Module 3
Extraction physics & water
EY % = (brew weight × TDS %) / dose. Strength is how dark the cup is; extraction is how much of the dry coffee you dissolved. They are not the same axis.
EY (%) = (yield × TDS %) / dose
EY
21.67%
Ratio
1:16.7
TDS
1.30%
Gold Cup zone. Hold the grind and ratio; change one variable only if you chase a different flavor.
SCA brewing control chart
Target 18–22% EY · 1.15–1.45% TDS (SCA Gold Cup).
SCA water standard
Hardness vs buffer
Ca²⁺ and Mg²⁺ extract flavor; HCO₃⁻ buffers acids. Hendon: magnesium is the more efficient extractor, bicarbonate is the mute button.
TDS 75–250 mg/L · pH 6.5–7.5 · chlorine 0. Recipe water, not tasting water.
The other levers
Grind distribution
Fines extract fast and clog; boulders stay sour. The mean grind size is less important than the spread. Flat burrs trend unimodal (clarity); conicals, bimodal (body). Gagné: bypass and fines are the hidden axes of filter coffee.
Temperature
SCA: 92–96 °C at the bed for filter. Lower temps under-extract acids’ companions (sugars, melanoidins); higher temps pull more bitter phenolics. Dark roasts often prefer the bottom of the range.
Contact & agitation
Time is a proxy for mass transfer. Swirls and pour-height add turbulence, thinning the boundary layer. Channeling — preferential paths in espresso or a V60 crater — is uneven contact, not a vibe.