Coffee and espresso glossary
Plain definitions for the words that get used on coffee bars and in gear reviews without ever being explained. Each entry says what the term means and, where it matters, why it matters to the cup. Where we have a full guide on a term, it is linked.
Crema
The tan foam on top of an espresso shot, formed when carbon dioxide trapped in the beans is released under pressure. Thick crema means fresh beans and a decent shot, but it is not proof of a good one: pressurised baskets fake it. Read more.
Channeling
When water finds a low-resistance path through the coffee puck instead of soaking it evenly. The shot runs fast and tastes thin and sour because most of the grounds were barely touched. Read more.
Tamping
Compressing the grounds in the portafilter into a level, even puck. Level matters more than force: a tilted puck channels no matter how hard you press. Read more.
Portafilter
The handled basket holder that locks into the machine. Sizes differ by machine, commonly 51mm, 54mm and 58mm, and baskets and tools are not interchangeable across sizes.
Naked portafilter
A portafilter with the bottom removed so you can watch the shot leave the basket. It is a diagnostic tool: channeling becomes obvious the moment it happens.
Dose
The dry weight of ground coffee going into the basket, in grams. A common double is 18g.
Yield
The liquid weight coming out of the basket, in grams. Weighing yield rather than eyeballing volume is the single biggest accuracy upgrade for espresso.
Brew ratio
Dose to yield. Espresso commonly runs about 1:2, so 18g in and 36g out. Pour over commonly runs about 1:16. Read more.
Extraction
How much soluble material the water pulls out of the grounds. Too little tastes sour and thin, too much tastes bitter and drying.
Under-extraction
A shot or brew that stopped too early or ran too fast. Sour, sharp, and often thin.
Over-extraction
A shot or brew that ran too long or too fine. Bitter, dry, and hollow in the finish.
Dialing in
Adjusting grind, dose and time until a coffee tastes right on your machine. Change one variable at a time or you learn nothing.
Grind size
How coarse or fine the coffee is ground. It is the main lever for shot speed: finer slows the flow, coarser speeds it up. Read more.
Burr grinder
A grinder that crushes beans between two burrs, producing a consistent particle size. Blade grinders chop unevenly, which makes espresso unpredictable.
Distribution
Spreading the grounds evenly in the basket before tamping, so water meets equal resistance everywhere. Read more.
WDT
Weiss Distribution Technique: stirring the dry grounds with fine needles to break up clumps before tamping. Cheap, and it reduces channeling more than most gear upgrades.
Preinfusion
Wetting the puck at low pressure before full pressure begins, so the coffee swells evenly and resists channeling.
Ristretto
A shorter espresso, less water through the same dose. Denser and sweeter, with less of the bitter late extraction.
Lungo
A longer espresso, more water through the same dose. Lighter in body and more bitter as extraction continues.
Doppio
A double espresso, two shots pulled into one cup from a double basket. Read more.
Macchiato
Espresso marked with a small amount of milk foam. The cafe version and the chain version are very different drinks.
Cortado
Espresso cut with an equal amount of warm milk, usually served in a small glass.
Flat white
Espresso with steamed milk and a thin layer of microfoam, smaller and stronger than a latte. Read more.
Americano
Espresso diluted with hot water. Adding espresso to water rather than water to espresso preserves more crema.
Breve
Espresso with steamed half and half instead of milk. Richer and heavier. Read more.
Affogato
A scoop of ice cream with a shot poured over it. Dessert, not a coffee order.
Cold brew
Coffee steeped in cold or room temperature water for many hours, then filtered. Lower in perceived acidity than hot brewed coffee.
Nitro cold brew
Cold brew infused with nitrogen, which gives it a cascading pour and a softer, creamier texture without any dairy.
Pour over
Brewing by pouring hot water through a bed of coffee in a filter cone. Slow, controllable, and unforgiving of a bad grinder. Read more.
Bloom
The first pour in a pour over, wetting the grounds and letting trapped carbon dioxide escape before the main pour begins.
Gooseneck kettle
A kettle with a narrow curved spout for a slow, aimed pour. It is the difference between pouring on the coffee and pouring at it.
Immersion
Brewing where the coffee sits in the water the whole time, like a french press or cold brew.
Percolation
Brewing where water passes through the coffee bed and leaves, like a pour over or drip machine.
Cupping
The standard tasting method: coarse grounds steeped in hot water, the crust broken and skimmed, then slurped from a spoon to judge a coffee. Read more.
Single origin
Coffee from one farm, region or country, rather than blended. Sold on its distinctive character rather than consistency.
Blend
Coffee combined from several origins for a consistent, repeatable flavour. Most espresso on cafe bars is a blend.
Washed process
Fruit removed from the bean before drying. Usually cleaner and more acidic in the cup.
Natural process
The cherry dried whole with the bean inside. Usually fruitier and heavier, and more variable.
Honey process
Some fruit mucilage left on the bean during drying. Sits between washed and natural in sweetness and body.
First crack
The audible crack during roasting when moisture escapes and the bean expands. Light roasts are dropped shortly after it.
Second crack
A later, quieter crack as the bean structure breaks down further. Dark roasts run into or past it.
Degassing
The days after roasting when beans release carbon dioxide. Espresso pulled from very fresh beans often gushes or tastes hollow.
Microfoam
Steamed milk with bubbles so small the surface looks like wet paint. It is what makes latte art possible and what makes milk taste sweet. Read more.
Steam wand
The pipe that injects steam into milk. Purge it before and after every use, and wipe it immediately.
Backflush
Forcing water back through the group head with a blind basket, usually with detergent, to clear coffee oils.
Descale
Removing mineral scale from the boiler and water path. Different from cleaning, which removes coffee oils. Both are needed. Read more.
Group head
The part of the machine the portafilter locks into, where water meets coffee.
PID
A temperature controller that holds brew water within a narrow band, instead of letting a thermostat swing.
Thermoblock
A fast-heating element that heats water on demand rather than holding a tank hot. Quick to start, less stable under load.
Knock box
The bin you knock the spent puck into. Saves your bin and your plumbing.
Ratios shown are the common working figures used throughout this site: about 1:2 for espresso (18g in, 36g out) and about 1:16 for pour over. They are starting points to dial from, not rules.