Specialty coffee glossary

#AeroPress

Manual brewing method patented by Alan Adler in 2005. Uses air pressure to push water through ground coffee and a paper filter. Versatile: depending on the parameters, the result can be closer to espresso or to filter coffee.

#Bloom

Initial phase of a pour-over extraction: a small amount of water (about 2× the weight of the coffee) is poured over the grounds, then you wait 30 to 45 seconds. Freshly roasted coffee releases CO₂ (degassing). Skipping the bloom gives an uneven, sour extraction.

#Bottomless

Also called: Naked portafilter

Portafilter without a spout, showing the underside of the coffee puck during extraction. An essential diagnostic tool: you immediately see defects (channeling, poor distribution, uneven tamping). See also our 4 anti-channeling tips guide.

#Channeling

Also called: Tunneling

Espresso extraction defect where water creates a preferential channel through the puck, under-extracting most of the coffee while over-extracting the channel. Visible with a bottomless portafilter as an uneven jet or splattering. Main causes: grind too fine, uneven tamping, irregular distribution, a crack in the puck.

#Cold brew

Cold brewing method: coarsely ground coffee + cold water, steeped for 12 to 24 hours in the fridge. Result is smooth, low in acidity, naturally sweet. Not to be confused with iced coffee (which is hot-brewed coffee cooled down).

#Crema

Golden foam that tops a well-extracted espresso. Made of tiny bubbles of oils, sugars and CO₂ trapped by the pressure. A visual (but not absolute) indicator of coffee freshness and good extraction. A thick, persistent crema usually signals a freshly roasted coffee.

#Degassing

Release of CO₂ by coffee beans after roasting. Very intense during the first 7-10 days, degassing gradually slows down. Coffee that's too fresh (< 5 days after roasting) extracts poorly as espresso. Optimal window: 10-30 days after roasting.

#Distribution

Step before tamping: evenly spreading the grounds in the portafilter to avoid zones of different density. Poor distribution causes channeling. Common tools: WDT (Weiss Distribution Technique), rotary distributors.

#Dripper

Conical or cone-shaped filter holder for the pour-over method: you place a paper filter and the grounds in it, then pour water slowly. Coffee flows through by gravity. Popular models: V60 (Hario), Kalita Wave, Chemex, Origami.

#Espresso

Extraction method under pressure (typically 9 bars) through a finely ground coffee puck. Standard: 18g of coffee, 30-40g output in 25-30 seconds. Produces a concentrated drink topped with crema.

#Extraction

Process by which water dissolves the soluble compounds of ground coffee: acids, sugars, oils, caffeine. Under-extraction gives a sour, flat coffee. Over-extraction gives a bitter, astringent coffee. The goal: balance.

#Filter

Also called: Paper, Metal

A paper filter (V60, AeroPress) retains oils and gives a clean, clear coffee. A metal filter (French press, some moka pots) lets oils through, giving a rounder, fuller-bodied coffee. The choice depends on the flavor profile you want.

#Freshness

Optimal usage window for a coffee: 10 to 45 days after roasting (prefer this date over the packaging date). Too young: hard to extract (CO₂). Too old: flat aromas, oxidation. Storage: airtight bag, stable room temperature, away from light.

#Grind

Particle size after grinding coffee. Must be matched to the brewing method: very fine for espresso (~250 microns), medium for V60 (~600 µm), coarse for French press (~1000 µm). A consistent grind matters more than an absolutely precise one.

#Grinder

The barista's most important tool. Two families: hand grinders (Timemore, 1Zpresso, Comandante) and electric grinders (Eureka, xBloom). A grinder's quality is judged by grind consistency, not just fineness. A good hand grinder at $150 often outperforms a $300 electric grinder.

#Pour-over

Also called: Slow coffee

Family of filter methods where water is manually poured over the grounds sitting in a dripper. Allows full control over flow rate, temperature and water distribution. Flagship methods: V60, Kalita Wave, Origami, Chemex.

#Pressure

Force exerted by the water during extraction. 9 bars is the standard for Italian espresso. Some machines offer pressure profiles (pre-infusion at 2 bars, gradual rise to 9, decline) to better control extraction.

#RDT

Also called: Ross Droplet Technique

Trick from barista David Ross: very lightly moisten the beans before grinding (1-2 drops of water or a spray) to eliminate the static electricity that makes grounds clump. Reduces retention in the grinder and flying particles.

#Tamping

Step of compressing the grounds in the portafilter with a tamper. The goal: create a puck of uniform density to resist extraction pressure. The exact force (20kg, 30kg) matters less than consistency: always apply the same force, perfectly level.

#Roast

Cooking green coffee beans with dry heat. Profiles: light (floral, fruity acidity), medium (balance), dark (bitterness, body, chocolate). Specialty coffee favors light to medium roasts to preserve the flavors of the terroir.

#V60

Also called: Hario V60

The world's most popular dripper, created by Hario. A 60° cone with spiral ribs and a large center hole. Produces a very clean and nuanced extraction. Uses dedicated paper filters.

#WDT

Also called: Weiss Distribution Technique

Distribution technique created by John Weiss: several fine needles are used to stir the grounds in the portafilter before tamping. Breaks up clumps, evens out density and drastically reduces channeling.