Reference
Coffee glossary
Plain-English definitions of the coffee terms used across our buying guides.
- Extraction
- The process of dissolving flavor compounds from ground coffee into water. Under-extracted coffee tastes sour and thin; over-extracted coffee tastes bitter and dry. Grind size, water temperature, and brew time control it.
- Grind size
- How coarsely or finely coffee beans are ground. Espresso needs a fine grind, pour-over a medium grind, and French press a coarse grind. Consistency matters more than the exact setting.
- Crema
- The golden-brown foam that forms on top of a well-pulled espresso shot. It comes from CO2 and oils emulsifying under pressure, and fresh beans produce more of it.
- Bloom
- The initial pour in pour-over brewing where hot water releases trapped CO2 from fresh coffee, causing the grounds to swell. A 30–45 second bloom leads to more even extraction.
- Burr grinder
- A grinder that crushes beans between two burrs for a uniform particle size. Conical and flat burrs both beat blade grinders, which chop unevenly and hurt flavor clarity.
- Pre-infusion
- A low-pressure wetting phase at the start of an espresso shot, before full 9-bar pressure is applied. It reduces channeling and improves shot consistency.
- Channeling
- When water finds the path of least resistance through a coffee puck, over-extracting some grounds and under-extracting others. Even distribution and tamping prevent it.
- TDS (total dissolved solids)
- A measurement of how much coffee material is dissolved in the brewed cup, usually read with a refractometer. It quantifies brew strength, not flavor quality.
- Single origin
- Coffee from one farm, region, or cooperative, as opposed to a blend. It highlights distinctive flavors of a place but varies more from harvest to harvest.
- Roast level
- How dark the beans were roasted: light roasts preserve origin character and acidity, dark roasts taste bolder and more caramelized. Espresso blends are often medium-dark.
- Descaling
- Removing mineral buildup from a coffee machine's boiler and water paths with a descaling solution. Hard water areas need it every 1–3 months to protect heating elements.
- Backflushing
- Cleaning an espresso machine's group head by running water with a blind filter basket and detergent. It removes rancid coffee oils that turn shots bitter.