The Physics of Extraction: What TDS and Extraction Yield Actually Tell You

CoffeeXplore — Tue, 27 Oct 2026 07:21:29 +0000

Taste is a useful guide, but it is also easy to misread. A cup can taste weak because it is under-extracted, because it is diluted, or because both problems are happening at once. Two measurements help separate those explanations: total dissolved solids (TDS) and extraction yield. Used together, they turn dialing in from guesswork into a repeatable test.

TDS is the share of the brewed liquid that is dissolved coffee material, usually expressed as a percentage. A refractometer estimates it by measuring how light bends through a small, cooled sample. Cooling matters, because temperature changes the reading, and a clean prism and a representative sample matter just as much as the instrument itself. TDS tells you how strong the cup is, but not how much of the original coffee was used to make it.

Extraction yield fills that gap. It is the proportion of the dry coffee dose that ends up dissolved in the brew. In simple terms, yield equals TDS multiplied by the brewed beverage mass, divided by the dry dose. For example, a 20-gram dose that produces 300 grams of coffee at 1.35% TDS has extracted about 4.05 grams of material, giving a yield of about 20.3%. That one calculation connects strength, dose, and output in a single check.

The classic brewing-control window is 18–22% extraction yield and 1.15–1.45% TDS. Below that window, coffee often tastes sour, salty, or thin; above it, bitterness and drying astringency are more likely. The window is a starting point, not a guarantee: roast level, coffee origin, and water chemistry all shift what tastes balanced. Still, if two brews taste different, these numbers show whether the difference came from strength, extraction, or both.

Grind size, temperature, and ratio move a brew through the window in different ways. A finer grind increases surface area and usually raises extraction, while a coarser grind lowers it. Hotter water, typically around 92–94°C for drip brewing, extracts more quickly than cooler water. Ratio works in two directions at once: using more water relative to coffee generally raises yield but lowers TDS, while using less water concentrates the cup but may leave more coffee material behind.

For a drip brewer at home, start with a 1:16 ratio—for example, 20 grams of coffee to 320 grams of water—with a medium grind and a flat, even bed. Brew, cool a sample, and measure before changing anything. If yield is low, grind a little finer or raise the temperature slightly. If TDS is high but the cup tastes harsh, try a slightly coarser grind or a little more water. Change one variable at a time and keep notes; otherwise, you will not know which adjustment worked.

For a practical starting point, see CoffeeXplore's ratio explainer. Measurement does not replace tasting, but it gives tasting a direction. When the numbers and your palate agree, you have a recipe worth repeating.

DEV Community: CoffeeXplore

The Physics of Extraction: What TDS and Extraction Yield Actually Tell You