Chang94598 Senior Member Joined: 24 Oct 2007 Posts: 213 Location: SF Bay Area
Posted Mon May 14, 2012, 10:54am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
My understanding for the brew formula is:
Strength= (Coffee*Extraction%) / (Total Water - Total Water * Absorption)
Dr Lockhart from the Coffee Brewing Institute used 2.086 ml of water absorbed per gram of dry coffee. In my experience of brewing single cup drip and Abid, the absorption rate is about 2.25 g (not ml) per gram of dry coffee.
The ground coffee water absorption is time and water quality dependent. Coffee will retain more softer or distilled water, and vice versa. In drip, it also varies if the paper is pre-wet or not (duh, obviously).
The decision to use volume vs weight is size. I assume in commercial settings, where large amount of coffee is needed, volume is easier. In home setting, weight is convenient. It is only a matter of molality vs molarity, just like in a chemistry lab.
jpender Senior Member Joined: 11 Jul 2011 Posts: 742 Location: California Expertise: I like coffee
Grinder: OE LIDO Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Mon May 14, 2012, 12:35pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
The drip pot: 40g coffee, 415g brew water (added 15 for evaporation), 328.1g produced at 2.75%. Yield based extraction back calculates to 22.5%, and is in line with how it tastes (over extracted). The spent coffee weighed 112.3g (so the absorption was around 1.808).
I think the most likely explanation is that the liquid retained in the wash through method is much weaker in dissolved solids than that of the immersion method.
Suppose that the retained liquid is of strength 0% for the filter brew and is equal to the strength in the cup of the Aeropress brew. If you could somehow wash out those retained dissolved solids the extraction yields of the two brews would be nearly identical.
It's inconsistent in the same way that 100+1=100 is. It's an approximation, albeit a pretty good one for normal conditions. Outside that range it diverges somewhat more. Isn't one of your goals to improve the predictive power of these formulas/charts? If it were me I would make approximations after I got there, not before.
But this isn't the interesting part of your question.
<sigh> How are you going to explain that to Lord Kelvin?
Meanwhile, I'm expecting that you're going to put together some kind of Unified Field Theory of Coffee Extraction. On one end of the extraction spectrum you'll have espresso and pourover brews, where the liquid trapped in the grounds at the end is weak enough (the Weak Force) to be ignored. On the other end you'll have cupping, Eva Solo and perhaps French Press, where the liquid trapped in the grounds is approximately the same strength (the Strong Force) as the beverage, and will be counted in the extraction. Other methods, such as vac pot and Aeropress will fall in specific intermediate areas. They each will have their own Cosmic Coffee Constant that will offset their measurements relative to the others. In the end, 19% extraction will taste about the best for all methods.
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