I haven't changed anything in the app, like Co2 and moisture.

Here's the data from the brew:

Dose: 14.45g

Brew water: 240g

Beverage: 208.8g (I weighed the server before and after brewing)

TDS: 1.38%

Brew method: V60 01. Water off boil before wetting filter. Mark's 35g regime and 6 pours. 30g bloom with a stir.

Drawdown: 3:41

Coffee: Kenyan

Taste: Not quite where I want it to be, maybe too acidic (I say that about every brew that's not ideal). I'm terrible at telling sour and bitter apart. I did not get any tingling on the tongue as I sometimes do. Not sure if that is indication of one or the other.


----------



## Mrboots2u

Zephyp said:


> Got my VST today! The motor shop only had demineralized water (desalted, ion switched or something), so I got that. The procedure was pretty straightforward and I got a reading of 1.38%. How long should I let the brew cool before measuring? I put it in a small cup while I zeroed the refractometer and it probably sat there a couple of minutes before I put it on the reader. I should think it cools down pretty fast when first drawn into the pipette, then poured into a small cup and then put into the refrac. I also put the demineralized water into a similar cup a minute before using it to zero.
> 
> Anyone with the VST Android app here that can explain how to use it? I've tried putting in values here and there, but when I change one value it changes other values, so I'm not quite sure how to input this. Or anyone with the VST app can input it to their app (or formula) and see that I get the same EY. I haven't changed anything in the app, like Co2 and moisture.
> 
> Here's the data from the brew:
> 
> Dose: 14.45g
> 
> Brew water: 240g
> 
> Beverage: 208.8g (I weighed the server before and after brewing)
> 
> TDS: 1.38%
> 
> Brew method: V60 01. Water off boil before wetting filter. Mark's 35g regime and 6 pours. 30g bloom with a stir.
> 
> Drawdown: 3:41
> 
> Coffee: Kenyan
> 
> Taste: Not quite where I want it to be, maybe too acidic (I say that about every brew that's not ideal). I'm terrible at telling sour and bitter apart. I did not get any tingling on the tongue as I sometimes do. Not sure if that is indication of one or the other.


20.81 % EY

Kenyan and acidic go hand in hand









How was it for strength ? You could go a little finer and try again.


----------



## Mrboots2u

Im on an old MacBook versions somewhere ther is probably a padlock icon that need to be unlocked for you to input .


----------



## MWJB

Put the DI water on the lens for 30s before zero'ing (press menu twice, "go" to set zero, then "go" to read the DI water - should give "0.00")

After transferring a sample to the cup to cool, leave 30s minimum.

After dropping cooled sample on the lens leave 30s minimum, then take few reads & average if they change.

I don't have any Apps but the Windows version works by setting the parameter you want to keep constant (for me that's dose to 3 digits) then you enter %TDS and use the slider/enter gm Bev & read off the %EY.

Try a little finer?


----------



## Zephyp

Mrboots2u said:


> 20.81 % EY
> 
> Kenyan and acidic go hand in hand
> 
> 
> 
> 
> 
> 
> 
> 
> 
> How was it for strength ? You could go a little finer and try again.


I definitely want the acidity, but it wasn't quite balanced. I think strength was fine, I've been using 1:16.6 for a long time.



Mrboots2u said:


> Im on an old MacBook versions somewhere ther is probably a padlock icon that need to be unlocked for you to input .


Ah, yes, the padlock gave me more control. It does still change BW or BEV whenever I change the other. Should I just input BEV and leave BW be? Some water will of course evaporate during the brew, maybe that's where the difference is. If I try to input 240 BW, BEV automatically goes to 214 and when I input 209 BEV, BW automatically goes to 235.

When I put in 14.45, 208.8 and 1.38, I get 20.77 EY.



MWJB said:


> Put the DI water on the lens for 30s before zero'ing (press menu twice, "go" to set zero, then "go" to read the DI water - should give "0.00")
> 
> After transferring a sample to the cup to cool, leave 30s minimum.
> 
> After dropping cooled sample on the lens leave 30s minimum, then take few reads & average if they change.
> 
> I don't have any Apps but the Windows version works by setting the parameter you want to keep constant (for me that's dose to 3 digits) then you enter %TDS and use the slider/enter gm Bev & read off the %EY.
> 
> Try a little finer?


I didn't try to read the DI water, but I'll do that next time.

When you say take a few reads, you mean just leaving the sample on the prism and read it a few times in succession?

Yeah, I'll try a bit finer and see what happens.


----------



## MWJB

Zephyp said:


> When I put in 14.45, 208.8 and 1.38, I get 20.77 EY.
> 
> When you say take a few reads, you mean just leaving the sample on the prism and read it a few times in succession?
> 
> Yeah, I'll try a bit finer and see what happens.


Sure, leave the same sample on the lens and press "go" 3 or 4 times.

20.77% & 20.81% are in effect the same reading. 0.04%EY isn't enough to indicate a difference.


----------



## Zephyp

1.41, 1.40, 1.40 and 1.40% on the next brew. The BEV however, I measured to 207 (down from 208.8), which lowered the calculated EY, ending up at 20.89%. Just slightly higher. Drawdown was just 7 seconds longer, so I didn't expect a huge change.

Well, I'm started and I'll record the brews in a log to see how it changes as I change the grind and pour regime. The DI test read 0.00. I've been using the same pipettes and clean them with DI water after use. It might still have some particles in there, but when you draw in and pour out the sample multiple times before taking the final sample, I have trouble imagining it making a big enough difference on the test. I don't mix the pipette for DI and brew though.

I see that Mark's getting good brews in a range from 18.5-22%, which is understandable since every bean is different. When I'm testing and tasting, what outer limits should I stay within? If I now wanted to increase the EY and see how it changed the brew, do I stop at 22% before I try going the other way, towards 20 and below? Of course, if the brew taste great at 22%, there's no need, but if I'm not happy, I assume I want to go the other way next time.

Anything else to keep in mind while experimenting on this?


----------



## Mrboots2u

Zephyp said:


> 1.41, 1.40, 1.40 and 1.40% on the next brew. The BEV however, I measured to 207 (down from 208.8), which lowered the calculated EY, ending up at 20.89%. Just slightly higher. Drawdown was just 7 seconds longer, so I didn't expect a huge change.
> 
> Well, I'm started and I'll record the brews in a log to see how it changes as I change the grind and pour regime. The DI test read 0.00. I've been using the same pipettes and clean them with DI water after use. It might still have some particles in there, but when you draw in and pour out the sample multiple times before taking the final sample, I have trouble imagining it making a big enough difference on the test. I don't mix the pipette for DI and brew though.
> 
> I see that Mark's getting good brews in a range from 18.5-22%, which is understandable since every bean is different. When I'm testing and tasting, what outer limits should I stay within? If I now wanted to increase the EY and see how it changed the brew, do I stop at 22% before I try going the other way, towards 20 and below? Of course, if the brew taste great at 22%, there's no need, but if I'm not happy, I assume I want to go the other way next time.


Firstly , how did those brews taste? to some degree the amount you can push EY will be down to the grinder and water as to if they are tasty and in the end only you an evaluate that. I enjoyed v60 brews 21% ey ish with the EK , bean dependent tbh.

In the end though its just a measure. My 21% brew with a hand grinder will be different to a 21% brew with a bulk grinder ( even if the pour and dose and bed weight and tds are the same ) . Try going finer again and taste .


----------



## MWJB

Zephyp said:


> I see that Mark's getting good brews in a range from 18.5-22%, which is understandable since every bean is different. When I'm testing and tasting, what outer limits should I stay within? If I now wanted to increase the EY and see how it changed the brew, do I stop at 22% before I try going the other way, towards 20 and below? Of course, if the brew taste great at 22%, there's no need, but if I'm not happy, I assume I want to go the other way next time.
> 
> Anything else to keep in mind while experimenting on this?


20.77 to 20.89 is close enough to still regard as 'no change'.

For Kenyans I wouldn't aim to stay below a limiting number, they're usually very soluble and can be way over 20% at an under developed roast. I'd use Kenyans to establish the higher tolerance of your range, I find they taste good (to me) often 21%+, maybe even a tad over 22%.

I wouldn't try and establish a datum for Kenyans around what I would consider an average extraction for a range of coffees (for me, an average will be a little over 20% for at least 10 different coffees).

If you go


----------



## Zephyp

Mrboots2u said:


> Firstly , how did those brews taste? to some degree the amount you can push EY will be down to the grinder and water as to if they are tasty and in the end only you an evaluate that. I enjoyed v60 brews 21% ey ish with the EK , bean dependent tbh.
> 
> In the end though its just a measure. My 21% brew with a hand grinder will be different to a 21% brew with a bulk grinder ( even if the pour and dose and bed weight and tds are the same ) . Try going finer again and taste .


The primary reason for getting the VST was because I find it really difficult to tell where to go based on taste. I know what good coffee taste like, but I'm not very good at putting the taste when I don't like it into words. The brews weren't terrible, but they weren't ideal. I want to say it was too acidic, but I've had brews where I thought it was too acidic and my girlfriend said it was too bitter. Who's "correct" I can't say, but generally she's got a better palate than me when it comes to coffee, wine and food. Maybe using the refractometer and tasting the difference of 18, 20 and 22% EY will improve my palate a bit.









I know it's just numbers, but I think it will make it easier to figure out where I'm at and where I want to go. I don't expect I could even use the EY from the roaster or coffee shop since they might have different wanter and a better grinder. My Comandante doesn't match the EK43.

I'll go even finer next time and see if I get readings closer to 22% and how that taste. I often see people talk about an 18-22% range, which I think is the SCAA recommended range too. Before tasting and testing, I can't know at which EY I will enjoy the coffee the most, so I'll just have to test, taste and record.

I normally just make one brew a day, but I see that I can easily end up making a lot more coffee with this gadget. At least initially when I'm figuring things out and dialling in brews.


----------



## Zephyp

MWJB said:


> 20.77 to 20.89 is close enough to still regard as 'no change'.
> 
> For Kenyans I wouldn't aim to stay below a limiting number, they're usually very soluble and can be way over 20% at an under developed roast. I'd use Kenyans to establish the higher tolerance of your range, I find they taste good (to me) often 21%+, maybe even a tad over 22%.
> 
> I wouldn't try and establish a datum for Kenyans around what I would consider an average extraction for a range of coffees (for me, an average will be a little over 20% for at least 10 different coffees).
> 
> If you go
> 
> If you go from a Kenyan til a Braizilian, do you just use your brew experience to change your pour regime?
> 
> Ideally, I want to find a grind where I can just change the pour regime to manipulate EY across the range of coffee I buy. I'm usually drinking Africans, mostly because I often find the South-Americans to taste too much like "regular coffee" and not finding the notes on those. I hope I'll be better able to find them when working with the VST. I've had some amazing Brazilians, but usually when I buy something from there, I'm not too happy with it. Based on my experience, I've imagined it being because those notes don't stand out as much as Africans, and are tougher to find if the brew isn't balanced.
> 
> Just changing grind is fine for now. It's an easy way to change EY and taste. Once I've gotten some work in, I can try to settle on a grind and work on pour regime.


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## MWJB

Zephyp said:


> If you go from a Kenyan til a Braizilian, do you just use your brew experience to change your pour regime?
> 
> Just changing grind is fine for now. It's an easy way to change EY and taste. Once I've gotten some work in, I can try to settle on a grind and work on pour regime.


I generally don't change anything once grinder & brewer are dialled in for similar roast levels (when I say similar, I mean filter roasts from speciality roasters, if I were to brew some supermarket beans I'd need to change).

I can if I want to, of course, and there can be more wrong with a roast than the EY you are getting, but having some coffees fall 18-20% and others fall 20-22% (>95% falling 18-22% overall) seems to work out pretty well for me. I expect them to be different & enjoy the difference, I don't try and brew them differently to make them all extract the same, that sounds like a chore & a hiding to nothing 

At some point the experimenting has to give way to relaxing & enjoying the scenery.


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## Zephyp

MWJB said:


> I generally don't change anything once grinder & brewer are dialled in for similar roast levels (when I say similar, I mean filter roasts from speciality roasters, if I were to brew some supermarket beans I'd need to change).
> 
> I can if I want to, of course, and there can be more wrong with a roast than the EY you are getting, but having some coffees fall 18-20% and others fall 20-22% (>95% falling 18-22% overall) seems to work out pretty well for me. I expect them to be different & enjoy the difference, I don't try and brew them differently to make them all extract the same, that sounds like a chore & a hiding to nothing
> 
> At some point the experimenting has to give way to relaxing & enjoying the scenery.


The less I have to adjust, the better. It wouldn't be to make everything taste the same, but rather bring out the flavors of the individual beans. A balanced brew where the one from Honduras taste like chocolate and the African like citrus. I don't think I could ever make one taste like the other and still be good tasting.


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## Zephyp

Today I made a brew which gave readings of: 1.36, 1.37, 1.38, 1.39, 1.40, 1.41, 1.41, 1.41. Could the change from first to last reading be change in the temperature of the sample? I gave it at least 1 minute in a cup and another minute on the VST before running it, but coming straight from the server it was perhaps it was still too hot.

I tightened the grind on the Comandante with 3 clicks, drawdown was 3:50. Assuming I performed the test correctly, could a lack of measurable and tastewise difference be attributed to technique? I was expecting a bigger difference in taste and TDS with 3 clicks finer. I though the brew had some difference to yesterday, but not significantly.

My experimentation with brewing using an AP or something similar to distribute the water over the V60 and not disturb the bed as much was encouraged by a search for better consistency. I've seen it before too, that I can end up with pretty different drawdown times and taste in the cup using the same recipe. Maybe I'm not careful enough with my technique.

Of course, one sample is far from enough to make conclusions, but every brew is a bit of experience. I might intentionally want to brew to the limits of EY just to see how it taste and if my palate can make sense of it. I find it easier finding a middle spot if I know the outliers.

I will find some articles and read up on grind size, its relation to TDS and taste. I got some holes in my understanding of coffee brewing and it would be interesting to fill some of them. I've got some material on this forum, the Barista Hustle articles and some other stuff.

I've so far been doing the testing right after brewing and since it doesn't take more than a few minutes, I still got a hot brew to enjoy. If I at some point wanted to delay the testing several hours, would the sample still be useable? Maybe I'd need a small container I can put a lid on to prevent water from evaporating? If I made two brews one day and put the first sample in a container, let it sit in a cupboard 4-5 hours, made the second brew later, also putting it in a container, then testing both samples after I was done drinking the second brew, would those tests be reliable? Maybe shake the container a bit first to swirl around any particles that might have settled on the bottom.


----------



## MWJB

I've never seen that large a swing in readings, so yes, I suspect temp may have been too high on the 1st readings.

You gave us the TDS but not the EY?

I don't know how much change 3 clicks makes on a Commendante, how many to a full turn.

I still find results for V60 better with a kettle, good with a AP but more faff. For the Kalita Wave I think the AP screen works better with the shallower flat bed.

For the same coffee, same weights, same grind, I'd expect you to be able to keep 10 brews within a %, or a std dev in EY of less than 0.5%EY.

So, making maybe very small changes in grind & natural deviation in EY is giving too high a noise floor for you to see a significant difference?

Push the issue, try a quarter turn on the grinder?


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## MWJB

Samples will suffer from evaporation, sample straight after brewing & record results. You want to correlate that reading with a change in taste for the coffee/change in method you just made, whilst drinking the coffee at normal temp, so doing it live would be an advantage?


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## Zephyp

Oh, yeah. I'm using the same recipe, so EY will be pretty much the same. Small changes in beverage weight can affect the result. With 1.41 and 209 BEV, I get 21.24%. I'll try even finer and see what happens. The recommended range for V60 with Comandante is 20-25 iirc, and I'm now at 20 or something.

Maybe I'll try AP on Kalita then. I got lots of filters, but it doesn't get much use nowadays.

Good point on comparing taste and EY at the same time. Could of course note taste while drinking and compare later. Maybe I'll try one day to test before drinking and leave a sample in a closed container for testing later, to see if I get the same result.


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## MWJB

Zephyp said:


> Oh, yeah. I'm using the same recipe, so EY will be pretty much the same. Small changes in beverage weight can affect the result. With 1.41 and 209 BEV, I get 21.24%.


Even using the same recipe & grind, for a 200g average brew, you'll see maybe a 5g span of brewed weights. That's about 0.5%EY's worth at typical drip ratio. Weigh each brew.

Maybe someone can pour to the gram each time on brew water, I can't. Beverage mass (for drip) will vary slightly more than water input. Basically, when repeating brews you're going to get some variance and smallest to largest it looks like this:

Dose - no reason why this shouldn't be the same to 0.1g

Brew water stdev of ~1g for a 230g pour

Bev mass stdev of ~2-3g for 200g in cup

EY is the next smallest variance (no change in grind)

Brew water absorbed

Brew time

Draw down time after the last pour interval ends is the largest variance.


----------



## Zephyp

I noticed that even the infusion of the paper made a difference since I weighed the server after doing so, and the few drops that remained in the server added a gram or two. Last brew today I infused it over a cup and not the server I brewed in. Then I can use the same server weight each time and just subtract from BEV+server.

Last brew of the day: 4 clicks finer and I knew this one would make a difference. 208 BEV, 4:34 drawdown (at 4:10 it seemed to nearly come to a complete stop having a little water left). With this fine grind, I had to really stir the bloom. I saw when stirring that a few groups of dry grounds popped up. 1.47x4 TDS and 22.07 EY. I thought it had more fruitiness and distinction, but also introduced more bitterness and drying mouthfeel. I suspect the bitterness will increase if I push it further, and the brewing might come to almost a complete stop during drawdown.

In your experience, is there an EY range where certain origins taste better? I often see people going finer on Africans, which I suppose increases EY. In your log you seem to hit averages from 19 to 21 across different origins and methods. I started out at 20.7 and now tried 22. Something between there is probably ok, but I'd like to see what below 20 taste like.


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## MWJB

Zephyp said:


> I noticed that even the infusion of the paper made a difference since I weighed the server after doing so, and the few drops that remained in the server added a gram or two. Last brew today I infused it over a cup and not the server I brewed in. Then I can use the same server weight each time and just subtract from BEV+server.
> 
> Last brew of the day: 4 clicks finer and I knew this one would make a difference. 208 BEV, 4:34 drawdown (at 4:10 it seemed to nearly come to a complete stop having a little water left). With this fine grind, I had to really stir the bloom. I saw when stirring that a few groups of dry grounds popped up. 1.47x4 TDS and 22.07 EY. I thought it had more fruitiness and distinction, but also introduced more bitterness and drying mouthfeel. I suspect the bitterness will increase if I push it further, and the brewing might come to almost a complete stop during drawdown.
> 
> In your experience, is there an EY range where certain origins taste better? I often see people going finer on Africans, which I suppose increases EY. In your log you seem to hit averages from 19 to 21 across different origins and methods.


OK so it looks like you have found a limit, back off a tad to drop EY & make wetting at the bloom easier.

'Africans' covers the whole gamut really. Kenyans & Rwandans may end up in the higher end, Ethiopians can fall anywhere. I don't change grind setting based on origin, only when dialling in a new grinder/brewer, or if my average EY is so high/low to have anumber of brews over/under extract. I change grind setting very infrequently, months between changes rather than days.


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## Zephyp

Should I adjust LRR to the ratio I usually get between BW nand BEV? Does it matter much what LRR is at if I don't change it? Default was 2.1, which gave BW of 235, when I pour 240. If I adjust LRR to 2.55, BEV and BW matches my brews. Changing it doesn't produce a significant change in EY, so I assume it doesn't matter much.


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## MWJB

Zephyp said:


> Should I adjust LRR to the ratio I usually get between BW nand BEV? Does it matter much what LRR is at if I don't change it? Default was 2.1, which gave BW of 235, when I pour 240. If I adjust LRR to 2.55, BEV and BW matches my brews. Changing it doesn't produce a significant change in EY, so I assume it doesn't matter much.


If you have scales handy, weigh the brew & subtract server, don't use the LRR presets.

LRR is something I would use if I was looking for ball-park, or if weighing the beverage was impractical every brew (then I'd measure 10 brews & use the average). You might even find that changing the grinder changes LRR, as does changing grind setting/brew weights for the same brewer.

The important things you need to calculate the drip EY are dose, BEV & %TDS. I weigh each brew (to the g) & ignore BW & LRR, inputting BEV & %TDS.


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## Zephyp

Maybe I should probe the sample with a thermometer before testing. Yesterday I went 10 clicks coarser and today 4 more. First test today read 1.27, but the next was 1.31. The following tests climbed up to 1.34. Then I removed the sample, wiped the prism and added a second sample from the same cup I used to bring it down in temperature. That sample read 1.38.

Could you even be waiting too long, so that parts of the sample evaporate and the TDS effectively increase? Maybe I should draw a larger initial sample into the cup for cooldown.

Drawdown was 3:54, which was considerably longer than yesterday's 3:36, with today's grind being coarser. I wonder if the way I stir the bloom and amount of shake after the last pour cause these differences. I see what you mean by the drawdown having the largest variance.

Does the amount of sample I put on prism matter? Could different amounts provide different results?


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## MWJB

Zephyp said:


> Maybe I should probe the sample with a thermometer before testing. Yesterday I went 10 clicks coarser and today 4 more. First test today read 1.27, but the next was 1.31. The following tests climbed up to 1.34. Then I removed the sample, wiped the prism and added a second sample from the same cup I used to bring it down in temperature. That sample read 1.38.
> 
> Could you even be waiting too long, so that parts of the sample evaporate and the TDS effectively increase? Maybe I should draw a larger initial sample into the cup for cooldown.
> 
> Drawdown was 3:54, which was considerably longer than yesterday's 3:36, with today's grind being coarser. I wonder if the way I stir the bloom and amount of shake after the last pour cause these differences. I see what you mean by the drawdown having the largest variance.
> 
> Does the amount of sample I put on prism matter? Could different amounts provide different results?


No idea why you are seeing such swings in the readings. I trust you are stirring the cup well before taking a sample for cooling?

0.3ml (0.2 to 0.4ml) is the ideal sample on the prism, but try and keep these the same for each sample. Look at the width of the band of coffee around the prism, on the steel dish.


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## Zephyp

Poorly executed I think. The next brew was more consistent, giving readings of 1.29, 1.29, 1.30, 1.29. I poured a bit larger amount into a bit larger cup, swirled it more and waited a bit longer. In the cup it was 33C, and after pipetting and dropping on the prism and waiting more, it probably got closer to equilibrium.

210 BEV, 14.45 dose, 1.29 TDS = 19.53 EY.

I thought the cup had less of the unpleasant characteristics, which brought forth more clarity, but was also a bit weaker. The grind is quite coarse, 34 on the Comandante, but still taking 3:35 to draw down. I guess it's the nature of some Africans to brew slower. It would've been interesting to have a different bean to brew every other cup with and see how it turned out. Something from South America. I'll buy two bags of different origin sometime and compare them as I go.

So far, I think the refractometer is an interesting gadget. Seeing the TDS compared to brew time and grind demonstrates that it can be difficult to compare two brews where you see differences, but don't taste too much of it. As you said, variance can be pretty high. I made two brews, one with setting 27 and one with 34, which had the same drawdown time, one with 20.6 EY and one with 19.6. Previously, I would've expected the difference in grind to show more on the brew time, but I see now that I shouldn't pay it too much attention.


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## Nod

Hi just got our new refractometer - exciting! I wonder if anyone has tried the Chinese VST equivalent filters? Can you use these cheap alternative to the VST originals? Thanks


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## berthadee

nice info...


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## Zephyp

A quick question about calculating EY for pour over.

I put the following data into the VST app:

Dose: 14.4g

BEV: 211g

TDS: 1.44

EY: 21.98%

How does it calculate that value and is it something I can put into my Google sheet? I tried BEV*TDS/Dose, but that gives 21.1 Is there some kind of factor in there that I'm missing? Since I only input those three variables, I was thinking the missing number might be a constant, or does it change depeding on the data I put in? It's not a big problem, but if I can avoid having to use the app to calculate EY every time, that would be nice.


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## MWJB

Zephyp said:


> A quick question about calculating EY for pour over.
> 
> I put the following data into the VST app:
> 
> Dose: 14.4g
> 
> BEV: 211g
> 
> TDS: 1.44
> 
> EY: 21.98%
> 
> How does it calculate that value and is it something I can put into my Google sheet? I tried BEV*TDS/Dose, but that gives 21.1 Is there some kind of factor in there that I'm missing? Since I only input those three variables, I was thinking the missing number might be a constant, or does it change depeding on the data I put in? It's not a big problem, but if I can avoid having to use the app to calculate EY every time, that would be nice.


Just use the Bev*TDS/dose 21.1% calculation for your google sheet, if the figures are all the same convention then you are just looking at relative extractions.


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## the_partisan

Zephyp said:


> A quick question about calculating EY for pour over.
> 
> I put the following data into the VST app:
> 
> Dose: 14.4g
> 
> BEV: 211g
> 
> TDS: 1.44
> 
> EY: 21.98%
> 
> How does it calculate that value and is it something I can put into my Google sheet? I tried BEV*TDS/Dose, but that gives 21.1 Is there some kind of factor in there that I'm missing? Since I only input those three variables, I was thinking the missing number might be a constant, or does it change depeding on the data I put in? It's not a big problem, but if I can avoid having to use the app to calculate EY every time, that would be nice.


It's because of CO2 and Moist variables, they're non-zero by default in the VST App.

The full formula is:

=BEV*TDS/DOSE/(1-%H2O-%CO2)


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## Zephyp

Thanks both of you. Since I will use it primarily for myself I'll just keep it at 0 and 0.

Been trying a few things and starting to see how big change the pour regime can create. Made a few cups the last days that I wasn't quite happy with, but today, when I of course didn't measure anything it was very good. Made a small adjustment on the grinder which I think is still within the 10-13%


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## madrian

Sorry for replying to this old topic, but this seem to be best place to ask about this refractometer. It's a 100$ refractometer from China. Anyone using it? How does this compare to the well known VST and others? I need it only for home use.


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## MWJB

madrian said:


> Sorry for replying to this old topic, but this seem to be best place to ask about this refractometer. It's a 100$ refractometer from China. Anyone using it? How does this compare to the well known VST and others? I need it only for home use.


 I have one, and an Atago and a VST.

The VST is really the only one with enough precision to meaningful with brewed coffee.

All 3 need syringe filtering for espresso/coffee with suspended solids.

If you want to go ahead with the Amtast for espresso, fine but just don't get too worked up if your shots seem less consistent than you are expecting. I found the Amtast sometimes read half a % low, then half a % high, then the same as the VST. Say you get a reading of 15/16%EY then you may want to act if a malfunction is confirmed by taste, but if your taste is good and it gives a reading of half a %EY to a whole %EY outside of what you expect, I wouldn't fret, not take it too literally and think you are hitting some hitherto unknown region of interest.

An aspect not often mentioned is that it's a lot quicker to take readings with the VST, but whether that is enough incentive for you to spend so much more is up to you.

With any EY readings, once you have got past any severe malfunctions in brewing, then keeping an eye on your consistency (correlated to taste scoring) is probably the most useful use of it, look at averages built up over time and standard deviations. Compare like with like (same brew ratio, same method re brewer, espresso, drip, immersion etc.)


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## madrian

@MWJB awesome, thanks for this write up.


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## madrian

@MWJBone more question: I calibrated using distilled water, reading 0.00. Then I measured regular tap water and also got reading 0.00 - is this malfunction? For coffee -espresso- I got pretty good reading, around 21%.

Is there any solution against which I can test? I mean XY gramm of sugar to XY gramm water should be read XY value.


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## MWJB

madrian said:


> @MWJBone more question: I calibrated using distilled water, reading 0.00. Then I measured regular tap water and also got reading 0.00 - is this malfunction? For coffee -espresso- I got pretty good reading, around 21%.
> 
> Is there any solution against which I can test? I mean XY gramm of sugar to XY gramm water should be read XY value.


 EY varies with origin, amongst other things. Ethiopians, Kenyans, Colombians might be fine at 21%, Brazil, Guatamala, Costa Rica might be lower and still taste good. A ~4% span, averaging accross all origins, is normal.

What TDS is your tap water (the one thing about tap water, is that there's no such thing as "regular")? If you live in a soft water area, I guess this could be possible.

We use distilled water to calibrate because the refractive index of distilled water is a known. I just calibrated the VST & Amtast with distilled & read tap water (312) on a conductive TDS meter and it read 0.04 on the VST.

It read 0.07-9 on the Amtast in native mode, 0.07 in TDS mode.

None of this means very much. Tap water is way out of the typical range that espresso, or even filter coffee inhabits.


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## madrian

"We use distilled water to calibrate because the refractive index of distilled water is a known. I just calibrated the VST & Amtast with distilled & read tap water (312) on a conductive TDS meter and it read 0.04 on the VST.

It read 0.07-9 on the Amtast in native mode, 0.07 in TDS mode. "

I feel so dumb. In Amazon's description is 0.00 resolution for this cheap meter, but in real life the resolution is 0.0. This is why I am getting 0.0 for distilled & tap water (if difference is in the 0.00 range).

Now I am thinking if I should return it or keep it.


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## MWJB

madrian said:


> "We use distilled water to calibrate because the refractive index of distilled water is a known. I just calibrated the VST & Amtast with distilled & read tap water (312) on a conductive TDS meter and it read 0.04 on the VST.
> 
> It read 0.07-9 on the Amtast in native mode, 0.07 in TDS mode. "
> 
> I feel so dumb. In Amazon's description is 0.00 resolution for this cheap meter, but in real life the resolution is 0.0. This is why I am getting 0.0 for distilled & tap water (if difference is in the 0.00 range).
> 
> Now I am thinking if I should return it or keep it.


 If you like short shots of espresso, like 1:2. then the error margin in EY decreases.

Even if you get the Amtast with a 2nd decimal place, you're going to get a big spread with brewed coffee.


----------



## Zephyp

What is the simplest way to accurately measure TDS for filter coffee with a refractometer? When I first bought mine I followed some website I found, which used alcohol wipes and pipettes.

Today I tried simplifying it, but I don't know if that affects the accuracy or chances of inaccurate measurements.

The VST was clean and I added DI water with a clean metal spoon to zero it (how often is this necessary?). Then I soaked up the DI water with paper towels before wiping the sensor area with a lint free cloth (wine glass dish towel). Next came the coffee, added with another clean spoon, allowed to cool for a minute before taking the measurements. After that I soaked up the coffee with paper towels, added som DI water to do circular sweeps with another piece of paper towel before ending with circular sweeps with the wine towel.

Can this method lead to bad readings? Anyone got a better way to do it, preferably without more tools than necessary and ideally something I already got in the kitchen? I'd prefer not using pipettes or alcohol wipes, but I also want good measurements, so I don't want to make them a lottery just to make the process simpler.


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## MWJB

Zephyp said:


> Can this method lead to bad readings? Anyone got a better way to do it, preferably without more tools than necessary and ideally something I already got in the kitchen? I'd prefer not using pipettes or alcohol wipes, but I also want good measurements, so I don't want to make them a lottery just to make the process simpler.


 As long as you are consistent with the amount of coffee placed in the VST, I don't see an issue. 0.3ml gives me about a 2mm halo around the sensor.

You will probably need to use alcohol, at least occasionally if you have trouble setting zero. You don't necessarily need alcohol wipes, you can buy a bottle of isopropyl alcohol & use lint free cloth/paper wipes.

I don't mind using pipettes, I have a few in rotation at any one time, flush them & then dry them.

Are you getting wildly irregular readings?


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## Zephyp

MWJB said:


> As long as you are consistent with the amount of coffee placed in the VST, I don't see an issue. 0.3ml gives me about a 2mm halo around the sensor.
> 
> You will probably need to use alcohol, at least occasionally if you have trouble setting zero. You don't necessarily need alcohol wipes, you can buy a bottle of isopropyl alcohol & use lint free cloth/paper wipes.
> 
> I don't mind using pipettes, I have a few in rotation at any one time, flush them & then dry them.
> 
> Are you getting wildly irregular readings?


 I have wondered if the amount matters. I haven't measured it, but try to use about the same amount. Easier with a pipette than spoon perhaps. I'll keep that in mind.

I got a bottle with isopropyl.

Not yet, I just started doing readings like this. Just wanted to check before doing a bunch of them. I suppose I'll see when I keep measuring similar brews how consistent it is. Thanks.


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