Reference · glossary

Coffee brewing glossary

The words brewers use for what happens in the filter — bloom, slurry, bypass, drawdown — and the measurements behind a recipe: brew ratio, TDS, extraction yield. Each definition follows a standard, a study or a named source, and links to the lab page that goes deeper.

Updated 2026-10-26 · sources listed at the end

A

Agitation

Any stirring, swirling or turbulent pouring that moves the grounds in the slurry. Barista Hustle notes that agitation such as stirring during the bloom "is known to cause fines to lodge themselves in the filter paper", which can slow the drawdown.

B

Bed (coffee bed)

The layer of grounds that water flows through in a dripper or espresso basket. Flow through it is not uniform: in a model by Lee, Smith and Arshad, "regions with higher porosity will see more flow and thus more extraction" — one way uneven extraction arises (see channeling).

Bloom

The small first pour that wets the grounds, after which fresh coffee bubbles as carbon dioxide escapes. The SCA's Coffee Decoded column links stronger blooms in filter brewing to CO₂ and says degassing is rapid for the first 20 days after roasting. In a Barista Hustle V60 test (15 g coffee, 250 g water), bigger blooms slowed the drawdown and raised extraction, though the team could not separate the bloom itself from the longer contact time. More: coffee bloom explained.

Brew ratio

"The ratio of coffee to water when preparing a brew" (SCA Standard 310-2021). The standard's reference ratio is 55 g of coffee per 1.000 kg of water; the SCA's brewing best practices give 55 g/L ± 10%, about 1:18 written as grams of water per gram of coffee (our arithmetic). Calculator and ratios by method: coffee-to-water ratio.

Brewing control chart

A chart with TDS on the vertical axis, percent extraction on the horizontal axis and brew ratios as diagonal lines. It grew out of work by biochemist Ernest Earl Lockhart, whose 1957 paper was titled "The Soluble Solids in Beverage Coffee as an Index to Cup Quality"; its central box is labelled "Ideal – Optimal Balance". UC Davis researchers have since tested and redrawn it: brewing control chart explained.

Bypass

Water "that finds its way into the final brew without having passed through a bed of ground coffee" (Daily Coffee News). Accidental bypass is a fault: less water reaches the bottom of the bed, which stays less extracted. Intentional bypass, described as a potential time saver in commercial settings, brews with more coffee and/or less water into a concentrated brew that is then diluted to strength. "Zero-bypass" brewers are built to remove the accidental kind. Diluting a concentrate after brewing follows the same arithmetic as the AeroPress concentrate recipes.

C

Channeling

Water finding preferred paths through the coffee instead of flowing evenly. In espresso, a 2026 AIP Publishing release on University of Warsaw research describes channeling as an issue that arises as hot water passes through the pressed puck: water "follows the path of least resistance", so extraction is uneven. See bed and the espresso ratio guide.

Contact time

How long water and grounds stay together. The SCA's best practices pair it with grind: 1–4 minutes fine, 4–6 drip, 6–8 coarse. SCA Standard 310-2021 measures brew time as "operation time", from the moment the user starts the cycle. Grind settings by method: grind size chart.

D

Degassing

Roasted coffee slowly releasing the CO₂ formed in roasting. According to the SCA, whole beans degas quickly for about 20 days and then much more slowly, while "the CO₂ that is lost over weeks in whole bean coffee is lost in minutes after coffee is ground"; the column suggests ground coffee may stay fresh for about an hour. The gas left in the grounds is what makes a bloom. More: coffee freshness.

Drawdown

The phase after the last pour when the remaining water drains through the bed; brewers time it as the drawdown time. Barista Hustle divides the water of the main pour by the drawdown time to get an approximate average flow rate, and attributed slower drawdowns after bigger blooms to fines blocking pores in the filter paper. Total brew times for specific drippers: V60 guide and pour-over.

E

Extraction yield EY · PE

"The percentage in mass of the fresh coffee grounds which is extracted into the brew" (SCA Standard 310-2021, which also calls it brew yield or percent extraction). Wikipedia gives 18–22% as desirable for most traditional coffee beverages. It is calculated from TDS, beverage weight and dose: extraction yield calculator. Not the same as strength.

F

Fines

The smallest particles a grinder makes. Counter Culture Coffee describes them as "less than 200 microns", produced every time coffee fractures; Smrke, Eiermann and Yeretzian (2024) use particles below 100 µm, so definitions differ. In their espresso study a larger share of fines decreased bed permeability, reduced flow and lengthened extraction. Wikipedia notes fines add suspended solids that change mouthfeel, "particularly in French press brewing". More: coffee grinders explained.

Fines migration

The idea that fines move down through the bed and collect against the filter, where they can clog it and slow the flow. Evidence is mixed: Barista Hustle assumed fines blocking filter pores explained its slower V60 drawdowns, but in a 2019 Barista Hustle espresso test, in which ground coffee was tapped 100 times before brewing, the team "didn't find much evidence for the idea that fines migrate in dry coffee".

G

Golden Cup Standard

The SCA's brewing benchmark: a coffee-to-water ratio of 55 g/L ± 10% and water at 200 °F ± 5° at the point of contact with the coffee. The SCA cupping ratio of 8.25 g per 150 ml is described as the mid-point of the Golden Cup recipes. Temperature detail: water temperature.

I

Immersion

Brewing with all the grounds steeping in all the water, as in a French press or a vacuum (siphon) brewer; in these methods, according to Wikipedia, "extraction takes place slowly". Compare percolation. Guide: French press.

O

Over-extraction

Taking too much out of the grounds. Wikipedia: yields over 22% "are considered over-extracted and are often associated with a predominant bitterness". Opposite: under-extraction.

P

Particle size distribution

"The specific combination of these different particle sizes" in a batch of ground coffee (Counter Culture Coffee). Grinding fractures coffee into many sizes at once; the spread, including the share of fines, affects flow and extraction (Smrke et al. 2024).

Percolation

Brewing by passing water through a column of grounds, as in pour-over and espresso (Wikipedia). Not the same as the stovetop percolator, which Wikipedia notes is prone to over-extraction because the coffee passes through the grounds several times.

Pulse pouring

Adding the brew water in several timed portions instead of one. In the 4:6 method of Tetsu Kasuya, 2016 World Brewers Cup champion, the first 40% of the water sets acidity and sweetness and the remaining 60%, split into equal pours, sets strength (HARIO Europe). Pour timings for any dose: pour schedule generator.

R

Refractometer

"A refractometer especially designed to estimate the total dissolved solids (TDS) in the coffee brew" (SCA Standard 310-2021). How readings work and what limits their accuracy: coffee TDS and refractometers.

S

Slurry

"The dynamic mix of coffee grounds and water produced inside the filter during brewing" (SCA Standard 310-2021). The standard's temperature test is measured in the slurry: 90–96 °C once a third of the water has been sprayed.

Strength

"The amount of total dissolved solids (TDS) in the brew, expressed in percentage or in parts per million" (SCA Standard 310-2021). SCA-certified home brewers must reach 1.15–1.55% at the standard 55 g/kg ratio. Wikipedia puts most beverages at 1.15–1.35% and the Nordic ideal at 1.30–1.50%.

T

TDS total dissolved solids

The measure of how much of the coffee grounds dissolved into the liquid (Frost and colleagues, SCA 25); in brewing, TDS of the brew is its strength. Measured with a refractometer. The same abbreviation is also used for brewing water: water chemistry.

U

Under-extraction

Taking too little out of the grounds, "often associated with a predominantly sour taste" (Wikipedia): acids dissolve early, while the sugars and bitter compounds that balance them dissolve later. Opposite: over-extraction.

The numbers at a glance

Definitions vary between sources — fines are the clearest example. Where a term here has an SCA definition, that is the one quoted; everything else names its source in the entry.