How much of your coffee dissolved?

Extraction and strength are different things

Strength, measured as total dissolved solids (TDS), is the share of the cup that is dissolved coffee, about 1.3% for filter coffee. Extraction yield is the share of the dry coffee that ended up in the cup, usually around a fifth. A cup can be strong and under-extracted, or weak and over-extracted, which is why the classic brewing control chart plots one against the other. The calculator is the arithmetic behind that chart, plus the dose that would move you into the target box.

The formula

By conservation of mass, extraction yield (percent) equals TDS (percent) times the weight of the brewed coffee divided by the weight of the dry coffee. Batali, Ristenpart and Guinard (Scientific Reports, 2020) write it as PE = TDS × M_brew ÷ M_grounds. Turned around, TDS = extraction × dose ÷ beverage weight, and the dose for a target strength is TDS × beverage weight ÷ extraction; these two rearrangements are our own algebra. The Golden Cup region as that paper reports it spans a TDS of 1.15% to 1.35% and an extraction of 18% to 22%.

Worked example

You brew 20 g of coffee and collect 320 g of coffee, which reads 1.30% on the refractometer. The yield is 1.30 × 320 ÷ 20 = 20.8%: inside 18 to 22%, and the strength is inside 1.15 to 1.35%, so this cup sits in the Golden Cup box. Now planning: with the same 20 g and 320 g, a yield of 18% would give 1.13% TDS and 22% would give 1.38%. To get 1.25% at 20% extraction in 320 g you need 20 g of coffee. A weaker brew shows the diagnosis: 20 g in 300 g at 1.0% TDS is only 15% extraction, so the first move is a finer grind or a longer brew; the dose alone would not fix it, though at that same yield 25 g would reach 1.25%.

For the ratio itself, use the coffee ratio calculator; this page is for what the brew did with that ratio.

Limits of this method

• The chart is a convention. The same paper that reproduces the Golden Cup box says the classic chart is problematic from a modern sensory point of view, because it mixes hedonic words (“ideal”) with measurements. Plenty of good cups sit outside it.
• Measurement error. The study read a cooled drop with a digital refractometer that it had checked against oven-dried samples. A warm, unfiltered or smudged sample reads wrong, and a small error in TDS moves the yield by the same relative amount.
• Brewed weight, not water weight. Using the water you poured overstates the yield, because the spent grounds keep part of it.
• Filter coffee only. The ranges come from drip brewing research. Espresso is brewed to very different strengths, so do not judge it by this box.
• Temperature is a weak lever at fixed extraction. In that study, 87 to 93 °C made no appreciable sensory difference once TDS and extraction were held constant; grind and time are the practical levers.

How do I calculate coffee extraction yield?

Multiply the TDS of the brewed coffee by its weight and divide by the dry coffee you used: extraction yield = TDS × beverage weight ÷ dose. Batali, Ristenpart and Guinard print it as PE = TDS × M_brew ÷ M_grounds. With 20 g of coffee making 320 g of brew at 1.30% TDS, the yield is 1.30 × 320 ÷ 20 = 20.8%. Weigh the brewed coffee, not the water you poured, because the grounds keep part of the water.

What is the Golden Cup range for extraction and strength?

The central “ideal” region of the classic brewing control chart is a TDS of 1.15% to 1.35% and an extraction of 18% to 22%, which the Specialty Coffee Association calls its Golden Cup Standard, as reported in a 2020 Scientific Reports study. The chart then labels cups below 18% as underdeveloped, above 22% as bitter, and by strength as weak or strong.

My coffee tastes sour or weak. What should I change?

First find out whether the problem is extraction or strength, because they have different fixes. If the extraction yield is under 18%, not enough has dissolved: grind finer or brew longer; in the study, the researchers reached each extraction target by changing the grind size and brew time. If extraction is fine but TDS is under 1.15%, use more coffee for the same water, since at a fixed extraction the strength is proportional to the dose. Example: 20 g in 300 g at 1.0% TDS is 15% extraction; the same extraction at 1.25% needs 25 g.

Does water temperature change extraction?

Less than most people think once strength and extraction are held fixed. In the Scientific Reports study, drip coffee brewed at 87, 90 and 93 °C was tasted by a trained panel, and the sensory differences came from TDS and extraction, not from the temperature; the authors adjusted grind and brew time to keep the extraction the same. Measure the result rather than assuming.

How do I measure TDS at home?

With a refractometer. The study cooled a drop of the brewed coffee to room temperature in an ice bath before reading it, with a digital refractometer that was checked against oven-dried samples. Keep grounds off the instrument and read the same sample more than once.

How is this different from a coffee ratio calculator?

A ratio calculator, like our coffee ratio calculator, tells you how much coffee and water to use. This one starts from what the brew actually did: how much of the coffee dissolved (extraction) and how concentrated the cup is (strength). Two brews with the same ratio can have different extraction if the grind or the time differs, and this calculator shows it.

Sources: M. E. Batali, W. D. Ristenpart and J.-X. Guinard, “Brew temperature, at fixed brew strength and extraction, has little impact on the sensory profile of drip brew coffee”, Scientific Reports 10, 16450 (2020), with its 2021 correction; the paper cites E. E. Lockhart (1957), T. R. Lingle, The Coffee Brewing Handbook, and the Specialty Coffee Association Coffee Standards (2018), which we did not open ourselves. Related: coffee ratio calculator, caffeine in body calculator and cooking measurement converter.