Espresso Glossary

This glossary is designed to sit before the rest of the espresso series. It is not a “how-to” guide and it is not Barista 101 in the broad sense. Its purpose is to give readers a shared language so that when terms appear in later volumes, they can be understood without confusion or guesswork.

Espresso education often fails not because concepts are too advanced, but because people are expected to understand discussions without first being taught the vocabulary. This glossary exists to solve that problem.

Use it as a reference. Return to it often.

A

Automatic espresso machine
An espresso machine that controls water volume or shot time automatically. The user grinds, doses, and tamps, but the machine stops the shot based on pre-programmed parameters.

B

Backflush / Backflushing
A cleaning process where water is forced backward through the group head using a blind basket. This removes coffee oils and residue from the machine’s internal pathways.

Basket (Filter basket)
The metal insert that fits inside a portafilter and holds ground coffee. Baskets are engineered for specific dose ranges and play a critical role in extraction behavior.

Bean density
A characteristic influenced by origin, processing, and roast level. Denser beans often require finer grinding and more deliberate extraction conditions.

Bottomless portafilter (Naked portafilter)
A portafilter with the spouts removed, exposing the basket. Used to visually observe extraction behavior, including channeling and uneven flow.

C

Channeling
Uneven water flow through the espresso puck, where water finds paths of least resistance. This leads to under-extraction in some areas and over-extraction in others.

Coffee puck
The compacted bed of ground coffee after extraction. Its condition can offer clues about extraction quality, but it is not a definitive diagnostic tool on its own.

Commercial espresso machine
A machine designed for café environments, built for temperature stability, durability, and high-volume service. Typically paired with commercial grinders.

D

Dialing in
The process of adjusting grind size (and sometimes dose) to achieve a balanced extraction with a specific coffee on a specific machine. In professional contexts, this is typically brief and deliberate, not endless.

Dose
The mass of dry ground coffee placed into the basket. Dose is constrained by basket design and should not be treated as a universal constant.

E

Espresso
A concentrated coffee beverage produced by forcing hot water through finely ground coffee under pressure. Espresso is both a brewing method and a beverage category, not a roast level.

Espresso roast
A marketing term rather than a technical classification. It generally refers to darker roasts intended to perform easily under espresso extraction but is not required for espresso brewing.

Extraction
The process by which soluble compounds are dissolved from coffee grounds into water. Over-extraction and under-extraction refer to imbalance, not time alone.

F

Flow rate
The speed at which espresso exits the portafilter during extraction. Flow rate is influenced by grind size, puck preparation, and machine behavior.

G

Grinder
A device that reduces coffee beans into particles. In espresso, grinder quality and consistency have a greater impact on results than most other variables.

Grind size
The relative fineness or coarseness of ground coffee. Espresso requires a fine grind, but the exact setting depends on the grinder, coffee, and machine.

Group head
The part of the espresso machine where hot water exits and enters the portafilter. It is a critical thermal and mechanical interface in the system.

H

Heat exchanger (HX)
A machine design that uses a single boiler with a heat exchanger tube to brew espresso while maintaining steam capability. Requires flushing for temperature management.

I

Italian espresso tradition
A style of espresso culture emphasizing consistency, speed, and balance. Historically associated with lower doses, darker roasts, and service-focused workflows.

M

Manual espresso machine
A machine that requires the user to control most variables, including shot start and stop. Some manual machines also allow pressure profiling.

P

Particle distribution
The range of particle sizes produced by a grinder. Narrow, consistent distributions support stable extraction; wide distributions introduce inconsistency.

Portafilter
The handled device that locks into the group head and holds the basket. Portafilters come in different diameters and styles depending on the machine.

Pressure
The force used to push water through the coffee puck. In espresso, pressure is a result of resistance, not an independent goal.

Pre-infusion
A phase where water is introduced at lower pressure before full extraction begins. Intended to saturate the puck more evenly.

Pump
The component that moves water through the espresso machine. Common types include vibratory (vibe) pumps and rotary pumps, each with different performance characteristics.

R

Ratio (Brew ratio)
The relationship between dry coffee mass and liquid espresso mass. Ratios describe extraction outcomes; they do not define espresso universally.

Roast level
A classification describing how long coffee beans have been roasted. Roast level affects solubility, flavor, and extraction behavior.

S

Semi-automatic espresso machine
A machine where the user starts and stops the shot manually but does not control pressure or temperature directly.

Shot time
The duration of espresso extraction. Time is an observational metric, not a standalone indicator of quality.

Single boiler
A machine design using one boiler for both brewing and steaming. Requires temperature changes between functions.

T

Tamping
Compressing ground coffee in the basket to create an even surface and resistance. Consistency matters more than force.

Thermal stability
A machine’s ability to maintain consistent brewing temperature. Greater stability generally supports repeatable extraction.

U

Under-extraction
A condition where insufficient soluble material is extracted from the coffee, often resulting in sour or thin flavor.

V

Vibratory pump (Vibe pump)
A compact pump commonly used in home espresso machines. It is louder and less pressure-stable than rotary pumps but effective within its design scope.

W

Water chemistry
The mineral composition of brewing water. Water quality affects extraction, flavor, and machine longevity.