Brew Calculator

1. Definitions and mass balance (exact)

water      = dose × ratio                       (g)
beverage   = water − dose × retention           (g)   retention = water held by spent grounds, g per g coffee
dissolved  = EY / 100 × dose                    (g)
TDS        = dissolved / beverage × 100         (%)
measured EY = TDS × beverage / dose             (%)   what you compute from a refractometer reading

These are definitions, not models. Retention per method is a Cup Engineering parameter (pour over 2.1, French press 2.4, AeroPress 2, espresso 1.1, cold brew 2.6, moka 1.6 g/g), chosen from typical practitioner measurements; weigh your beverage if you want the exact number for your brewer.

2. Standards (cited)

The ideal box on the chart is 18–22 % extraction yield by the method's strength window (filter 1.15–1.45 % TDS, espresso 8–12 %), following the SCA Golden Cup standard, itself descended from Lockhart's 1957 brewing control chart. Modern light roasts on good grinders are often brewed happily above 22 %, so the box is a compass, not a fence.

3. The prediction model (Cup Engineering working assumptions)

EY = base(method)
   + 0.9  × (baseGrind − grind)          each step finer adds ~0.9 % EY (more surface area, slower flow)
   + 0.15 × (T − T_default)             per °C, hot methods only
   + 1.4  × log2(time / time_default)   doubling contact time adds ~1.4 % EY (diminishing returns)
   + 0.8  × log2(ratio / ratio_default) more water per gram keeps the concentration gradient steeper
clamped to 8–30 %

The directions of these effects are well established: extraction rises with surface area and contact time and follows diffusion kinetics (multiscale extraction modelling, 2015; espresso modelling, 2020). The coefficients are not fitted to a dataset. They were chosen to reproduce the rough size of effects reported in that literature and in practitioner measurements, and they are deliberately linear so you can see each lever's contribution. Treat the direction and the order of magnitude as reliable and the second decimal as illustrative. Note also that a 2020 UC Davis study found brew temperature, once strength and extraction are held fixed, has little sensory effect, so temperature matters here mainly through the extraction it produces.

Caffeine is estimated as 1.2 % of dose (typical arabica) scaled gently with extraction, since caffeine dissolves early. Per-method bases: Pour Over 20 % at grind 6, 94 °C, 180 s, 1:16.7; French Press 19 % at grind 8, 93 °C, 240 s, 1:15; AeroPress 19.5 % at grind 5, 88 °C, 120 s, 1:13; Espresso 20 % at grind 1.5, 93 °C, 28 s, 1:2; Cold Brew 18 % at grind 9, 20 °C, 16 h, 1:8; Moka Pot 19 % at grind 3, 96 °C, 150 s, 1:7.

4. Multi-stage schedules (Cup Engineering working assumptions)

bloom          +0.8 × (0.3 + 0.7 × e^(−days/8))   even wetting; biggest on fresh coffee
               × 0.5 if bloom water < 1.5× dose; × 0.4 if < 20 s; −0.1 per 15 s beyond 60 s (slurry cools)
               + up to +0.3 for blooms above 2.5× dose; +0.3 swirl / +0.6 stir
no bloom       −0.6 × e^(−days/8) when coffee is ≤ 5 days off roast
pulse pours    +0.30, +0.25, +0.20, +0.15, +0.10 for pours 2…6 (agitation + fresh water)
pre-infusion   +0.4 (< 10 s) or +0.6 (≥ 10 s); pause ≥ 15 s adds +0.5
peak pressure  −0.3 at ≤ 4 bar; −0.2 at ≥ 11 bar; 5–10 bar no change
stirs          +0.3 each, max +0.8; French press break-and-skim +0.2
freshness      −0.4 at ≤ 2 days, −0.2 at 3–4 days

The mechanisms are established: trapped CO₂ repels water and causes channelling, so pre-wetting improves evenness; agitation and fresh water raise extraction; pre-infusion reduces channelling; flow stops responding to pressure above roughly 5 bar. The evidence for the sizes is practitioner-tier (Barista Hustle's bloom and stirring measurements, McKeon Aloe's pre-infusion tests) plus one 2002 pressure study, and there is no peer-reviewed sensory study of pulse pouring. The coefficients are therefore deliberately small and are working assumptions. See the multi-stage brewing article for the sources.

5. Calibrate it to your setup

Brew, measure TDS with a refractometer, enter it below the chart, and log the brew. As logged measurements accumulate, the gap between predicted and measured extraction tells you how your grinder and water differ from the model's assumptions. The plan is to fit these coefficients per grinder once there is enough data (see the analytics page for what has been logged so far).

Sources

1. SCA Coffee Standards: Golden Cup Standard (brewed coffee strength and extraction) — Specialty Coffee Association, Specialty Coffee Association, 2018. Tier 1. Checked 2026-09-05.
2. The Soluble Solids in Beverage Coffee as an Index to Cup Quality — Ernest E. Lockhart, Coffee Brewing Institute (publication), 1957. Tier 2. Checked 2026-09-05.
3. Modelling of coffee extraction during brewing using multiscale methods: An experimentally validated model — Kevin M. Moroney, William T. Lee, Stephen B. G. O'Brien, Freek Suijver, Johan Marra, Chemical Engineering Science, 137, 216-234, 2015-12-01. Tier 1. Checked 2026-09-05.
4. Brew temperature, at fixed brew strength and extraction, has little impact on the sensory profile of drip brew coffee — Mackenzie E. Batali, William D. Ristenpart, Jean-Xavier Guinard, Scientific Reports, 10, 16450, 2020-10-05. Tier 1. Checked 2026-09-05.
5. Systematically Improving Espresso: Insights from Mathematical Modeling and Experiment — Michael I. Cameron, Dechen Morisco, Daniel Hofstetter, et al. (senior author Christopher H. Hendon), Matter, 2(3), 631-648, 2020-01-22. Tier 1. Checked 2026-09-05.
6. Blooming and Clogging (bloom size and agitation experiments) — Barista Hustle, baristahustle.com, 2017. Tier 3. Checked 2026-09-06.
7. Stirring Strikes Back (stirring and extraction experiments) — Barista Hustle, baristahustle.com, 2017. Tier 3. Checked 2026-09-06.
8. Pre-Infusion for Espresso: the calm before the storm — McKeon Aloe R, Towards Data Science (Medium), 2020. Tier 3. Checked 2026-09-06.
9. Influence of Water Pressure on the Final Quality of Arabica Espresso Coffee. Application of Multivariate Analysis — Andueza S, Maeztu L, Dean B, de Peña MP, Bello J, Cid C, Journal of Agricultural and Food Chemistry 50(25):7426–7431, 2002. Tier 1. Checked 2026-09-06.
10. Under pressure: Poroelastic regulation of flow in espresso brewing — Radost Waszkiewicz, Franciszek Myck, Lukasz Bialas, et al. (senior author Maciej Lisicki), Physics of Fluids, 38(6), 063113, 2026-06-01. Tier 1. Checked 2026-09-05.
11. Influence of Flow Rate, Particle Size, and Temperature on Espresso Extraction Kinetics — Schmieder BKL, Pannusch VB, Vannieuwenhuyse L, Briesen H, Minceva M, Foods 12(15):2871, 2023-07-28. Tier 1. Checked 2026-09-06.

Model code: lib/coffee.ts. Information collected 2026-09-05; last reviewed 2026-09-05. Trust tiers per the wiki's sourcing policy.