# How a coffee refractometer helps make your coffee better



## MikeHag (Mar 13, 2011)

*Question: *How do you know whether your coffee is too strong... too weak... whether you have eeked out too much from the grinds than you should have (over-extracted)... or perhaps not washed enough of the coffee particles off the grinds and into your cup (under-extracted)?

Tasting it is one way... but everyone's taste buds are different.

There are actually established standards to help you brew the 'ideal' coffee, based upon years of research and recording the taste preferences of many people. You can use a device called refractometer to measure your coffee and compare it with these standards.

This is where coffee gets geeky - too geeky for some, but since this forum has its fair share of technically minded people on here then some of you may love the thought of being able to control coffee rather than letting it control you.

Here is an abstract from the patent application for the VST Refractometer.

"A coffee refractometer includes a prism that receives a brewed coffee sample, thus forming a prism-sample interface. A processor or microcontroller controls a light source to provide incident light to the prism-sample interface. The prism-sample interface refracts light toward a photodetector. A temperature sensor provides temperature information to the processor. The refractometer includes a memory store that stores a TDS formula that expresses the TDS of brewed coffee as a function of the index of refraction (n.sub.s) of brewed coffee and the temperature of brewed coffee. The processor determines the TDS of the brewed coffee sample by accessing the TDS formula in the memory store and employing the determined index of refraction (n.sub.s) of the brewed coffee sample to find the TDS from the TDS formula. The refractometer displays the resultant TDS % on a display of the refractometer and/or transmits such information to an information handling system."

TDS stands for Total Dissolved Solids. It is a measure of the amount of coffee that has ended up in your cup... aka the strength of your coffee. It is the gateway to answering the question posed at the start of this post. The refractometer gives you brewing control.

Like most things geeky and technical, once you learn how controlled brewing works it is actually easy... no more difficult than learning to set the timer on Sky Plus! We pay a lot of money for great coffee beans, so it makes sense to brew them correctly.


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## Ian_G (Nov 10, 2011)

It sounds like a great idea, but how much does a refractometer cost? And are they easy to come by?


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## MikeHag (Mar 13, 2011)

Glad to hear that it's of interest









I think the price of a refractometer probably reflects the type of person who is likely to buy one. It perhaps ISN'T for those who are looking for low cost coffee, and probably IS for those who are likely to spend a few hundred pounds on, say, a good espresso grinder. For anyone who isn't into espresso and therefore hasn't had to invest in a machine and a grinder, and prefers brewed coffee from the likes of Has Bean & Square Mile etc, I'd say this is one thing you should definitely consider saving up for. The device that seems best comes in at around £250 (for their entry level model) from VSTApps (the same guys who do the VST basket).

However, there are alternative and cheaper ways to start brewing in a controlled way. I don't have a refractometer yet (I'm about to buy one), but I've been using a TDS Meter which fulfills a similar function but in a less accurate way, and for a lot less money... I paid around £40.

I think the key thing I'd like to advocate is not necessarily the refractometer itself, but rather the use of controlled brewing... measuring your brews in order to help improve them. Progressing to using a refractometer is a thing to aim for, in my view, but not having one doesn't prevent us from improving our brews by understanding how brewing controls work. I'd love to see more discussion on here about how to achieve a particular extraction or TDS, or whether a particular coffee is better at 55g per Litre, 60g per Litre or 65g per Litre.


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## vintagecigarman (Aug 10, 2009)

I know that Glenn has had a refractometer and extractmojo for some time now - be very interested to hear from him how useful it has been.

I researched them some time but ruled it out as a bit too expensive (and too Heston Blumenthal) for the likes of me!


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## MikeHag (Mar 13, 2011)

I really think every good coffeeshop needs one, particularly if they are serving brewed coffee, and if that's the case then it would be natural for home baristas to end up using them since we like to make coffee at home as good if not better than the coffeeshops do. I just hope that the price falls soon. After recording my extractions using the TDS Meter I've realised how seldom I am able to brew coffee with a consistent flavour/extraction profile, and how invaluable a refractometer would be.


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## CoffeeMagic (Aug 7, 2011)

...so how do you set the timer on SkyPlus? I don't know, so wouldn't be of much use to me









I could see where this would be very useful in a cafe, but are we that fussy as to require that level of precision at home? I like to think everything has a tolerance - even a cup of coffee.


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## vintagecigarman (Aug 10, 2009)

I can understand their value in a commercial environment, where the cost, being set off against tax, is comparatively immaterial. Are they as much use for espresso as for brewed coffee?


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## MikeHag (Mar 13, 2011)

Yes, the model shown is able to do both.

I definitely expect many people to say it's a step too far... but to be honest I think it's no further than many of the lengths home baristas are going to these days. There are some surprising amounts being spent on espresso machines and grinders, and this device is cheaper than those. But like I say, not for everyone but I certainly think it should be. I do find it curious that we go to such lengths to buy top quality beans and try to identify varietal distinctions and aromas mentioned in cupping notes, when in reality a large proportion of people aren't going to find all those characteristics because they haven't brewed it to its full potential. As the man said... "Your coffee may well taste great. In fact it probably does taste great, as the raw materials are exceptional. That doesn't mean that it couldn't taste better. Being satisfied is a terrible place to be. "


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## CoffeeMagic (Aug 7, 2011)

I suppose it comes down to need factor also. If only a roast colour analyser was £250 I'd snatch it from their hands









I certainly wouldn't dispute the influence it would have on the consistency of achieving the perfect brew each time, but I also enjoy the 'adventure' of being not-so-perfect


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## garydyke1 (Mar 9, 2011)

Group buy anyone??









I really want one but cant justify the 250 quid ...yet. Some days my coffee isnt as good as I know it could be, when this starts to really annoy me ..ill take the plunge


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## sicknote (Sep 5, 2011)

I'm wondering how many people were involved in developing the standards for the 'ideal coffee'. It's certainly an interesting subject, but do you brew your coffee to the standards or do you brew for personal preference?

Some of the best brewed coffee I have tasted was in Ethiopia. The beans are roasted over a flame, ground using a wooden mortar and pestle, poured into a clay jebena and left to brew. I wonder what they would think of a refractometer?


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## vintagecigarman (Aug 10, 2009)

At the end of the day, I make coffee for myself, my wife and a few friends and visitors. I can't see that ever changing, nor would I want it to. There is only one opinion that counts about the quality of my coffee - mine.

I roast 8oz of coffee at a time, and generally have the variables adjusted to my satisfaction within 2 or 3 pulls on a new roast. After that it only needs minor tweaks between shots. It would be great to have a magic meter that pointed me in the right direction and told me that my results were up to standard, but I'm currently more than happy with my empirical trial and error method.

At the end of the day, taste is a totally subjective matter - we all know that some beans that blow some users socks off are detested by other, equally discerning, consumers. Doesn't matter how well the brew meets any given standard, it's the taste that counts.

I totally understand their value in a commercial setting - but it's one step too far for me - a bit like examining the output of my amplifier through an oscilloscope instead of speakers.

Sent via Tapatalk


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## MonkeyHarris (Dec 3, 2010)

Found myself looking at these a while back. It was at this point I realised I had a problem. For now it's been put in the "If I win the lottery" basket or my wife leaves me.


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## MikeHag (Mar 13, 2011)

sicknote said:


> I'm wondering how many people were involved in developing the standards for the 'ideal coffee'. It's certainly an interesting subject, but do you brew your coffee to the standards or do you brew for personal preference?


Yeah, that's the right question isn't it. I think the answer (at least for a home barista) has to be to brew to your own personal taste preference. But the questions then become:

- how do you know what that preference is? How can you express it? Saying "I like a strong coffee" doesn't mean much.

- how to do brew so that you achieve that preference more often, rather than sometimes getting a good cup and sometimes not?

- when you have made a cup and it doesn't taste as good as the last one you made, what should you do next time to improve it? We already know from espresso that randomly increasing or decreasing dose doesn't help. *What direction should you go in?*

I think that anyone interested in these questions would love the results gained from controlled brewing. (It's all in Scott Rao's book, by the way.) And a refractometer is SatNav for coffee. It tells you exactly where you are... i.e. the brew stats for the coffee you've made. Using that info, and the understanding of brewing techniques that you probably already have, you can then move in the correct direction and hear those magic words "you have reached your destination", rather than ending up in Milton Keynes.

I don't think anyone is saying that coffee must fall into specific parameters to be classed as good... I don't believe it would be supported by the coffee industry if it was that prescriptive... but it does promote a higher standard of coffee brewing, and is part of the SCAE's Gold Cup and BrewMaster initiative, so I just think, why shouldn't home baristas adopt it? I like to think that in many ways home baristas are better than professional ones. It's our hobby, and we go into great detail to achieve the best we can. Well, this is how to do it in my view.








I feel like I'm kinda swimming against the tide of opinion here! That's fine







I'll keep going tho!

Here's a thing... not sure if it will help but here goes.

Anyone who buys good quality espresso equipment and brilliant beans is going to make a less-than-brilliant espresso unless they take the time to learn how to monitor and tweak the relevant parameters. As home baristas we excel at this, I think, and we talk about it a lot. Eventually we are able to produce good espresso fairly consistently, based purely on our taste buds and knowledge of parameters. (However, we could do better.)

On the other hand we rarely talk about monitoring and tweaking parameters when brewing non-espresso drinks. Not because brewed coffee is less popular - actually on this forum I'd say it is possibly more popular than espresso. But still we don't go into such detail as espresso. Why is that? I suggest the reason is that we have watched a few video tutorials on http://www.brewmethods.com then made our coffee a few times, then kinda found a way to make a V60 work for us, or a french press, or an AeroPress. "Hmm, that's nice now", we say. And if we can't get a good coffee from a particular brewing device then we just say "Oh I don't like the AeroPress. It never made a good coffee for me." Isn't this a shame? Using brewing control we can do so much more than this. We can refine our technique with each different brew method/device, and with each new coffee we buy, so that we know exactly how to get a great cup from it, and know exactly which direction to go in when it doesn't taste perfect.

I do go on, eh?









Anyway, there it is. Maybe I'm the geekiest of the geeky for liking things like the brewing control chart and refractometers!! I can't help it


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## lookseehear (Jul 16, 2010)

For me, the benefits of owning one of these would be as a quality control measure in a shop. You can never expect to get a perfect cup every time, so I would say that the best way to express consistency would be to aim to get a cup that is perhaps at least 80% perfect 99% of the time. The only way to do that is by brewing A LOT of cups and having a standard set of criteria to test each cup against.

Tasting only gets you part of the way there though, so using this in conjunction with tasting should allow you to at least cut down some of the variables.

The only issue that I have with using a mojo/refractometer is that surely a 19% extraction can be reached by a combination of overextraction and underextraction, so the numbers don't show the whole story.


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## fatboyslim (Sep 29, 2011)

I read somewhere that different beans and blends are best extracted at different temperatures, we are getting really sad here, so this probably has something to do with the quantity or the type of solids (oils) available in that particular bean/blend.

Could a refractometer therefore help you get the correct brewing temperature for that shot based on a achieving a standardised TDS? Assuming all other factors are consistent (e.g. grind, dose etc)


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## MikeHag (Mar 13, 2011)

> The only issue that I have with using a mojo/refractometer is that surely a 19% extraction can be reached by a combination of overextraction and underextraction, so the numbers don't show the whole story.


Discuss... (!)

In my experience the answer to this is yes... being able to measure your results and achieve a particular TDS and extraction yield are not the whole story. For example, in THIS blog post I put up a video of the same beans extracted using the same brew method (pourover), but using a different technique in one case to avoid the over & under extraction scenario. The results were resounding to me... the better cup was by far the one that didn't involve over & under extraction. A refractometer would not, I believe, highlight this. There are other fundamental flaws in technique that must still be addressed in other ways... (hey - we're discussing pourover tecnhique! Brilliant!!







)



> Could a refractometer therefore help you get the correct brewing temperature for that shot based on a achieving a standardised TDS? Assuming all other factors are consistent (e.g. grind, dose etc)


I don't know, is the answer. If I had one I would tell you







However, if your espresso's TDS, as shown by the refractometer, is low then you have a number of options at your disposal to increase it... one of which is to raise the brew temperature. Therefore theoretically there's your answer!


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## jimbow (Oct 13, 2011)

I think you make a good point Mike.

When learning about coffee or perhaps a new brew method a lot of our advancements are made through trial and error and retrospection i.e. what worked and what didn't and what, if anything, should we do differently next time. For this to work, we need an understanding of our goal and a way of measuring (either quantifiably or qualitively) how our last effort compared to it. One way to understand the goal is to experience the coffee produced by someone else who knows how to brew it properly. I remember the first time I tasted a really good espresso was a revelation to me - for years I had been striving towards the wrong goal.

Once we understand our goal, we can then use taste as our measure to guide our own efforts towards the goal. This in itself requires us to translate what we are tasting into changes in our technique

e.g. tastes sour = under extracted -> adjust grind finer next time.

I see the refractometer and brewing control charts simply as a way of making things quantifiable and therefore absolute and less subjective. This is really helpful while learning especially if there is not someone close by to help you understand your goal.

I actually got a cheap refractometer for Christmas but have not yet had a chance to use it. My model is an analogue, optical device that measures in brix (amount of sugar in solution). I think this specific model is aimed at wine and beer making but I should be able to convert the brix value into TDS using the appropriate formula in the same way as the VST ones.


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## MikeHag (Mar 13, 2011)

Thanks jimbow. Yes, the brix ones seem to be a good next step up after a TDS Meter rather than going right up to the VST one. I know there have been limitations mentioned on Home Barista threads, but there are always limitations and I'm sure you'll get masses of benefit from it.


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## jimbow (Oct 13, 2011)

Thanks Mike.

From my very limited understanding so far it looks like the limitation with brix refractometers is in fact espresso - refractometers can only usually measure dissolved solids and unfortunately (or fortunately depending upon how you look at it!) espresso also contains non-dissolved solids because the metal filter allows these to pass through into the drink. Since most manual brew methods use paper filters I don't believe this is a problem with brew coffee.

I believe VST addressed this limitation for their refractometer by benchmarking and defining profiles for espresso which take into account the non-dissolved solids in the cup too - I think they refer to it as TBS (Total Brew Solids).


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## MikeHag (Mar 13, 2011)

As far as espresso goes, Vince Fedele sent me an email recently including the following:

"In Espresso +/- 0.06% [TDS reasing error tolerance] translates to an Extraction Yield of about +/- 0.5%. This near the threshold of what most cuppers can detect as a change in extraction yield in my experience testing tens of thousands of coffees over the past 3-4 years. To do better in terms of accuracy and precision would cost approx $7500-$12,500 USD for a bench top refractometer with a peltier tray or an $20,000 dehydration oven."

This makes their product seem cheap to me!


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## Ian_G (Nov 10, 2011)

I think you're on to something here Mike. £250 is a fiver a week over a year. Given that there are dozens if not hundreds of different SO's and blends then there is plenty of scope to get good use out of it over the years. This would be especially helpful when dialing in a new coffee. You hear of people not being able to "get" particular coffees and so they drop that coffee/roaster because they got nothing good from the brew. Surely a TDS meter will allow you to judge whether it's the coffee or the barista who is to blame.


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## MikeHag (Mar 13, 2011)

Exactly Ian









For the past few days I have been brewing a Sumatra Mandheling. It hasn't been brewing correctly (or rather, I haven't been brewing it correctly!!). It tasted a bit tarry, too thick, just a very strong black coffee, although using my taste buds alone I couldn't have known whether it was too strong, over-extracted, a bad roast, stale beans, awful Sumatran green bean processing, or God knows what. The TDS Meter readings were 1.62% and then I made the grind coarser and it was still 1.60% on the next one. These indicate an overly concentrated (too strong) brew, based upon the chart shown above. Today I adjusted my pouring technique (no change to any other parameters) and it came in at 1.37% (and an extraction yield of 21.9% - right in the IDEAL zone on the chart) and it honestly tasted fantastic... bold yet complex, low acidity and a beautiful chocolatey flavour that is still in my mouth right now. Exactly as the roaster's website said, and to be honest one of the nicest cups I've ever had... even though the beans were roasted before Christmas! If I hadn't known about measuring my extractions I would have probably binned the beans... what a disaster! Awesome beans completely wasted!!

After that I switched to a Tanzanian single origin and used exactly the same parameters (grind, dose, brew time etc) and same pouring technique. Guess what... it tasted crap! Was it the beans? No. I'm confident that it is all my own fault because I haven't yet dialed in these beans for a controlled manual brew (i.e. dialed in MYSELF to brew these particular beans).

TDS Meter: £40-50 (brewed coffee only)

Brix Refractometer £100-ish (brewed coffee only)

VST Coffee Refractometer £250-ish (capable of measuring brewed coffee and espresso)

(You can always start with the TDS Meter and upgrade later)

I heartily recommend reading Scott Rao's book if you're interested in taking this further. It's the bible of non-espresso brewing.

(Now I must reiterate that there are known accuracy issues with a TDS Meter and there are calculation/conversion challenges with 'brix' refractometers that aren't specifically designed for use in measuring coffee. These issues are not insurmountable though, and as I'm finding, they are all a step in the right direction for we baristas.)


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## Monkey_Devil (Jul 11, 2011)

Not got much to contribute here, since it does indeed get too geeky for me - i simply don't have the perseverance haha. However, i saw this at Cream Supplies and remembered this thread.

Refractometer for £180. There may be a reason its cheaper or it may have less functionality etc, so I'll leave that to people like mike to check out. Just thought I'd point it out.

http://www.creamsupplies.co.uk/digital-refractometer/prod_5479.html?category=279


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## radish (Nov 20, 2011)

I have the VST Coffee refractometer (with PC based ExtractMojo software for brew and MojoToGo app for espresso). If any Scottish members are interested I'd be happy to let folks have a play sometime.


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## MikeHag (Mar 13, 2011)

Oh blimey. Is it my birthday? Where are you based?







One thing I'd love to do is compare readings with the COM-100 TDS meter.


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## Glenn (Jun 14, 2008)

Sorry it has taken me so long to notice this thread and reply. I have been working behind the scenes to get the UKBC off to a flying start this year.

I was an early adopter of the VST Refractometer and ExtractMoJo having gained accreditation as an SCAE Brewmaster Level 1 in October 2009

It's vitally important to point out that taste should be the first consideration when using any coffee related tools

However, the use of a refractometer (or even a TDS meter) and charts (or even charting apps/software) can help you understand how to get even more out of the coffee and also how to correct any faults in your brewing method.

Using these tools allows you to get consistent results when bulk brewing and also allows you get gain a deeper understanding of the factors that influence taste - these are (contact) time, temperature and turbulence.

I could spend hours talking about this subject (and playing with brewing variables) and would certainly also be open to leasing out my refractometer when not required as well.

The ExtractMojo App is a scalable module allowing you to buy calculation modules for Brewed Coffee and also Espresso as well

It works fantastically well and helped improve my understanding through its visual nature. It also makes explaining brewing logic easy to people just starting down the brewed coffee path.

I think there should be a brewed coffee section of Coffee Forums UK and will set this up over the next few days - where we can share information and brewing techniques that a lot of people will probably find quite helpful.

Some related blog posts:

http://5mcoffee.com/coffeeblog/index.php/gold-cup-accreditation/

http://5mcoffee.com/coffeeblog/index.php/mojo-goes-mobile/

The SCAE website also has a Gold Cup section, which is being updated with a whole new coffee research project already underway to see if the theories from the 1950s still stack up, and how we can apply what we now know, to brew even better and more consistently in the future.


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## fatboyslim (Sep 29, 2011)

http://www.ebay.co.uk/itm/Brix-Refractometer-0-18-Brix-RHB-18TAC-Used-/150730440665?pt=Home_Brew&hash=item23183bffd9#ht_761wt_1396

Is this the sort of thing you have GlennV?

Being a food scientist, this sort of thing interests me great but I can't justify the funds for a VST refractometer.


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## takingabreak (Nov 10, 2011)

Yes, the same model number even. There's also a 0-10%, which would be a bit more appropriate for brewed coffee.


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## MikeHag (Mar 13, 2011)

Glenn said:


> The SCAE website also has a Gold Cup section, which is being updated with a whole new coffee research project already underway to see if the theories from the 1950s still stack up, and how we can apply what we now know, to brew even better and more consistently in the future.


Looking forward to getting a clearer picture of the SCAE education programme soon. Things seem to be in a state of flux at the moment, which makes it difficult to decide which courses to invest in.



GlennV said:


> I think there's something wrong in the accuracy numbers given a few posts back by the way. It is a little ambiguous talking about percentage errors in numbers which are themselves percentages, but I can't see any interpretation in which a 0.06% error in tds would give a 0.5% error in yield. A 0.06% error in the tds reading (by which I mean 12.06% vs 12%, not 0.06% of 12%, for example) actually corresponds to a an error of 0.1% in extraction yield for espresso brewed at a 60% brew ratio (ie 20.1% vs 20%) - which is probably not tastable, certainly not by me. However, the same error in tds would give an error of about 0.9% in extraction yield for brewed coffee at 60g/litre - which is massive, and illustrates why it's a lot harder to measure yield in brewed coffee.


The brewing log I've knocked up in excel (using the formula from Rao's book) does indeed show drip coffee's +/-0.06% TDS error resulting in +/-0.95% variance in Ext% (which agrees with another section of Vince's email), but I don't have an espresso-specific formula and would have to take your word on it that perhaps there's an anomaly in his statement. Typo maybe. But the reason I contacted him in the first place was to get a better understanding of the error tolerances, since +/-0.06% TDS error did seem quite a large window to me... there's going to be a big difference in taste between a TDS of 1.20% and 1.32%. In his response he basically says that although technically this is the case, in practise the margin of error is smaller than that, as the devices are tested/referenced against a reference solution that itself is warranted to "+/- 0.01 to 0.02%" (although I think this is for the LAB model, and the £250 STD model is perhaps likely to be +/- 0.03 to 0.04%). So that makes the likely Ext% error more like +/-0.06% than 0.095%. That closes the error window a little, and every little helps!

*I suspect this numerical interlude may have scared a few people off!! Please don't run, folks *







* Brewing control is absolutely not as technical as this might make it seem. As GlennV says, it's just a case of taking a reading and letting the device do its thing. I'm certainly no expert, but if I can shed any more light on it for anyone then please ask away *









*
*


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## jimbow (Oct 13, 2011)

Here is the post that first drew me to using a brix refractometer. It was posted by Alan Alder on his experiences using a brix refractometer to measure coffee strength whilst developing the Aeropress and includes the formula he used to convert between brix and TDS.

http://scientificgear.net/wordpress/2008/08/measuring-coffee-strength-with-a-brix-meter/


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## MikeHag (Mar 13, 2011)

The actor from M*A*S*H*?? OK, I guess not









That's a good little article to get started.


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## MikeHag (Mar 13, 2011)

By the way, where's a good place to buy the VST packages in the UK? Or do they just need to be bought and shipped from the US?


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## radish (Nov 20, 2011)

MikeHag said:


> Oh blimey. Is it my birthday? Where are you based?
> 
> 
> 
> ...


I'm from Hamilton (just outside Glasgow).


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## DonRJ (Apr 3, 2010)

I have a refractometer and TDS meter and will not be using them to measure my coffee. why?

1. TDS measurement is only useful if you have a consistent baseline measurement to start from - eg zero which you will only get from pure reverse osmosis water which I do not want to drink but is great for my marine salt preparation. If I check TDS of my water from the tap it varies between 370 and 450, I bet Mikes TDS in Perthshire is very low in comparison, too much variability over time and geographically for any sort of proper scientific analysis.

2.There is a direct relationship between refractive index and TDS, so any measurements are again skewed by the baseline TDS of the water used to brew the coffee.


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## jimbow (Oct 13, 2011)

GlennV said:


> ...
> 
> For espresso this works well - for brewed coffee you're only going to get a pretty rough idea of extraction yield using a brix refractometer.


Interesting. Do you know why this is? Everything I had read pointed to the opposite i.e. that measuring with a basic refractometer worked most accurately for brewed coffee and got close for espresso. The reasoning seemed to be that espresso has non-dissolved solids in addition to the dissolved solids measurable with a basic refractometer. In contrast, brewed coffee only has dissolved solids because the paper filters used prevent the non-dissolved solids and other matter from passing through into the cup.


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## MikeHag (Mar 13, 2011)

Don,

Please correct me if I am wrong but surely the baseline water TDS is easy to adjust for, isn't it? If the water is 400 ppm and the coffee is 13500 ppm (1.35%) then you subtract and get a coffee TDS of 13100. It makes no difference if your water is different from mine since we just each subtract a different number.


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## Glenn (Jun 14, 2008)

Purified water from a chemist can be used to calibrate the refractometer.


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## DonRJ (Apr 3, 2010)

> Don,
> 
> Please correct me if I am wrong but surely the baseline water TDS is easy to adjust for, isn't it? If the water is 400 ppm and the coffee is 13500 ppm (1.35%) then you subtract and get a coffee TDS of 13100. It makes no difference if your water is different from mine since we just each subtract a different number.


You are right Mike, the problem that would reduce the accuracy for the likes of me is that the TDS varies markedly over time and I would be forever recalculating which seems a faff for the possible benefits. Due to keeping reef aquariums I am constantly monitoring my water which is very hard locally and have encountered a range between low 300`s and high 400`s before treatment to take the TDS to zero.

I guess I am not into that level of scrutiny of my espresso production and another thought would their be marked differences between results dependent on the beans used. I fear that would mess with my head a bit too much. even my OCD cries enough.


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## jimbow (Oct 13, 2011)

I have had a couple of attempts at V60 pour overs using a refractometer now and have some questions regarding brew ratios, extraction and the brewing control chart I am hoping you guys might be able to help with.

1. I am working off the principle that brew ratios for brewed coffee use the brew water rather than the mass of the beverage as with espresso, is this correct?

2. I have been calculating extraction % as the TDS% * brew water / coffee dose. Logically this should give the extraction but looking at the SCAE brewing control chart I notice that it gives me a different value for the same TDS and brew ratio. Does this difference simply account for the brew water absorbed by the grounds and the TDS in that water or am I missing something?

Thanks in advance for your help.


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## MikeHag (Mar 13, 2011)

Hi jimbow.

1. Yes

2. Need to check that I understand what you mean so a link to the version of the chart you're looking at along with numbers could be good. But in the meantime I'd just make sure you are looking at apples and apples. Often the chart has g per litre rather than g per unit of weight (g). Could that be what's causing the diff? Bear in mind that 1000g of water and 1000ml of water are not the same at all temperatures.


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## MikeHag (Mar 13, 2011)

Must admit I have been using brew water weight rather than beverage weight to calculate my Ext %, and haven't adjusted for water retention/absorbtion. Disappointed with myself! Will start using true brewed mass (beverage weight) rather than water mass from today.

Here's a link to a template of my manual brewing log. I'm sure you can follow the formulae. I plug in the weights, and then the TDS reading, and it calculates the Ext %. I also have it set up to show whether the Ext % is between 18-22%, and TDS is between 1.15-1.45% (columns R to T). Funnily enough I use it to control my brews







Not much point in assessing a coffee if I haven't brewed it 'correctly'.

http://www.box.com/s/hv3ahh3fyrsyf0yiarev


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## jimbow (Oct 13, 2011)

Thanks Mike and Glenn. I have in fact been working on a similar brew log myself and the reason for my question was to correct the extraction formula in the log. I wanted to confirm whether there was a generalised formula or whether I needed to extrapolate one using data points on the brewing control chart.


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## jimbow (Oct 13, 2011)

So I used the refractometer this morning with my V60 brew and calculated the yield using a number of different formulas, tools and charts and thought I would share the results with everyone. I should point out in advance that I was using a new coffee and still getting to grips with the V60, dialling in the grinder, etc. (I know; excuses, excuses ;-)) and the resulting brew was weak and under extracted.

Grounds: 15g

Brew Water: 255g

Beverage: 223g

TDS: 1.02% (too weak)

Extractions:

TDS% * Brew Water / Grounds = 17.34% (using brew water weight)

TDS% * (Brew Water - (Grounds * 2)) / Grounds = 15.3% (accounting for brew water retained in spent grounds - thanks to GlennV for this)

TDS% * Beverage / Grounds = 15.164% (using beverage weight)

MojoToGo extraction = 15.46%

Brewing Control Chart = 15.59%

I am not sure what formula the MojoToGo application is using to calculate the extraction but I am surprised that the result does not correlate directly with any of the others given it uses the same input data. However, I am not sure how much material difference a 0.3% deviation makes in practice.


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## MikeHag (Mar 13, 2011)

Excellent, jimbow







Really great to read this. If your experience is anything like mine then this is going to be a whole new chapter for you. It was a bit of a shock for me when I started measuring extraction, having thought I was doing everything correct until then and suddenly finding that MOST of my brews were either under or over extracted. Expect coffees to get better and better from now on... and also frustrating moments when you just can't hit the target







 Exciting stuff IMHO.

No idea why there might be a difference with the Mojo app. Possible they have built in further adjustments to the formulae.


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## Fran (Dec 27, 2010)

This refractometer malarkey is really exciting. I think I might have to get involved. Problem is that I don't have any time to experiment! I only just about have time to make a coffee before work!


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## jimbow (Oct 13, 2011)

GlennV said:


> OK. So it appears that MojoToGo accounts for the mass of the dissolved coffee solids in its estimate of the beverage weight, ie
> 
> (Brew Water - Grounds * 2 +Grounds * yield%/100)
> 
> ...


Thanks Glenn, at the moment I am converting from Brix to TDS using a factor of 0.85 which is where the second decimal place is coming from. I have extrapolated a generalised formula through polynomial regression from the brix/nD table you pointed at so might start using that with MojoToGo to calculate TDS going forwards. It will be interesting to see how the two methods compare.

Interestingly I found the factor of 2 (water retention to grounds) fairly accurate - it was out by only 2g from the actual measured beverage weight.


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## MikeHag (Mar 13, 2011)

GlennV and jimbow, this discussion has thrown up huge implications for the measurement of my brews (and means that brew log template I posted needs to be updated). If I recalculate the Ext % of my logged brews using this new formula it results in a difference of around 2.5% on average. That is massive, taste-wise. It does explain a few things... for example I think that most of the logged brews I've enjoyed the most were previously showing Ext % at the higher end of the 18-22 range, and sometimes slightly beyond that... for example, a really nice chocolatey mandheling was showing 21.9%... but if the new formula is used and is credible then in reality the ext % was 19.1%.

I am going to assume it is indeed a credible formula, since a brew I just performed resulted in the following:

- Initial formula, using brew water weight rather than beverage weight: *19.1%*

- New formula, taking into account adustments for likely water retention in grinds: *16.6%*

- MojoToGo: *16.8%*

Loving this. Thanks for helping through discussion.


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## MikeHag (Mar 13, 2011)

For me, one of the best things gained from understanding controlled brewing is that after dialing in the coffee beans, I can then (hopefully!) decide how to brew it. Which parameters I think will work best for that particular coffee on that particluar day. Is it better as a strong coffee (high TDS)? Should I avoid a high extraction because this coffee tastes better at a lower extraction?

To illustrate this, see the table below. Sometimes is can be difficult to understand such tables at a glance, so here's some of what it shows. Remember that the 'ideal' TDS is 1.15-1.45% (see note (i) below), and the 'ideal' Ext % is 18-22%:

- 20 theoretical brews (brewed coffee, not espresso).

- The cup size is always the same, so the water dose is always 211g.

- The 20 brews are split into 4 groups of 5. Each group of 5 shows the same coffee, at the same strength (i.e. same TDS), but at 5 different dose weights of grinds. This shows the effect of dose upon the Extraction Yield (Ext %). As you decrease the dose of grinds, but end up with the same sized cup of coffee at the same strength, then to achieve that strength you must have extracted 'coffee' more from the coffee grinds you have in the brewing device. (I'm trying to keep this as uncomplicated as possible, for anyone who hasn't read Rao's book yet) So each row represents the change in dose needed to make a 1% change in Ext%, and the five rows represent the 18-22% Ext % that is 'ideal'. As you *decrease *the dose of grinds, if all other factors remain equal then your Ext % will *increase* (and vice versa).

- OK, but what happens if you make the brew stronger... i.e. a higher TDS? This is why there are 4 groups. each group has a different TDS, starting at 1.15% and rising in steps to 1.27%, 1.35% and ending at 1.45%. This range encompasses the 'ideal' TDS zone that the speciality coffee bodies identified through their research.

- There are also two columns for Brew Ratio, expressed in two of the popular ways... the ratio of water to grinds (e.g. 16:1), and also expressed as grammes per Litre (e.g. 60g/L).










What can we learn from this? Here are just a few observations... I hope you will come up with more of your own!:

1. Look at cells 060 and P60. Often people will talk about using a brewing ratio of 16:1 or 60g/L. But hang on.... this brew has successfully achieved 'ideal' status... it will potentially be a good coffee... yet the brewing ratio is radically different, at a ratio 21.1:1 or just 47g/L. Infact, if you had used 60g/L for this coffee, and achieved an acceptable strength of 1.15% (like this one), you would actually have produced a coffee that is underextrated according to the brewing controls. It would have had an Ext % of only 17%, and would therefore have quite possibly tasted sour. And you would probably have wondered why, and perhaps wrongly dismissed the coffee as being horrible! *So this fact speaks for itself... using 60g/L is not always the right thing to do*. It is merely terminology that people have used to make it easier to communicate brewing ratios.

2. This cup of coffee is always the same size. However, we can make that coffee taste many different ways, and still have it successfully fall into the 'ideal' zone. We could use a minimum dose of 10g, or we could use a maximum dose of 14.6g. That's a *big *difference in the amount of grinds in there, and this is reflected in the Extraction %. At 10g (ii) the Ext % is 22%, whereas at 14g the Ext % is 18%. These two will taste completely different, yet both are still in the 'ideal' zone as per the standards. *As baristas we should be (and now are!) capable of making a decision regarding which of these different tastes we want to produce when we brew a particular coffee. *We are in charge, the coffee is not in charge of us (iii).

These are just a few of my thoughts. I think they are correct but I'm also keen to hear any thoughts, as I'm like you... I'm learning. Always.

*Notes:*

(i) This TDS range is a composite of the SCAA, SCAE and Nordic brewing control standards.

(ii) ... and the appropriate strength

(iii) However, being able to set targets and subsequently measure the brew does not mean we can automatically get it right. There are still skills to be learned, otherwise we will not be able to hit the target.


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## jimbow (Oct 13, 2011)

Thanks again Glenn and Mike, this has really been helping me get to grips with measuring my brews and understanding the V60. I must admit I picked up my new pouring kettle today and wow what a difference it makes!

If anyone is interested, I have put my brew log updated with formulas discussed here (including Brix to nD conversion) on GoogleDocs:

https://docs.google.com/open?id=0B1utbbP3laRJZGQyZTY0NmQtNDdjNC00MDUzLWI2ZWUtNGMxYjk0N2MxMjJk

Measuring the extractions has added a whole other dimension to brewing for me and really helped me tie up what I am tasting with what is really going on in the brewing process.


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## MikeHag (Mar 13, 2011)

Thought it might be worth putting this little video from my blog on here...


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## jimbow (Oct 13, 2011)

Is that a Chemex in the background Mike? How are you finding it?


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## MikeHag (Mar 13, 2011)

Yes, 4-6 cup. It's absolutely great. Everyone always said what a clean cup you get and it's true... flavours are so crisp. And I love having a big portion too... so great when we have guests. You have one?


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## jimbow (Oct 13, 2011)

Unfortunately it is something I still have yet to try







I have been eying it up on the HasBean website every time I order more beans but have not gotten around to making the purchase. A situation that I will have to remedy!


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## MonkeyHarris (Dec 3, 2010)

Excellent video Mike. Very informative.


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## Earlepap (Jan 8, 2012)

I put a chemex on my hasbean order with a grinder - can't wait. Currently awol in post-land it seems.


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## brun (Dec 26, 2011)

All my post has been 3+ days recently


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## MikeHag (Mar 13, 2011)

For me a great bonus with the 4-6 cup chemex is that fewer beans get wasted. In the past I've always bought too many different bags and ended up binning some of them.


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## fatboyslim (Sep 29, 2011)

Great video and looks like a great bit of kit but no way I could justify the cost.

I'll hopefully be back in a lab soon with many a photo-spectrometer so if anyone knows what wavelength of light coffee (or perhaps one specific component in coffee) absorbs or emits in I'll be able to play around with working out very accurate concentrations.

Would be fun to compare results


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## jimbow (Oct 13, 2011)

So tempted by a VST refractometer now!









With the Chemex, what is the smallest quantity of coffee you brew with the 3-6 cup version?


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## MikeHag (Mar 13, 2011)

3 cups
















I haven't had it long so I haven't used a lot of parameters. I believe by Hario standards 1 cup is 150ml, and that would mean you can get 900ml in the chemex (6x150ml) but around 700 seems to be the max... so by inference you could possible brew about 350ml min if you wanted... or grab a 1-3 cup chemex instead/too.


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## Glenn (Jun 14, 2008)

Following a request from a member, a number of their posts discussing the use of a Brix refractometer for coffee have been removed

This thread has now been locked and a new thread should be created to start the conversation again.

It is very rare that these requests are received but we try, where possible, to ensure all details are factual and that the interests of all parties are considered before removing any posts.


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