# Refractometer



## aphelion (Nov 23, 2012)

Just wondering what the latest consensus is on these?

I would love a VST Lab II, but at £500+ they are looking pretty steep these days!

I know there are a few cheaper options, but is there anything else worth considering?

Cheers


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## Glenn (Jun 14, 2008)

If you're using to measure TDS of brewed coffee then you can use a TDS meter (approx £15) and perform some simple calculations (eg total TDS less the TDS in the water)

Not as easy for espresso, where a refractometer makes the process infinitely easier


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## aphelion (Nov 23, 2012)

Thanks Glenn,

I notice creamsupplies have a couple of kits (brewed and espresso) - dunno how useful they will be?

Do you think a TDS meter would be accurate enough?

Would ultimately like something that does both brewed and espresso..those VSTs do look great


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## Glenn (Jun 14, 2008)

Yes, TDS definitely accurate enough for brewed coffee.

Our SCAE Brewmaster Course was conducted using TDS meters and our results compared against using Refractometers (which only a couple of years ago was new technology)

When used properly the results were accurate against the Refractometers. eg You need to measure at consistent temperature levels


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## aphelion (Nov 23, 2012)

Great, so something like a com-100 would be perfect for brewed? (measured at room temperature)


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## Glenn (Jun 14, 2008)

My first TDS before getting a Refractometer was http://www.tdsmeter.co.uk/products/tds3.html

CoffeeHit sell this one http://www.coffeehit.co.uk/hm-tds-reader/p1053

Creamsupplies sell this one http://www.creamsupplies.co.uk/total-dissolved-solids-tds-meter-low-volume-0-9990-ppm-/prod_6331.html?category=

All will work for brewed coffee


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## Sam__G (Sep 4, 2011)

Glenn said:


> Yes, TDS definitely accurate enough for brewed coffee.
> 
> Our SCAE Brewmaster Course was conducted using TDS meters and our results compared against using Refractometers (which only a couple of years ago was new technology)
> 
> When used properly the results were accurate against the Refractometers. eg You need to measure at consistent temperature levels


Is there an ideal temperature to measure at or is it just about being consistent?

I've got a TDS meter (looks pretty similar to the CreamSupplies one, though I think it was a little more expensive...) but haven't persevered with it for long enough to get useful information from it. I bought it when MikeHag became big into measuring his brewed results but gave up when I realised he seemed to have become much more bothered about extraction than taste!


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## AndyS (May 12, 2012)

Glenn said:


> My first TDS before getting a Refractometer was http://www.tdsmeter.co.uk/products/tds3.html
> 
> CoffeeHit sell this one http://www.coffeehit.co.uk/hm-tds-reader/p1053
> 
> ...


What refractometer do you have? Is it calibrated for coffee?

It would be interesting to see direct comparisons of refractometer coffee measurements vs your TDS meter.

Measuring coffee with TDS meters is a mysterious process of unknown accuracy considering:

1. Typical brewed coffee TDS is ~1.3% or 13,000 ppm

2. Your TDS meter cited above has a range of 0-9990 ppm

3. Your TDS meter is calibrated for sodium chloride

4. Supposedly dissolved coffee is about 1/10th as conductive as NaCl, but this ratio is said to vary with roast, water, etc.

5. The conductivity meter manufacturers often warrant their instruments for accuracy when measuring dissolved minerals, but not for coffee.


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## Glenn (Jun 14, 2008)

My refractometer is a VST Coffee refractometer.

I sold my TDS as soon as I purchased the refractometer, about 5 days after my brewmaster course.

Whilst a TDS meter is not as accurate, a refractometer is out of reach for most home users.

They are still an effective tool in measuring TDS in brewed coffee


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## AndyS (May 12, 2012)

Glenn said:


> Whilst a TDS meter is not as accurate, a refractometer is out of reach for most home users.
> 
> They are still an effective tool in measuring TDS in brewed coffee


It is likely that TDS meters are effective for measuring relative strength, eg, "cup A is stronger than cup B." With proper protocol, this could be extended to make relative extraction yield comparisons, eg, "coffee A was extracted to a higher yield than coffee B." But we would need a lot more evidence to conclude that TDS meters can make useful measurements of absolute extraction yield, eg, "coffee A was extracted at 19%."


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## Glenn (Jun 14, 2008)

You need to know the dry weight and end weight (volume) in conjunction with the TDS reading to get the extraction ratio.

On its own the TDS reading doesn't tell you anything.

You can recalibrate the TDS meters


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## AndyS (May 12, 2012)

Glenn said:


> You can recalibrate the TDS meters


Yes, but if you don't have a coffee refractometer or a dehydration oven, to what standard do you recalibrate?


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## MWJB (Feb 28, 2012)

AndyS said:


> Yes, but if you don't have a coffee refractometer or a dehydration oven, to what standard do you recalibrate?


AndyS, calibration (which can be a thorny subject in any test & measurement sphere) apart, do you not think there is any benefit in measuring an identifiable & relative (even if only relative to one home-barista's immediate environment) datum? I mean in terms of determining a scale, whether those numbers correlate precisely to genuine extraction yield %/g, or not? In many cases, especially, where there may be conflicting ideas of how measurement & analysis is performed, it becomes more important in the real world/field to be able to perform a test the same way, in a repeatable manner & correlate that to a result? E.g. if I took TDS readings (even without a conversion formula) & discovered a number that translated to a "good cup", whether it be "1", "10" or "100" and even if it related to a different scale for each brewer used, wouldn't that be of some value to the individual?

After all, even the Extractmojo (though undoubtedly the leader in this field) relies on algorithms & assumed water retention in the grinds, to back calculate yield for brewed coffee (already been revised once, probably will be optimised again in due time). How does it deal with brewed methods with a relatively high undissolved solids content (Sowden, Kone, etc) & brew methods that may result in a difference in TDS from one end of the brew to the other?

The Cream Supplies TDS meters do read in a range that will "work" for coffee (the other links posted seem to point to devices best used for water analysis).

Not trying to poke any holes in the Extractmojo, nor suggest that a £20 TDS meter is a serious alternative to an Extractmojo, just looking at it from the perspective of whether the more basic tools can provide at least some context of assessing consistency when brewing, for the average home user?


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## AndyS (May 12, 2012)

MWJB said:


> AndyS, calibration (which can be a thorny subject in any test & measurement sphere) apart, do you not think there is any benefit in measuring an identifiable & relative (even if only relative to one home-barista's immediate environment) datum? I mean in terms of determining a scale, whether those numbers correlate precisely to genuine extraction yield %/g, or not? In many cases, especially, where there may be conflicting ideas of how measurement & analysis is performed, it becomes more important in the real world/field to be able to perform a test the same way, in a repeatable manner & correlate that to a result? E.g. if I took TDS readings (even without a conversion formula) & discovered a number that translated to a "good cup", whether it be "1", "10" or "100" and even if it related to a different scale for each brewer used, wouldn't that be of some value to the individual?


I think that's true: for one's own personal brewing, any arbitrary measurement scale that correlates with one's personal taste can be of value. However, I believe that sharing of our experiences, techniques and measurements (such as on this forum) has been key in recent coffee quality advances. So repeatable, accurate, universal measurements that can be communicated worldwide seem far, far more useful to me than systems that are individual to each person. If you're in the UK and I'm in the US, we can't effectively share notes unless we have a universal coffee language.



MWJB said:


> ...the Extractmojo (though undoubtedly the leader in this field) relies on algorithms & assumed water retention in the grinds, to back calculate yield for brewed coffee (already been revised once, probably will be optimised again in due time). How does it deal with brewed methods with a relatively high undissolved solids content (Sowden, Kone, etc) & brew methods that may result in a difference in TDS from one end of the brew to the other?


The VST software does not *rely* on water retention assumptions. You have the option to bypass that feature, weigh the outputted beverage, and enter that number directly. If that procedure is too inconvenient, though, one can skip weighing the beverage, use an assumed water retention ratio, and still get a pretty good calculation via the assumption.

VST makes a distinction between Total Brew Solids (TBS), Total Undissolved Solids (TUS) and Total Dissolved Solids (TDS). TBS = TUS + TDS.

TUS is correlated mostly with mouthfeel, not flavor, and is not counted in the Extraction Yield calculation. TDS is correlated with flavor; it is what the refractometer measures and is one of the key measures in calculating Extraction Yield. Methods with high TUS (eg, metal-filtered coffee) generally need additional filtering before being measured.

I don't think it matters that there is a "difference in TDS from one end of the brew to the other." Extraction yield calcs use the whole thing.



MWJB said:


> Not trying to poke any holes in the Extractmojo, nor suggest that a £20 TDS meter is a serious alternative to an Extractmojo, just looking at it from the perspective of whether the more basic tools can provide at least some context of assessing consistency when brewing, for the average home user?


I wouldn't want to discourage anyone from using inexpensive tools to improve their beverage; they should just understand the limitations of whatever system they're using.


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## aphelion (Nov 23, 2012)

Glenn said:


> You need to know the dry weight and end weight (volume) in conjunction with the TDS reading to get the extraction ratio.
> 
> On its own the TDS reading doesn't tell you anything.
> 
> You can recalibrate the TDS meters


Got me a meter today..

Questions:-

1) Do I need to divide the dry weight (ground coffee) by the end weight (liquid coffee)?

2) Can I put the meter into a small amount of the brewed liquid to take the TDS reading? (or does it need to be the full amount brewed?)

Cheers


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## AndyS (May 12, 2012)

aphelion said:


> Got me a meter today..
> 
> Questions:-
> 
> ...


1) Extraction Yield (for drip methods or espresso) = (beverage weight) x (%TDS) / (dry coffee weight)

2) Small amount is OK as long as it is representative of the whole (stir well before taking sample)


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## aphelion (Nov 23, 2012)

AndyS said:


> 1) Extraction Yield (for drip methods or espresso) = (beverage weight) x (%TDS) / (dry coffee weight)
> 
> 2) Small amount is OK as long as it is representative of the whole (stir well before taking sample)


Thanks AndyS..

Sorry for being dense, where do I get that (%TDS) figure from?









Is this the TDS reading - e.g. 1.25?

e.g. (200g beverage weight x 1.25) / 15g dry coffee weight

Cheers


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## Torbj0rn (Nov 4, 2019)

AndyS said:


> I think that's true: for one's own personal brewing, any arbitrary measurement scale that correlates with one's personal taste can be of value. However, I believe that sharing of our experiences, techniques and measurements (such as on this forum) has been key in recent coffee quality advances. So repeatable, accurate, universal measurements that can be communicated worldwide seem far, far more useful to me than systems that are individual to each person. If you're in the UK and I'm in the US, we can't effectively share notes unless we have a universal coffee language.
> 
> ...
> 
> I wouldn't want to discourage anyone from using inexpensive tools to improve their beverage; they should just understand the limitations of whatever system they're using.


 I agree with you there, but a VST refractormeter is very expensive for the most home brewers. Today you can get cheaper options from china for 1/7 of the cost (<$100).

Have anyone tested these and compered to a traditional VST? If the error margin is within a certain level, for my personal use would be OK with that.


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