jpender Senior Member Joined: 11 Jul 2011 Posts: 708 Location: California Expertise: I like coffee
Grinder: OE LIDO Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Fri Jun 22, 2012, 10:22am Subject: Re: Options for Brewing a single Mug that are forgiving of pour technique?
I would agree IF I saw "absorption" vary with extraction in practice. For my BCM-4C, it is consistently ~1.65-1.80, whether I run a short brew with 17% extraction and medium grind, or run an overextracted brew at 7 minutes with fine grind. So, to me it's not a "weak" function of extraction, it is a variable independent of extraction.
You won't easily measure a dependence if the expected variation in extraction (+/-.03) is smaller than the apparently random variation in your absorption constant (+/-.08). You'd have to design an experiment specifically to see it, which makes it a non-issue.
My AP absorption varies more (probably because of the smaller amount of coffee) but still hovers between 1.1 and 1.3 - over a wide range of grind sizes (espresso to french press), contact times (30 seconds to 15 minutes), and brew ratios from 5% to 25%. The other thing I see - overnight steep tends to increase absorption, regardless of grind (to around 1.6-1.7), but again no correlation with strength using same brew ratio (since strength and brew ratio are the primary terms in any calculation of "extraction", regardless of how it's calculated).
I would think that between 5% and 25% brew ratios in an immersion brew you'd get a large enough difference in yield (~0.1) that you might be able to see it -- if you could identify and then control for the other factors that affect absorption. Ironically, extraction might actually affect how much water is absorbed.
I don't know how ExtractMoJo calculates it, but there isn't mystery here. I thought they had a coffee brewing planning model, and the few people that ran some numbers through for me (I don't own the program) seemed to have an absorption of around 2.05 ish. It's calculated pretty simply: A = (Wb - Cp) / C
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