BREW LAB

Extraction yield tells you what share of the coffee grounds has dissolved into the water. It follows from three numbers: the concentration of the finished beverage, its mass, and the dose of coffee you started with. That concentration is called TDS, total dissolved solids, and it is read off a refractometer.

The Brew Lab runs this equation in both directions. Without a refractometer it estimates TDS from your recipe and what you know about the bean. The moment you enter a measured value it reverses the calculation and replaces the estimate throughout the whole result.

Extraction and strength get lumped together in everyday talk, yet they hang off different levers. Extraction describes how much came out of the coffee, and it decides between sour and bitter. Strength describes how much of that sits in a single sip, and it decides between thin and heavy.

For filter coffee the grind moves extraction above all, the ratio moves strength. For espresso the shot time takes the role of the grind and the yield takes the role of the ratio. Change both axes in the same brew and you will not know afterwards which lever did the work. That is why the correction panel only ever names one change.

The chart plots extraction along the horizontal axis and TDS along the vertical one. The solid rectangle is the Golden Cup zone of the Specialty Coffee Association: 18 to 22 % extraction at 1.15 to 1.35 % TDS. There is no single correct TDS value here: North America traditionally sets 1.15 to 1.35 %, Europe more often 1.20 to 1.45 %, Nordic roasters often 1.30 to 1.50 %. The dashed strip above the solid rectangle covers that range up to 1.42 % and marks where many modern filter recipes deliberately sit.

The lines around the corridor continue across the whole field and divide it into nine fields. They tell you what a deviation tastes like: left turns sour, right bitter, up heavy, down thin. You correct sideways with the grind and vertically with the ratio.

The diagonals are brew ratios. Move along a diagonal and extraction shifts while the ratio of coffee to water stays put. Espresso has no official Golden Cup equivalent. The corridor of 8 to 12 % TDS is industry practice, not a standard.

Grinders do not speak the same language. The Brew Lab therefore states the recommended grind in micrometres and converts it into your grinder's scale as well: Comandante C40 with and without Red Clix, C60 and X25, Mahlkönig EK43 and EK43 S, Kinu M47, 1Zpresso JX-Pro, Timemore C2 and C3, Kingrinder K6, Baratza Encore and Fellow Ode Gen 2.

Those are comparison figures, not a calibration. Every burr set differs a little and changes as it breaks in and wears. Take the number as a starting point and note down your own offset. From then on it holds for every further recommendation.

The Brew Lab is a model, not a measuring instrument. It gives a forecast from your recipe and what you know about the bean. How far one particular lot departs from that is something only a measurement can tell you.

The axes acidity, sweetness, bitterness, body and aftertaste are known to respond to extraction and TDS. Clarity and astringency, by contrast, are practitioners' terms rather than official scoring attributes. The calculation runs on our server; a brew is only stored once you save it to your account.