Coffee & Espresso Glossary

A unit of pressure. Espresso is typically extracted at around 9 bar, though most home machine pumps are rated higher (often 15 bar) to maintain 9 bar under load.

Uneven water flow through the coffee puck — usually caused by an uneven tamp, an inconsistent grind, or clumped grounds — that lets water rush through the path of least resistance instead of extracting evenly.

The golden-brown foam that sits on top of a well-pulled espresso shot, formed from emulsified coffee oils and the CO2 released during extraction.

The process of dissolving flavour compounds out of ground coffee using hot water under pressure — "over-extracted" and "under-extracted" describe shots where too much or too little has been pulled from the grounds.

The part of an espresso machine where the portafilter locks in, and through which hot water is delivered into the coffee.

The handled fitting that holds the coffee basket and locks into the group head. See our coffee machine buying guide for why 58mm portafilters matter.

The compacted disc of spent coffee grounds left in the basket after a shot — a wet, uneven, or cratered puck usually points to a channelling or tamping issue.

Informal terms for making an espresso. "Pulling a shot" dates back to manual lever machines, where you physically pulled a lever to force water through the coffee.

A widely used group-head design dating back to 1961, known for thermosiphon circulation that helps keep brew temperature stable without electronic control.

A mechanism found on some grinders (mostly older commercial models) that dispenses a measured dose of ground coffee via a lever, rather than grinding straight into the portafilter.

Grinding only the exact amount of beans needed for one brew, rather than keeping beans sitting in a hopper — useful for anyone rotating between different coffees.

The amount of ground coffee left behind inside a grinder's chute or burrs between doses. Lower retention matters most if you switch beans often, so old grounds don't mix into the next dose.

The process of adjusting grind size, dose, and shot time together until a shot tastes balanced for a specific bean. See our espresso dosing guide for the full process.

Using a fine-needle tool to break up clumps in the grounds before tamping, so water extracts evenly instead of channelling through compacted lumps.

One of the two major commercial coffee species, generally regarded as producing more nuanced, complex flavour. Most specialty coffee is Arabica.

The other major commercial species — higher in caffeine, generally more bitter, and traditionally used for cheaper blends, though quality Robusta is increasingly used in some espresso blends for body and crema.

Coffee sourced from one specific farm, region, or country, rather than blended with beans from elsewhere.

A mix of beans from different origins or roast levels, combined to achieve a specific flavour profile, consistency, or price point.

A quality classification for coffee that scores highly against cupping (tasting) criteria and is generally free of processing defects.

The release of CO2 from beans after roasting. Freshly roasted coffee is often rested for a few days before brewing so degassing doesn't interfere with extraction.

Audible cracking sounds during roasting that mark key stages — first crack signals the start of a drinkable roast, and second crack (if reached) signals a darker roast level.

Unroasted coffee beans, as they exist before roasting turns them brown and develops their flavour.

Mineral deposits — mostly calcium and magnesium — that build up inside a machine's boiler and water lines over time, caused by hard water. See our descaling guide for how to deal with it.

Water with a high mineral content — the main cause of scale buildup in coffee machines.

A device that reduces the mineral content of water before it reaches the machine, slowing scale buildup. See Coffee Machine Water Filters NZ for whether you need one.

Running water or a cleaning solution back through the group head's internal valve using a blind (solid) filter basket, to clear coffee oil buildup a normal rinse can't reach.

The sensation of weight, thickness, or richness a coffee has in the mouth — light-bodied coffees feel more like tea, full-bodied coffees feel heavier and creamier.

The bright, tangy quality in coffee — distinct from the unpleasant sourness caused by under-extraction — often described as fruity or wine-like in good specialty coffee.

The smell of brewed coffee, which plays a major role in how flavour is actually perceived.

The flavour that lingers in the mouth after swallowing — can be clean and pleasant, or bitter and drying, depending on the bean and extraction.