Posted Tue Jan 29, 2013, 12:07pm Subject: Re: Temperature and Immersion/Steep Brewing
some of the other calcs you see are getting into mouse nuts, too.
For example, if you have 1% CO2 in your sort-of fresh brew coffee, then what is your denominator at the end of brewing for calculating extraction yield percent? And how do you know if it's 0%, 1% or 4% of CO2 in your brew coffee?
12g of brew coffee might actually contain:
0.25g CO2 (which essentially dissipates after brewing/bloom) 0.25g H2O (remember, coffee isn't perfectly dry)
so is your denominator for extraction percent 12g, 11.75g or 11.5g?
Is your brew water 185g, or does it include the 0.25g of H2O that was in the water, and is it actually 185.25g?
If we're fussing about all of this, why do we neglect the extra ~0.25-0.50g of evaporation and loss that inevitably happens during the brewing process? W+C doesn't equal G+P, and not all of that loss is CO2. Even with a well-measured AeroPress brew, the loss is usually in the neighborhood of 1g or so during the brew process. Don't forget there's also undissolved solids that make it to the cup - we don't measure those directly, either, but they're there, and are part of the mass of the produced coffee.
Remember - we never measure "extraction yield" directly - we can only measure the concentration of the solution, and then mathematically infer the extraction based on some assumptions.
I know I don't have a device that tells me how many grams of UNdissolved solids (fines, micromud, sludge) make it to the cup. Nor am I aware of a device that can tell me accurately that I have 1.24% CO2 and 2.18% H2O in my brew coffee.
Bottom line for these calcs, think of it as the following:
All of the water in immersion brewing is part of a solution of coffee at the same strength throughout the liquid. Think of the "cup" of produced coffee as a sample of the solution, for which you can measure the strength.
If you use 185g of water to dissolve some coffee, and end up with 155g sample at 1.27% strength, then you know that the sample consists of 1.97g of total dissolved solids, and 153.03g of water.
If there are no losses, then the rest of the water (185-153.03 = 31.97g) is stuck in the grounds, in solution at the same strength as in the cup. The remaining water in the grounds is part of a solution that is 1.27% strength, or stated differently the total dissolved solid mass is 0.0127 fraction of the solution, and the water is (1 - 0.0127 = .9873) fraction of the solution.
That's where the (1-S) comes from. Since Strength is the total dissolved solids / SOLUTION Mass (not just the water).
A solution of 0.411g solute dissolved by 31.97g of water (total mass of the solution is 32.381g) is 1.27% strength.
You have 0.411g solute in the grounds that never made it to the cup, and 1.97g of solute in the cup - so the process actually dissolved 2.381g of coffee solute - divide that by 12g of coffee, and you get 19.8%.
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squaremile Senior Member Joined: 6 Jan 2011 Posts: 39 Location: Portlandia Expertise: Just starting
Posted Tue Jan 29, 2013, 2:39pm Subject: Re: Temperature and Immersion/Steep Brewing
OK very good stuff. I see how this all fits together now. And the CO2 and H2O in the coffee, plus the evaporation... I guess that's why I aim for the middle (20% extraction) and pray that it tastes good :)
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