Coffee glossary

Definitions

Brew ratio

Brew ratio compares dry coffee to liquid. For pour-over it is usually coffee : water (1:15–1:17). For espresso it is dose : beverage yield (1:2 is a typical starting double). Changing ratio changes strength more immediately than changing grind. Weigh both sides; volume of a crema-topped shot is a poor proxy for grams.

Extraction yield

Extraction yield is the share of the dry dose that dissolved into the cup. EY% = TDS% × yield / dose. Under-extracted shots taste sour and thin; over-extracted shots go dry and bitter. SCA’s 18–22% window is a starting band, not a law — roast, grind and water move it. You need a refractometer for TDS; guessing EY from taste alone is folklore.

TDS

TDS (total dissolved solids) is how concentrated the drink is, usually read with a coffee refractometer. Filter coffee often lands near 1.2–1.5%; espresso 8–12%. TDS is strength. Extraction yield needs TDS and the brew ratio. Bypass water lowers TDS without changing how far the grounds were extracted.

Grind size

Grind size is the particle-size distribution leaving the burrs. Converters estimate mean size as clicks × microns per click from burr lock or a published zero. That is a relative map, not a laser diffraction lab. Finer grind extracts faster and chokes espresso; coarser grind under-extracts and races through a puck. Match size to brew method, then taste — clicks are not universal between brands.

GH and KH

GH (general hardness) is calcium plus magnesium. KH (carbonate hardness) is alkalinity, mostly bicarbonate. Coffee recipes target roughly 50–80 ppm GH and 40 ppm KH as CaCO₃, in the SCA ballpark. High KH mutes acidity; very soft water can taste sharp and scale less. German degrees: °dH ≈ ppm / 17.8. Test strips and lab reports disagree — treat recipes as starting water, then taste.

First crack

First crack is the popcorn-like sound when cells rupture and steam leaves the bean. Many roast profiles start “development” at the onset of first crack. Hitting it too hot or too fast bakes the roast; dragging it too long flattens acidity. Second crack is a later, oilier stage. Listen, log bean temperature, and do not treat a phone recording as a lab sensor.

Development time ratio

Development time ratio (DTR) is (time after first crack) / total roast time. A common starting band is 20–25%. Shorter DTR keeps more acidity and can taste grassy if underdeveloped; longer DTR pushes sweetness then roastiness. DTR is a clock ratio, not a colour meter — two roasts with the same DTR can still miss if rate of rise collapsed after crack.

Degassing

Degassing is CO₂ leaving the bean after roast. Too soon and espresso pucks bloom, channel and spray; too late and aromatics fade. Light roasts often peak later (a week or more); dark roasts can be ready in a few days. Storage, roast level and dose all move the window. A rest timer is a calendar estimate, not a gas chromatograph.

Caffeine

Caffeine is an alkaloid extracted with water. Arabica beans hold roughly 1.2% by dry mass; robusta about twice that. Brew method and contact time change how much ends up in the cup. Population guidelines (FDA ~400 mg/day, EFSA 3 mg/kg, pregnancy often 200 mg) are not medical advice. These calculators estimate milligrams from dose and a simple extraction factor — they do not assay your beans.

Bloom

Bloom is a small first dose of water (often ~2–3× coffee mass) left for 30–45 seconds on a pour-over or batch brew. Gas leaves, the bed settles, and later pulses wet more evenly. Fresh light roasts bloom harder. Skip it on fully degassed coffee if you want; it is a wetting step, not magic. Espresso “blooms” as crema and gas in the puck — that is a related CO₂ story, different mechanics.

Channeling

Channeling happens when water finds a low-resistance path in the puck. You get blond jets, fast shots, sour-bitter split cups and a messy basket. Distribution (WDT), even tamps, a level portafilter and a grind that actually resists 9 bar all help. Calculators that spit out a yield cannot see a channel. If the shot ran two seconds fast, fix prep before you chase the ratio.

Roast level

Roast level is how far the bean was taken past drying and Maillard into development. Weight loss of ~12–14% is often city / light-medium; ~16–18% darker. Names (City, Vienna, French) are trade slang. Colour meters and Agtron exist; a kitchen scale is a crude proxy. Darker roasts degas faster, taste more bitter-sweet, and hide origin acidity.