# Comparison of Atago Pal Coffee TDS with cheap £40 HM Com-100 conductivity meter7



## Stevebee (Jul 21, 2015)

I recently got hold of an Atago Pal Coffee TDS in order to look at extraction yields of my brewed coffee. I already had a cheap conductivity meter, a £40 ish HM EC/TDS/TEMP COM-100 bought from Amazon so out of curiosity I tested 4 of my brews plus for fun, 2 espressos.

As the Com-100 contacts need to be submerged in the coffee I used a shot glass to test. The sample for the Atago was taken from this glass as well, which was allowed to cool down to 20-25c so that the coffee was close to the device temperature.

One brewed sample, was watered down with a known qty of water to and tested as BREW4

Also two espresso were done, one measured as is, one filtered via a dry V60 paper as I don't have the specialist filters.

Below are the results

___________ATAGO. _______COM-100

_______TDS. ___EY. ______TDS. ___EY

BREW1. 0.87%. 13.65%. ___0.89% 13.96%

BREW2. 1.41%. 19.96%. ___1.40% 19.82%

BREW3. 1.35%. 19.32%. ___1.39%. 19.89%

BREW4. 0.63%. 17.37%. ___0.69% 19.03% (WATERED)

______________Atago_____________Com-100

ESPRESSO_____TDS____EY_______TDS____EY

1 UNFILTERED. 12.04% 19.22% ___6.33%. 10.11%

1 FILTERED. 12.27%. 19.59%. __6.27%. 10.01%

2 UNFILTERED. 12.51%. 22.17%. __7.30%. 12.94%

2 FILTERED. 12.10%. 21.44%. __7.05%. 12.48%

I didn't expect the Com-100 to be close to the Atago in the brewed range. However, for espresso I think the numbers are so far out from what is designed for that the only way you might get reasonable measures is to do a controlled dilution to bring the TDS number more in range. I may try this later to see if it makes a difference.

I will continue to measure my brews with both machines to see if this pattern continues. If it does, then it might be a cheap way to get measuring extraction yields as long as the variances are within your own personal tolerances.

After a while I'm sure I can see how close the Com-100 is but probably only use it when the Atago is not around.


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## MWJB (Feb 28, 2012)

People had been trying to use conductivity meters for years before the coffee refractometer became available, the excursions in readings are far too variable to be useful with regards to determining EY. I did like you & measured both ways when I got my VST refractometer, but it didn't take long to see that readings were so diverse that I couldn't have any confidence that my brews were landing in a useful range with the conductivity meter.

If you have a reasonable protocol, then for similar methods it might tell you which brews are stonger/weaker, more/less developed, compared to each other, which may be useful to you. But it won't mean much to anyone else (EY isn't just a formula, it's a correlation to a mass ascertained by dehydration). Plus you waste a fair chunk of a brew with the conductivity meter.

Take 10 readings from both devices, of the same sample, for your next tests, see how they vary over the time it takes to read them off/stabilise.


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## Stevebee (Jul 21, 2015)

I didn't take 10 but 4 or 5 readings from the same sample. Generally within .01 or .02 with 2 or 3 the same. It may have helped that sample was virtually the same temp as the unit so less adjusting for temp going on.

With the Com-100 I think it is definately necessary not to use a warm sample as the initially reading is way different than the final settled one.

I was using about 20ml of my brew, which for pourover was fine re waste as I make for 2 cups anyway

I've seen comments that the the conductivity meter is not accurate enough to get a reliable Extraction Yield hence why I did the tests and was surprised how close they were, even when converted to the yield.

I will, as it's not onerous and I'm doing the refractometer readings anyway, continue to do both to see if this small sample was not reflective of what will be shown in the long run as the 3 brews I tested were within 0.5% extraction yield.


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## Stevebee (Jul 21, 2015)

Sorry, meant to attach a photo of the TDS meter I was talking about, HM Com-100


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## MWJB (Feb 28, 2012)

Stevebee said:


> I've seen comments that the the conductivity meter is not accurate enough to get a reliable Extraction Yield hence why I did the tests and was surprised how close they were, even when converted to the yield.
> 
> I will, as it's not onerous and I'm doing the refractometer readings anyway, continue to do both to see if this small sample was not reflective of what will be shown in the long run as the 3 brews I tested were within 0.5% extraction yield.


Well, the TDS reading you see will be relative to the EY in closeness, because you use the reading to calculate an EY value. But you don't really know how they relate to extraction yield as you have no datum (Atago & VST provide accuracy specs for their refractometers). You can only observe the repeatability (precision) of the readings, if the Com 100 is +/-0.5%"EY" off the Atago for brewed, then your repeatability is already likely +/-1%EY, this is where the problem lies...you can't convert, or correlate precision (accuracy is another matter & not something that will be easy for you to ascertain).

Nevertheless, have fun with it & 10 readings would be the minimum you'd really do to get a meaningful insight, though that many readings quickly becomes inversely proportional to the fun aspect!


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## Stevebee (Jul 21, 2015)

I might try more samples (unless I get bored!) and see what pattern emerges. It might in the long run turn out as you said and offer a number that can't be relied on. I will be using the Atago number anyway but after seeing the initial tests was thinking it might be a cheaper way to get a ballpark EY figure. Probably won't be the case but I'll do a few more tests anyway  (but not for espresso!)


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