TDS and Extraction Yield: What Every Home Barista Should Know

Most home brewing advice is qualitative — "brew it a bit stronger," "let it sit a little longer." TDS and Extraction Yield are the two numbers that let you measure a brew instead of just describing it, and they're the backbone of the specialty-coffee approach to dialing in a recipe.

What TDS actually measures

TDS stands for Total Dissolved Solids: the percentage, by weight, of your finished brewed coffee that is dissolved coffee material rather than plain water. A digital refractometer reads this directly — you place a drop of brewed coffee (usually cooled and sometimes filtered) onto the sensor and it reports a percentage, typically somewhere around 1.0% to 1.5% for filter coffee. A TDS of 1.35% means that 1.35% of the liquid's weight is dissolved coffee solids and the rest is water.

TDS on its own tells you how concentrated the cup is, which is related to but not identical to your brew ratio — ratio is what you put in, TDS is what actually came out the other end, after accounting for how much material the water picked up from the grounds.

From TDS to Extraction Yield

Extraction Yield (EY%) answers a different, arguably more useful question: what percentage of the original dry coffee's soluble mass ended up dissolved in your cup? It's calculated with a formula from the SCA's Coffee Brewing Control Chart:

EY% = TDS% × (beverage mass ÷ dose mass)

Take the SCA's own reference example: a 20g dose brewed to 300g of beverage, measuring 1.35% TDS. The brew ratio here is 300 ÷ 20 = 15, so EY% = 1.35 × 15 = 20.25%. That places the brew squarely inside the widely used 18–22% "gold cup" range considered ideal for filter coffee.

Reading the bands

Below about 18% extraction, a brew tends to taste sour, thin, and underdeveloped — the water didn't pull enough soluble material out of the grounds to build a full flavor profile. Above about 22%, a brew tends to taste bitter, harsh, and sometimes hollow — the water pulled out compounds, particularly later in the extraction, that are unpleasant in concentration. The 18–22% band is a reference point built from decades of cupping and consumer-preference testing, not a hard scientific boundary, but it's a genuinely useful starting target.

What actually moves the extraction number

If your EY% comes back low, a few adjustments typically raise it: grind finer (more surface area), use hotter water, extend contact time, or agitate more during brewing. If it comes back high, the opposite adjustments typically lower it: grind coarser, cooler water, or shorter contact time. Ratio itself, notably, doesn't move Extraction Yield anywhere near as much as people expect — you can brew a stronger or weaker cup (different TDS, different ratio) while landing at a similar extraction percentage, because ratio and extraction are controlled by different levers.

A reference, not a rulebook

It's worth being honest about the limits of this framework. The gold-cup chart was built primarily around drip and batch-brew coffee using specific reference equipment and a general consumer-preference panel; it isn't a universal law that every brew, bean, and palate must obey. Two cups with an identical 20% Extraction Yield can taste noticeably different depending on the bean's origin, roast level, freshness, and the water used to brew it. Use the numbers as a diagnostic — "why does this taste sour, and does the math back that impression up?" — rather than a target to chase for its own sake. If a cup tastes good to you outside the reference band, that's not a failure; the band is a starting hypothesis, and your palate is the actual judge.

Getting started without a refractometer

A refractometer is a genuinely useful tool if you brew often enough to want objective feedback, but it's entirely possible to develop a good sense of extraction by taste alone — sour and thin means try finer or hotter; bitter and harsh means try coarser or cooler. If you do want the numbers, the TDS & Extraction Yield Calculator does the arithmetic for you: enter your refractometer reading, dose, and beverage mass, and it reports both the Extraction Yield and where it falls against the reference range.