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Discussions > Coffee > Machines > TDS & Distilled...  
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kolu
Senior Member
kolu
Joined: 28 May 2013
Posts: 29
Location: Reykjavík, Iceland
Expertise: Pro Barista

Espresso: Grimac La Uno
Grinder: Mahlkönig Guatemala, Porlex
Drip: Kalita Wave, Aeropress
Posted Mon Jan 13, 2014, 8:53pm
Subject: Re: TDS & Distilled Water
 

Yes, that's basically what I'm trying to do at home now. But just on a one coffee-per-day basis so I'll probably do more intensive testing.

Thanks again for your help, Andy.
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jpender
Senior Member
jpender
Joined: 11 Jul 2011
Posts: 708
Location: California
Expertise: I like coffee

Grinder: OE LIDO
Vac Pot: S/S Moka Pot
Drip: Aeropress
Posted Mon Jan 20, 2014, 9:50pm
Subject: Re: .
 

kolu Said:

I don't actually have means to measure TDS (these instruments are too darn expensive for student on low budget).
So - can simple weighting of dry coffee dose and weighting coffee puck after brewing (and evaporating) the espresso tell me anything useful? Because it looks like this method can't give me the exact extraction yield but some other figure (or ratio) including the undissolved (?) solids.

Posted January 13, 2014 link

The problems with weighing and dehydrating coffee grounds are that (a) you are measuring total solids, and (b) the moisture in the original coffee grounds must be accounted for. When you measure TDS of the coffee beverage the effect of the moisture in the fresh grounds has a relatively small effect on calculation. But when you measure the weight difference of the grounds themselves it is a much larger effect. Basically, every percent of moisture in the fresh coffee grounds will throw off your extraction calcuation by one percent. E.G., if your coffee is 2% moisture and your true extraction is 20% you would measure 22%. So to get reasonable results you have to dehydrate fresh (unbrewed) grounds to determine the moisture content.

An alternative (and still inexpensive) approach is to dehydrate small samples of the coffee liquid. You can buy a milligram resolution pocket scale for about $20-25 and use this to measure samples that are about 1 Tbls in volume to obtain reasonably accurate results.

It's still a pain in the neck to do it when compared to using a high quality refractometer.
And you don't need to do it to make good coffee.
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andys
Senior Member
andys
Joined: 10 May 2003
Posts: 857
Location: NY
Expertise: Just starting

Espresso: Speedster, Londinium 1
Grinder: EK-43,Robur, HG One, M3
Vac Pot: Yama
Drip: various
Roaster: PIDed Popper
Posted Tue Jan 21, 2014, 7:13pm
Subject: Re: .
 

jpender Said:

to get reasonable results you have to dehydrate fresh (unbrewed) grounds to determine the moisture content

Posted January 20, 2014 link

Reasonably fresh-roasted contains more or less equal amounts of moisture and CO2. When you heat the grounds to drive off the moisture, you also drive off the CO2. How does one distinguish between the two?

 
-AndyS
picture page:  http://flickr.com/photos/andy_s/sets/
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kolu
Senior Member
kolu
Joined: 28 May 2013
Posts: 29
Location: Reykjavík, Iceland
Expertise: Pro Barista

Espresso: Grimac La Uno
Grinder: Mahlkönig Guatemala, Porlex
Drip: Kalita Wave, Aeropress
Posted Wed Jan 22, 2014, 10:05pm
Subject: Re: TDS & Distilled Water
 

grind the coffee, weigh it, let it stale (one day?) and then weigh again?
then brew the coffee with fresh grounds and hope the CO2 will be present in equivalent amount?
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jpender
Senior Member
jpender
Joined: 11 Jul 2011
Posts: 708
Location: California
Expertise: I like coffee

Grinder: OE LIDO
Vac Pot: S/S Moka Pot
Drip: Aeropress
Posted Thu Jan 23, 2014, 3:46pm
Subject: Re: .
 

andys Said:

Reasonably fresh-roasted contains more or less equal amounts of moisture and CO2. When you heat the grounds to drive off the moisture, you also drive off the CO2. How does one distinguish between the two?

Posted January 21, 2014 link

I don't think you have to. Whatever volatiles are driven off in the oven during dehydration (edit: or during brewing) of the spent grounds need to also be driven off in a sample of unbrewed grounds in order to get a measure of what was extracted.

As an example, I measured the concentration of a liquid sample from one well-filtered immersion brew to be 1.22%. That translated into a yield of 16.4%, ignoring any volatiles in the initial coffee. If I accounted for the 2.1% "moisture" that I measured by drying fresh unbrewed grounds the yield was 16.8%, a relatively minor adjustment. But the yield I measured by drying the spent grounds was 18.4%, much higher. Adjusting this for the volatiles resulted in a yield of 16.7% which matched the other method within measurement error.

With coffee that had a moisture/CO2/whatever content of nearly 4%, dried spent grounds resulted in unadjusted yields (total solids) as high as 26-28% in my moka pot.
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