The Brewing Control Chart
Mapping the Perfect Cup
The Brewing Control Chart — developed by the SCA (originally by MIT professor E.E. Lockhart in the 1950s) — is a visual tool that maps the relationship between brew strength (TDS) and extraction yield. It's the scientific foundation of all modern specialty coffee brewing.
Reading the Chart
The chart has two axes: the X-axis shows Extraction Yield (what percentage of the coffee's mass was dissolved, typically 18-22%), and the Y-axis shows Brew Strength/TDS (Total Dissolved Solids in the cup, typically 1.15-1.35% for drip coffee).
The four quadrants:
- Underdeveloped (low extraction, low TDS) — Weak AND sour. Too little coffee, ground too coarse, or brewed too fast. The worst outcome.
- Under-extracted (low extraction, proper TDS) — Sour, sharp, lacking sweetness. Enough coffee used, but not enough dissolved. Grind finer or extend time.
- Ideal Zone (18-22% extraction, 1.15-1.35% TDS) — The golden rectangle. Sweet, balanced, full-flavored. Where specialty coffee aims.
- Over-extracted (high extraction, proper TDS) — Bitter, astringent, harsh. Too much dissolved. Grind coarser or shorten time.
The Brewing Control Chart was revolutionary because it separated two concepts that most people conflate: strength (how much stuff is in the cup) and extraction (how much stuff was pulled from the grounds). You can have strong, under-extracted coffee (like a short espresso) or weak, over-extracted coffee (like drip that brewed too long).
Using the Chart in Practice
To place your brew on the chart, you need two measurements: a refractometer to measure TDS, and a simple formula to calculate extraction yield.
The extraction formula:
- Extraction Yield (%) = (Brewed Coffee Weight × TDS) / Dose × 100
- Example: (250g × 1.35%) / 15g × 100 = 22.5% extraction
- If extraction is too low: grind finer, increase water temp, increase contact time
- If extraction is too high: grind coarser, decrease water temp, decrease contact time
- If strength is too low: increase coffee dose or decrease water volume
- If strength is too high: decrease coffee dose or increase water volume