Reference

Glossary

Short, plain-English definitions. Each term links to the guides that cover it properly.

A

AISI 304 stainless steel · also 304 stainless: A common stainless steel grade named in accessory listings; Normcore's WDT needles, for example, are 304 stainless. The grade alone does not establish US food-contact compliance, which depends on the finished article's substances and use. Read more: Buying espresso accessories on AliExpress: what to check, Buying and safety

B

Backflush · also backflushing: Cleaning the group by locking in a basket with no holes, or a cleaning disc, so water, and sometimes cleaner, is pushed back through the group. Only do it on machines whose manual describes it: Breville, Profitec and ECM each publish their own procedure. Read more: How to backflush an espresso machine, Cafiza vs descaler: which does what?, Cleaning and maintenance
Bar (pressure): A unit of pressure, close to the air pressure at sea level, used to describe brewing pressure. Cafelat suggests starting at 6-7 bar on its Robot.
Basket · also filter basket, filter: The removable perforated metal cup that sits in the portafilter and holds the coffee. Its inside diameter decides which tamper and puck screen fit; IMS's Breville baskets, for example, measure 54 mm inside and take a 53 or 53.4 mm tamper. Read more: Espresso basket and tamper size guide, Precision espresso baskets explained, Baskets and portafilters
Basket height · also basket depth: How deep a basket is, which sets how much coffee it holds. IMS's B70 baskets, for example, come in 22.5 to 28.5 mm heights, with dose ranges rising with height. Read more: Precision espresso baskets explained, Baskets and portafilters
Bellows · also grinder bellows, blower: A flexible cap fitted to some grinders that you press to puff air through and push out retained grounds. Use one only if your grinder's maker allows it. Read more: Grinder accessories
Blind basket · also blind filter, backflush basket: A basket with no holes, used in place of the normal basket to backflush the group. Lelit, Profitec and ECM include one with machines such as the Mara X, GO 2.0 and Classika PID. Read more: How to backflush an espresso machine, Cleaning and maintenance
Blind shaker · also shaker: A closed cup that you grind into and shake to mix the grounds before tipping them into the basket, used as an alternative or extra step to needle distribution. Read more: What is WDT?, Distribution and WDT
Bottomless portafilter · also naked portafilter: A portafilter with the bottom cut away so the underside of the basket is visible during a shot. It must lock into your machine's group, so buy one listed for your model: the locking ears matter, not just the diameter. Read more: Bottomless portafilters by machine, Why does my bottomless portafilter spray?, Why won't my portafilter lock in?, Baskets and portafilters
Brew ratio · also espresso ratio: The weight of coffee in compared with the weight of espresso out, written like 1:2. Cafelat's example for the Robot is 16 g in and 32 g out; no single ratio is right for every coffee. Read more: Espresso ratio calculator, Scales and weighing
Burrs · also grinder burrs: The pair of hard, ridged discs or cones in a grinder that crush beans to a set gap. Grind size changes as the gap between them is made smaller or larger. Read more: Grinder accessories

C

Calibrated tamper · also spring-loaded tamper, constant-pressure tamper: A tamper with a spring or click mechanism that gives way at a set force, so each tamp is pressed about equally hard. Normcore's V4, for example, ships with 15, 25 and 30 lb springs. Socratic Coffee found no TDS difference between tamps of 5 and 20 kg. Read more: Calibrated, spring-loaded or impact tamper?, How hard should you tamp espresso?, ALIKISSCAFE 30 lb calibrated tamper: research notes, Tampers and tamping
Channeling: When water finds an easier path through part of the coffee bed, so some coffee is over-extracted and the rest under-extracted. Cameron and colleagues (Matter, 2020) found uneven flow at very fine grind settings, which lowered extraction and made shots less reproducible. Read more: Why does my bottomless portafilter spray?
Cleaning disc · also backflush disc: A disc supplied by Breville that blocks the basket for the cleaning cycle. Breville's Barista Express guide uses it with the 1 CUP basket and one cleaning tablet when the CLEAN ME light shows. Read more: How to backflush an espresso machine, Cleaning and maintenance
Clear water backflush · also water backflush: A backflush with water only, no cleaner. Breville's Barista Express tutorial recommends one after each brewing session to clear loose grounds, coffee oils and other residue. Read more: How to backflush an espresso machine, Cleaning and maintenance
Crema: The layer of fine foam on top of a freshly made espresso.
CUSMA (Canada) · also USMCA: The Canada-United States-Mexico Agreement. Its higher courier thresholds apply only to qualifying goods from the US or Mexico; courier and mail goods from other countries, such as China, are duty and tax free only up to C$20. Read more: Buying espresso accessories on AliExpress: what to check, Buying and safety

D

De minimis (US): The US duty-free allowance for low-value imports. CBP says it ended for goods from all countries on August 29, 2025 and remains suspended for goods of $800 or less arriving by any mode, including mail. Read more: Buying espresso accessories on AliExpress: what to check, Buying and safety
Descaling · also decalcifying: Removing mineral scale left by hard water from a machine's boiler and water path, using a descaling product. It is a different job from cleaning coffee oils: Breville's guide says its cleaning cycle is separate from descaling. Read more: Cafiza vs descaler: which does what?, Cleaning and maintenance
Dialing in · also dial in: Adjusting grind size, dose and yield, one at a time, until a coffee tastes the way you want on your machine. Read more: Espresso ratio calculator
Distribution: Spreading the ground coffee evenly through the basket before tamping, by tapping, stirring with needles (WDT) or using a distributor. The aim is a bed of even density that water flows through uniformly. Read more: What is WDT?, Needle WDT tool vs three-slope distributor, Distribution and WDT
Distributor · also leveler, spinning distributor, OCD: A tool that rests on the basket and is turned to level the top of the coffee before tamping. In Socratic Coffee's test, the OCD and OCD 2 distributors lowered extraction compared with using no distributor. Read more: Needle WDT tool vs three-slope distributor, What is WDT?, Distribution and WDT
Dose · also coffee dose, dry dose: The weight of ground coffee in the basket. Machine makers give one for their baskets: Breville lists 18 g for the Bambino and Barista Express and 22 g for the Dual Boiler. Read more: Espresso ratio calculator, Precision espresso baskets explained, Dosing funnels and cups
Dosing cup: A cup you grind into and then tip into the basket, instead of grinding straight into the portafilter. Fit varies by machine: Normcore says its 53.3 mm dosing cup is not compatible with the Barista Express Impress. Read more: How to choose a dosing funnel, Dosing funnels and cups
Dosing funnel · also dosing ring: A ring that sits on the portafilter rim so grounds do not spill while you grind or stir. It is sold by portafilter size: Breville's own funnel is made for its 54 mm portafilters, and ECM's is 58 mm. Magnetic funnels also depend on the portafilter's material. Read more: How to choose a dosing funnel, Best dosing funnels for 51, 54 and 58 mm portafilters, Dosing funnels and cups
Dual boiler: A machine with separate boilers for brewing water and for steam, so each can be held at its own temperature.

E

E61 group · also E61: The Faema E61, a classic group-head design. ECM calls its own group a further development of it, and Rocket's catalog describes a redesigned E61 group; accessories sold as 'E61' are made for this group type. Not every 58 mm machine has one: Profitec calls the GO's group a ring brew group. Read more: Bottomless portafilters by machine, Espresso machine size finder
Espresso machine cleaner · also group cleaner, backflush detergent, Cafiza: A detergent for coffee oils and residue in the group, valves and lines, used with a blind basket. Urnex's Cafiza instructions call for up to 3 g per backflush, and its page does not mention descaling, which Breville treats as a separate job. Read more: Cafiza vs descaler: which does what?, How to backflush an espresso machine, Cleaning and maintenance
Espresso scale · also coffee scale: A small scale, usually with a built-in timer, for weighing dose and yield on the drip tray. Acaia's Lunar, for example, reads to 0.1 g with a 2 kg capacity. Read more: Best espresso scales with a timer and 0.1 g readout, Espresso scale accuracy vs resolution, Scales and weighing
Extraction: Dissolving flavor compounds and other solids from ground coffee into water. How much is dissolved is measured as extraction yield.
Extraction yield · also EY, extraction percentage: The percentage of the dry coffee's weight that ends up dissolved in the drink, worked out from TDS, drink weight and dose. Cameron and colleagues found it peaks and then falls as the grind gets very fine. Read more: How hard should you tamp espresso?, Espresso ratio calculator

F

FCC ID · also FCC certification: A US equipment authorization code. Devices that intentionally transmit radio signals must, with some exemptions, be certified by the FCC or a certification body before they are marketed in the US; we take this to include Bluetooth scales. An FCC ID is not a food-safety or quality mark. Read more: Buying espresso accessories on AliExpress: what to check, Best espresso scales with a timer and 0.1 g readout, Buying and safety
Fines: The smallest particles produced when coffee is ground, much finer than the target grind size. Read more: Grinder accessories
Food-contact material · also food grade: Any material that touches food or drink, such as a basket, puck screen or dosing funnel. In the US its status depends on each substance that could migrate into food under its intended use, so 'food grade' wording on a listing does not prove compliance. Read more: Buying espresso accessories on AliExpress: what to check, Buying and safety
Free Return (AliExpress): An AliExpress service for listings that carry the 'Free Return' label: eligible buyers can ask to return an item without giving a reason within 15 calendar days of confirmed receipt. Returned items must be unused and undamaged, with original packaging. Read more: Buying espresso accessories on AliExpress: what to check, Buying and safety

G

Grind size: How fine or coarse the coffee is ground. Finer is not always better: Cameron and colleagues found extraction peaks and then falls at very fine settings. Read more: Why does my bottomless portafilter spray?, Grinder accessories
Group brush: A brush with an angled head for scrubbing coffee grounds off the shower screen and group gasket. Read more: How to backflush an espresso machine, Cleaning and maintenance
Group gasket · also group seal: The rubber ring in the group head that the basket rim presses against to seal it during a shot. Read more: Why won't my portafilter lock in?, Cleaning and maintenance
Group head · also group, brew group: The part of the machine that the portafilter locks into and that delivers hot water through the shower screen. Its locking design decides which portafilters fit, so machines with the same basket size can still need different portafilters. Read more: Why won't my portafilter lock in?, Espresso machine size finder

H

Headspace: The gap between the top of the tamped coffee, or the puck screen, and the machine's shower screen once the portafilter is locked in. A bigger dose or a puck screen takes some of it up. Read more: Are puck screens worth it?, Why won't my portafilter lock in?, Puck screens

I

Inside diameter · also basket ID, fit diameter: The width across the inside of a basket at the depth where the coffee sits, which decides tamper and puck screen fit. Baskets can taper: Flair's standard Flair 58 basket is 58.7 mm at the top and 58.5 mm lower down. Read more: Espresso basket and tamper size guide, Espresso machine size finder, Baskets and portafilters

K

Knock box: A container with a padded bar that you knock the portafilter against to drop the spent puck.

L

Landed cost: The full cost of an imported item once shipping, duties, taxes and any fees are added to the listing price. Read more: Buying espresso accessories on AliExpress: what to check, Buying and safety
LELIT57: Lelit's name for the group and tool size of machines such as the Anna (PL41TEM). Lelit publishes no diameter; Normcore lists 57.5 mm tampers and 57 mm screens and funnels for these machines, not 58 mm tools. Read more: Espresso machine size finder, Espresso basket and tamper size guide
LELIT58 · also L58E: Lelit's name for the group and tool system of machines such as the Victoria, Mara X and Bianca; the Mara X and Bianca list an 'L58E' group. Lelit makes LELIT58 filters and filterholders and does not call the group E61, though Normcore's guide labels some of these machines E61. Read more: Espresso machine size finder
Lever machine · also manual lever: An espresso maker where brewing pressure comes from a lever, pulled by hand or driven by a spring, rather than an electric pump. Cafelat suggests aiming for 6-7 bar at first, which it measured on traditional lever machines.
Listing variant · also SKU option: One option within a marketplace listing, such as a size or color. Accessory listings often sell several basket sizes under one listing, so the variant you select at checkout decides what arrives. Read more: Buying espresso accessories on AliExpress: what to check, Buying and safety

M

Milk pitcher · also milk jug, frothing pitcher: A metal jug, usually stainless steel, for steaming and pouring milk.

N

Nominal size · also label size: The size a part is named or labeled with, as opposed to the size that actually fits. Breville calls the Barista Express tamper 54 mm while precision tools for its baskets are about 53.3 mm, and Cafelat calls its Robot baskets 58 mm though the Professional basket measures 57.8 mm inside. Read more: Espresso basket and tamper size guide, 58 mm, 58.4 mm or 58.5 mm tamper?, Espresso machine size finder, Tampers and tamping
NRTL · also Nationally Recognized Testing Laboratory: A private testing organization recognized by OSHA to certify products to safety standards; UL is one. OSHA says its recognition of an NRTL is not an endorsement of the equipment the lab certifies. Read more: Buying espresso accessories on AliExpress: what to check, Buying and safety

O

Open area: The share of the basket bottom that water can flow out through, set by hole size, number and spacing. VST keeps total open area within plus or minus 5%, and barista.tools argues that the number of holes alone does not determine extraction. Read more: Precision espresso baskets explained, Baskets and portafilters
Over-extraction: Dissolving more from the coffee than tastes good, often from a grind that is too fine or a shot that runs too long. Such shots are often described as bitter or drying.

P

PID controller · also PID: A temperature controller that adjusts heating in small steps to hold the boiler near a set temperature, instead of simply switching the heater on and off.
POM (acetal) · also polyoxymethylene: Polyoxymethylene, a hard, low-friction engineering plastic. Cafelat makes its Robot leveling tamper in POM as well as in stainless steel and aluminum.
Portafilter · also filter holder, filterholder: The handled holder that locks into the machine's group head and carries the basket. Its labeled size, such as 54 mm on Breville's Bambino or 58 mm on Rancilio's Silvia, names a family of baskets and tools, not the exact size of a tamper that fits. Read more: Espresso basket and tamper size guide, Why won't my portafilter lock in?, Baskets and portafilters
Portafilter ears · also lugs, locking ears: The tabs on a portafilter that lock it into the group head. Their number varies; sellers offer De'Longhi portafilters with two or three ears, so count yours before buying a replacement or bottomless one. Read more: Why won't my portafilter lock in?, Bottomless portafilters by machine, Baskets and portafilters
Pre-infusion · also preinfusion: Wetting the coffee at low pressure or flow for a short time before full brewing pressure. Some machines do it mechanically: Lelit's Mara X spec sheet, for example, lists a group with mechanical pre-infusion.
Precision basket · also competition basket: A basket made to tighter, published tolerances for hole size, hole placement and dimensions. VST, for example, says it measures every hole on every basket and keeps total open area within plus or minus 5%. Read more: Precision espresso baskets explained, Baskets and portafilters
Pressurized basket · also dual-wall basket, double-wall basket: A basket with a double wall and a small exit that restricts flow, instead of an open grid of holes. Breville's Barista Express guide says to use its Dual Wall baskets with pre-ground coffee and Single Wall baskets with fresh beans; Gaggia ships the Classic E24 with one pressurized and two traditional filters. Read more: Espresso basket and tamper size guide, Precision espresso baskets explained, Baskets and portafilters
Puck · also coffee bed: The bed of ground coffee in the basket, tamped before brewing and knocked out as a spent cake afterward. Read more: How hard should you tamp espresso?
Puck prep · also puck preparation: Everything done to the coffee between grinding and brewing: dosing, distribution such as WDT, tamping and, if you use one, adding a puck screen. Read more: What is WDT?, How hard should you tamp espresso?, Are puck screens worth it?, Distribution and WDT
Puck screen · also puck filter screen: A thin perforated disc, usually metal, laid on the tamped coffee before brewing. It sits between the coffee and the shower screen and takes up some headspace. Like a tamper, it is sized to the basket: Normcore lists 53.3 mm for Breville's 54 mm machines and 58.5 mm for many 58 mm machines. Read more: Are puck screens worth it?, Best puck screens for 51, 54 and 58 mm baskets, Puck screens
PVD coating · also titanium PVD: Physical vapor deposition: a thin, hard coating bonded to a metal part, used for colored finishes such as Normcore's titanium PVD tamper base. 'Titanium PVD' names the coating, not what the part is made of. Read more: Buying espresso accessories on AliExpress: what to check, Buying and safety

R

RDT (Ross Droplet Technique) · also bean spritzing: Adding a few drops of water to whole beans before grinding to cut down static and clinging grounds. Socratic Coffee found no significant TDS difference with RDT, and shot times may have been less consistent. Read more: Does RDT work?, Grinder accessories
Readability (scale resolution) · also resolution, readability: The smallest weight step a scale displays, such as 0.1 g. It is not the same as accuracy: Acaia lists the Lunar's readability and repeatability separately, both 0.1 g. Read more: Espresso scale accuracy vs resolution, Best espresso scales with a timer and 0.1 g readout, Scales and weighing
Refractometer: An instrument that estimates TDS by measuring how a sample of coffee bends light.
Repeatability: How closely a scale gives the same reading when the same weight is placed on it again. Acaia lists 0.1 g repeatability for the Lunar. Read more: Espresso scale accuracy vs resolution, Scales and weighing
Retention · also grinder retention: Ground coffee that stays inside a grinder after grinding and comes out with the next dose. It matters most when you single dose. Read more: Does RDT work?, Grinder accessories
Ridgeless basket: A basket made without the ring-shaped ridge pressed into the side wall of many baskets. IMS's Big Bang basket for Breville machines, for example, is flat-bottomed and ridgeless. Read more: Precision espresso baskets explained, Baskets and portafilters
Ring brew group: Profitec's description of the group on its GO 2.0, which Profitec does not call an E61. Accessories made for E61 groups, such as bottomless portafilters, are not automatically a fit. Read more: Bottomless portafilters by machine

S

Self-leveling tamper · also palm tamper, leveling tamper: A tamper with a collar that rests on the basket or portafilter rim, so the base stays flat while you press. Both the base and the collar have to suit your basket size. Read more: Calibrated, spring-loaded or impact tamper?, Best espresso tampers for 51, 54 and 58 mm baskets, Tampers and tamping
Shot time: How long a shot runs, from starting the pump or lever to stopping it. Changes from shot to shot can point to a change in grind, dose or puck prep. Read more: Espresso ratio calculator
Shower screen · also group screen: The perforated screen in the group head that spreads hot water over the coffee. It is machine-specific: IMS makes different shower screens for Breville's 54 mm and 58 mm groups. Read more: Are puck screens worth it?, Puck screens
Single basket · also 1-cup basket, single-shot basket: A small basket for one shot. IMS rates its 1-cup competition basket at 7-11 g depending on roast, while its 24.5 mm B70 basket is rated for 16-22.5 g. Read more: Precision espresso baskets explained, Baskets and portafilters
Single dosing · also single-dose grinding: Weighing out the beans for one shot and grinding all of them, instead of grinding from a full hopper. It goes with grinders and add-ons designed to leave little coffee behind. Read more: Does RDT work?, Espresso scale accuracy vs resolution, Grinder accessories
Single-dose hopper: A small hopper that replaces a grinder's standard bean hopper and holds just one dose at a time. Read more: Grinder accessories
Single-wall basket · also non-pressurized basket, traditional basket: An ordinary basket with an open grid of holes, where the coffee bed alone controls the flow. Breville recommends its Single Wall baskets for fresh beans, and precision baskets are this type. Read more: Precision espresso baskets explained, Baskets and portafilters
Spraying: Thin jets of espresso shooting sideways from the bottom of the basket, which a bottomless portafilter makes visible. Baristas usually read it as a sign of channeling. Read more: Why does my bottomless portafilter spray?
Static: Electric charge that builds up on coffee as it is ground, making grounds cling to the grinder and scatter. RDT is one way people try to reduce it. Read more: Does RDT work?, Grinder accessories

T

Tamper · also coffee tamper: The flat-based tool used to press ground coffee into an even bed in the basket. Choose it by the basket's inside diameter, not the portafilter label: VST, for example, specifies a 58.40 mm tamper for its 58 mm-class baskets. Read more: Calibrated, spring-loaded or impact tamper?, Best espresso tampers for 51, 54 and 58 mm baskets, 58 mm, 58.4 mm or 58.5 mm tamper?, Tampers and tamping
Tamping · also tamp, tamping pressure: Pressing the ground coffee into a firm, level bed before brewing. Socratic Coffee found no TDS difference between 5, 10, 15 and 20 kg tamps; Breville's Barista Express guide suggests 15 kg and Profitec's manual about 20 kg. Read more: How hard should you tamp espresso?, Tampers and tamping
Tamping station · also tamping mat, portafilter stand: A stand or mat that holds the portafilter steady and level while you tamp, and protects the counter. Read more: Tampers and tamping
Tare: Zeroing a scale with a container on it, so it shows only the weight of what you add next. Read more: Espresso scale accuracy vs resolution, Scales and weighing
TDS (total dissolved solids) · also strength: The share of the drink, by weight, that is dissolved coffee, usually read with a refractometer. Socratic Coffee used it to compare tamping pressures and distribution tools. Read more: How hard should you tamp espresso?, Needle WDT tool vs three-slope distributor

U

Under-extraction: Dissolving too little from the coffee, often from a grind that is too coarse or a shot that runs too fast. Such shots are often described as sour or thin.

W

WDT (Weiss Distribution Technique) · also needle distribution, WDT tool: Stirring the ground coffee in the basket with thin needles before tamping, to break up clumps and even out the bed. WDT tools hold several fine needles; Normcore's, for example, uses 0.25 mm stainless steel needles. Read more: What is WDT?, Needle WDT tool vs three-slope distributor, Best WDT tools for espresso, Distribution and WDT

Y

Yield · also beverage weight, drink weight: The weight of espresso in the cup. In Socratic Coffee's tamping test, the drink's weight, not how hard the coffee was tamped, drove TDS. Read more: Espresso ratio calculator, Espresso scale accuracy vs resolution, Scales and weighing