Two different dials: strength and extraction
Extraction is how much of the coffee's soluble material ended up in the water, as a share of the dry grounds. Too little and the cup tends to taste sour and hollow; too much and it tends to turn bitter and drying. The brewing control chart grew out of E. E. Lockhart's work in the 1950s.
Strength is the concentration of dissolved coffee in the drink, measured as total dissolved solids (TDS), and it is set mostly by the ratio of coffee to water. This map uses the SCA's March 2019 chart as its reference: 1.15–1.45% TDS and 18–22% extraction. Earlier Golden Cup guidance used 1.15–1.35% TDS. These ranges help compare brews; your preferred strength can fall outside them.
Later UC Davis research found that different groups of coffee drinkers preferred different brewing conditions. Taste your cup before deciding what to change: a higher strength does not, by itself, mean over-extraction.
Because they're separate, a cup can be strong and sour, or weak and bitter. That's why the map has two axes and nine zones.
The nine zones
- Under-extracted and weak tends to taste sour and watery. Move: grind finer; use more coffee.
- Under-extracted tends to taste sour, body about right. Move: grind finer; hotter water; longer contact.
- Under-extracted and strong tends to taste sour but intense; often channeling. Move: even out the bed; grind a touch coarser to stop clogging; then fine-tune.
- Well extracted, too dilute tends to taste pleasant but thin. Move: use more coffee (stronger ratio).
- Sweet spot tends to taste sweet, balanced, clear. Move: keep it: write down this recipe.
- Well extracted, too strong tends to taste heavy and intense. Move: use more water (lighter ratio).
- Over-extracted and weak tends to taste bitter and thin, like stewed diner coffee. Move: grind coarser; use more coffee.
- Over-extracted tends to taste bitter, drying finish. Move: grind coarser; cooler water; shorter contact.
- Over-extracted and strong tends to taste harsh and heavy. Move: grind coarser; use more water.
Estimated extraction by brew method
These bands are our estimates, the ones the Brew Guide uses for its strength figures, not published measurements; the map is centered on the sweet spot rather than any one method.
- V60: about 19–21%
- Chemex: about 18–20%
- Kalita Wave: about 19–21%
- French press: about 20–22%
- AeroPress: about 19–22%
- Cold brew: about 15–20%
- Drip machine: about 18–22%
- Espresso: about 18–22%
- Moka pot: about 15–19%
How to calculate extraction yield
With a refractometer reading, extraction is simple arithmetic: extraction yield (%) = drink weight × TDS (%) ÷ coffee dose. An 18 g espresso dose that gives a 36 g shot at 10% TDS has extracted 3.6 g of coffee, which is 20%. A 20 g pour-over that gives 300 g of coffee at 1.3% TDS has extracted 3.9 g, or 19.5%.
For immersion brews (French press, AeroPress, cold brew), use all the water you added instead of the drink weight, because the liquid left in the grounds is as strong as your cup. That simple version reads slightly low. Take an immersion reading before you dilute: the grounds hold back some of the dissolved coffee, so the formula can't use a diluted cup. For pour-over and espresso, if you dilute afterwards (an americano, bypass water), take the weight and the reading at the same point: the dissolved coffee doesn't change when you add water.
A refractometer is the only way to measure TDS at home. Without one, taste is a good guide, and the map is a way to reason about it: a hypothesis, not a reading.
Sources
- Specialty Coffee Association, Coffee Brewing Control Chart, revised March 2019 (Version 3) (2019): reference region: extraction 18–22%, strength 1.15–1.45% TDS.
- Specialty Coffee Association, Coffee Standards, revised 2018 (2018): §5.1 Golden Cup: extraction 18–22%, strength 1.15–1.35% TDS.
- Cotter, Batali, Ristenpart and Guinard, Consumer preferences for black coffee are spread over a wide range of brew strengths and extraction yields (Journal of Food Science 86: 194–205) (2021).
- Jonathan Gagné, The Physics of Filter Coffee (2021): V60 method; extraction and strength.
- Scott Rao, The Professional Barista's Handbook; Espresso Extraction: espresso dose, ratio, time and temperature; batch brewing.
- Jessica Easto, Craft Coffee: A Manual (2017): brewing method chapters (V60, Chemex, Kalita Wave, French press, AeroPress, cold brew).
- JayArr Coffee, Coffee Knowledge Synthesis (seventeen sources): §6 recipes, §17 method comparisons, §19 key numbers, §23 brewer base parameters.