Coffee Brewing GlossaryAn Almost Comprehensive Glossary of Brewing Terms
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The acid commonly associated with vinegar, giving marinades, mustard, ketchup, vinaigrettes, and salad dressings their tang. In coffee and other food products it is often a byproduct of fermentation.
The bright, tart sensation that enlivens the taste of coffee: without acidity, coffee is dull and flat. Acids are chemical compounds that react with bases and contribute to acidity by donating hydrogen ions (protons). Coffee generally has a slightly acidic pH around 5, however, this measurement is generally unrelated to the sensory analysis of perceived acidity. There are many different types of organic acids that can be found in coffee, the most commonly discussed being malic, citric, tartaric, lactic, and acetic acids, although quinic and chlorogenic acids appear in much higher concentration.
Any lingering flavor experienced after the food or drink is consumed. A pleasant aftertaste is a defining quality of coffee. Also called the “finish”, this sensation is heavily impacted by retronasal olfaction.
The smells produced by a brewed coffee, which can be perceived either orthonasally or retronasally. In cupping, aroma also refers specifically to the smell of brewed coffee, as opposed to the smell of dry coffee, which is referred to as fragrance.
Auto Volumetric (AV) Espresso Machine
A machine that can be programed by the barista to dispense a precise amount of brew water through the puck at the touch of a button, saving the barista from having to stop the shot manually. AV machines may also have scales built into the drip tray, which measure the brew yield of the espresso and can be programmed to reach a specific yield.
A coffee professional responsible for brewing and serving a variety of delicious beverages from behind the counters of coffee establishments.
One of the five basic taste sensations. Though often perceived as unpleasant, bitterness is an inherent characteristic in coffee. Bitterness arises from several compounds in a coffee, including caffeine, melanoidins, tannins, and many others.
This is a physical and visual change in the stream of espresso dripping into the demitasse, due to there being fewer solubles at the end of an extraction than the beginning. At the start of a shot, the stream—full of coffee solids washed out of the grounds—will look rich reddish-brown, whereas during blonding it becomes paler and golden-yellow.
The first phase in an infusion brew. A small amount of water is poured over the coffee grounds in order to fully saturate the grounds and release some of the CO2 . This allows for less turbulence and more even extraction in the rest of the brew. Sometimes called preinfusion, particularly when brewing espresso.
A description of a coffee’s mouthfeel. It can be described using its heaviness, tactility, or feeling of thickness in the mouth and throat.
The part of a brew device that holds ground coffee and allows water to drain through the brew bed. In an espresso portafilter, the brew basket also acts as the filter, with perforated by many precisely placed holes directly in the basket. Other brewers – especially batch brewers – have baskets that are designed to hold a paper filter and usually have a few large drainage holes.
Grounds that settle to the bottom of the brewer during and after extraction, forming a sedimentary base. An evenly extracted brew bed usually looks superficially flat when the brew water has drained out.
Flat rubber rings used in the group head of an espresso machine to seal the portafilter into the group head. The gasket creates a tight seal, preserving pressure and preventing water from leaking out during the brew.
A specific coffee and water dose, often with precise pulse pours and desired total brew time, that produces a delicious cup. Finding the right brew recipe can take some trial and error, referred to as “finding a dial” or “dialing–in”.
How much coffee liquor ends up in the cup after extraction.
Metal or ceramic plates inside a grinder, spaced a precise distance apart, in order to grind coffee beans. One burr is usually fixed while the other rotates. The mobile burr may be moved to adjust grind size by getting closer to or further away from the fixed burr. Burr shape and sharpness can affect grind consistency; the two most common are flat burrs and conical burrs. Burrs should be regularly maintained: follow manufacturer instructions for proper maintenance.
A non-enzymatic sugar browning reaction brought on by thermal decomposition which results in sweet, nutty flavors and brown color.
The uneven movement of water through a brew bed, caused by uneven distribution, collections of fines, and/or pockets of empty space. Distribution and/or careful tamping can disperse the grounds so that water drains through the brew bed or puck evenly. Water follows paths of least resistance and will be affected by small variations in the coffee distribution. This can result in an uneven extraction of espresso, as well as a mixture of over- and under-extracted tastes.
A family of acids found in green and roasted coffee, consisting of more than six individual acidic compounds. The primary six are grouped into two main categories: mono-caffeoyl and di-caffeoyl. Di-caffeoyl does not break down during roasting, and it imparts a metallic taste when present in coffee. During the roasting process, mono-caffeoyl breaks down slowly, while quinic and caffeic acid level increase. This decomposition increases during later stages of roast development, and if taken too far you end up with a harsh, unpleasant phenolic flavor.
The inability of a brew bed to drain water during an infusion brew, typically when fines clog the bottom of the bed to the point that drainage is significantly restricted.
The acid found naturally in citrus fruits like lemons and limes. Citric acid produces a tart, sour taste.
Small (<1 um) undissolved particles dispersed through a liquid. Unlike particles in suspension, colloids are so small that they do not settle out due to gravity and cannot be separated out through filtering or centrifuging. The colloids in milk create the Tyndall Effect, making milk look opaque and bluish-white to our eye.
Conical Burr Grinder
Conical burrs have one cone-shaped burr that sits inside another hollow cone-shaped burr. These two cones face downwards, and beans are sent through the space between them, which can be adjusted.
The light-colored foam that sits on top of a shot of espresso. Crema is a naturally produced emulsion of gas and oil which quickly dissipates. It is an essential part of traditional espresso.
A widely used method of evaluating coffee quality for professional purposes. Standard amounts of coffee are brewed with a simple immersion brew method in cupping bowls, which can then be sampled with spoons. Cupping includes evaluation of fragrance, aroma, flavor, acidity, body, defects, sensorial descriptors. While standardized cupping procedures have been established by organizations such as the SCA and CQI, there are many different cupping forms that professional cuppers use.
Days Off Roast
The number of days since a roasted coffee has been roasted.
The slow escape of carbon dioxide and nitrogen, among other gasses, from coffee after roasting. Coffee begins degassing as soon as it exits the roaster and begins to cool. For a few hours to a few days after roast, the coffee may be too gassy to extract evenly, and may negatively impact the flavor of the brew. This can be seen by observing the bloom phase of a pour–over. In a fresh, gassy coffee, there will be a lot of expansion, agitation, and bubbling, which actively disturbs coffee distribution and even extraction. Within two to four weeks the coffee has mostly off-gassed. This can be witnessed during the bloom phase of a pour–over as well, where instead of forming a dome, the coffee grounds remain flat, with no expansion or bubbles.
A small cup used to serve espresso. A demitasse typically holds two to three ounces but may be larger or smaller depending on custom and style preferences.
The process of finding a favorable brew recipe of a given coffee, either for personal use or for a period of service. Typically, a barista will repeatedly brew a coffee, carefully manipulating variables with each extraction and evaluate each cup before choosing the recipe that produces the best flavors.
The way that a dose of coffee is settled into its filter. In preparing espresso, a barista may use their finger or a special tool to distribute the coffee evenly in the portafilter before tamping.
The amount of dry coffee grounds used in a brew, usually measured by mass.
A substance that helps stabilize an emulsion.
A suspension of one liquid in another, in which neither liquid is fully dissolved but instead one is finely dispersed throughout the other.
The process of injecting air into the body of liquid so that the air is held in suspension.
Brewed coffee produced under pressure in a specialized machine. In specialty coffee, espresso is usually a small beverage, between 20-40g (0.75-2oz), made from finely ground coffee, and brewed under 8-10 bars of pressure with a very short brew time, usually 25 to 40 seconds.
Refers to the brew bed of an espresso in the portafilter, so-called because of its distinct disk-like shape.
The coffee solids removed from the coffee grounds and flushed into the brew liquid. This can be measured as a percentage of the mass of the dose, i.e., “This brew yielded a 20% extraction”, where the extraction percentage is a function of how many dissolved solids are suspended in the brew liquid, and how much mass was removed from the original dose of ground coffee. In specialty coffee, between 18 and 22 percent is often considered “ideal.” The barista must manipulate and control the rate of extraction for efficiency and taste.
Extraction Yield Percentage
The percentage by mass of coffee solids that are dissolved into brewed coffee. Extraction yield %= Beverage Weight (g) x TDS / Coffee Dose (g)
A semi-permeable barrier. Coffee filters are generally made from paper or metal, which allow liquid and dissolved solids to pass through but not coffee grounds.
Fines are tiny particles of ground coffee. Roasting makes the coffee’s cellulose brittle, and grinding may shatter it into various sizes. A natural byproduct of this shattering are tiny particles of coffee made up of cell fragments. Although fines will almost always form some percentage of coffee grounds, an excess in fines will create choking and over-extraction. The presence of fines can be limited by using sharp, well calibrated burrs and keeping the grind from getting too fine.
Flat Burr Grinder
Flat burr grinders have two rings of burrs which face each other. Coffee is passed between the rings, which are adjusted to a precise distance. Flat burrs generally cause less shattering, and therefore less fines are created with a flat burr grinder.
A fragrance is simply the unit of smell or the scent of something. It can only be perceived through our nasal cavity. In cupping, fragrance refers specifically to the smell of dry coffee before adding brew water.
The size of the coffee grounds affects how much resistance the water encounters as it is pushed through the grounds. Smaller grind size results in a higher surface area, meaning that more of the coffee is exposed to the water and will therefore extract faster. Smaller grind size will also restrict the flow of water as it passes through the brew bed, so that water and coffee spend more time in contact with each other.
The chamber on an espresso machine where coffee grounds are brewed, sometimes referred to as the brew head. It is pressurized and sealed with a brew gasket once the portafilter is locked into place. The portafilter is inserted into the group head, where it gets showered with pressurized hot water.
High-Temperature Short-Time (HTST) Pasteurization
A method of heat pasteurization used for perishable beverages like fruit and vegetable juices, beer, kosher wine, and some dairy products such as milk. This is sometimes also called flash pasteurization. The product is heated to a required minimum temperature and held at that temperature for the required time. In the United States dairies are required to heat milk to at least 161F for 15 seconds. This is followed by immediate cooling of the milk. Milk is pasteurized to kill any pathogenic bacteria that may be present.
The process by which two or more substances insoluble to each other can be mixed into a permanent emulsion. In homogenized milk, fat droplets are emulsified so that the cream does not separate.
A brew method wherein the grounds are submerged in the total volume of brew water. A filter may be used to remove the grounds once extraction is complete, or they may simply be allowed to settle or be pushed down to the bottom of the brewer. The rate of extraction will slow over time as the water reaches saturation.
A brew method wherein water flows through a bed of coffee grounds before passing through a filter, with the addition of fresh hot water with either in a continuous stream or in each pulse pour. Infusion brewing extracts coffee solids more efficiently because fresh hot water is continually added to the brew bed.
Lactic acid is characterized by the way it changes the mouthfeel of coffee, making for a smoother body and causing it to feel slightly creamy in nature, as opposed to the bright intensity of citric or malic acids. Lactic acid fermentation is an important stage in processing many coffees.
A large group of organic substances that do not dissolve in water; these include fats, oils, hormones, and certain components of membranes.
Liquid Retained Ratio (LRR)
The measurement of water absorbed and retained by coffee grounds during brewing. A barista can measure the brew yield to determine how much of the brew water was retained and use the difference between these two divided by the coffee dose to find the exact LRR (LRR=[brew water – brew yield]/coffee dose). Industry standard assumes a ratio of 2 grams of water per 1 gram of coffee grounds.
Another word for the brewed coffee liquid.
The acid found naturally in green apples, pears, and cherries. It can be said to have a smoother mouthfeel than other acids but retains a tart taste.
Manual Espresso Machine
As opposed to a semi-automatic espresso machine, these machines feature a lever attached to an internal spring and piston assembly. The barista pulls the lever to engage the assembly and must then manually release the lever in order to force hot water through the grounds at high pressure.
The complex, brown-colored compounds formed when sugars and amino acids combine during caramelization. This is what gives coffee (or anything that has been caramelized) its characteristic brown color, and may contribute to the mouthfeel of a brewed coffee.
A foam composed of very small, uniformly sized bubbles having a diameter usually less than 500 μm.
The tactile qualities of coffee liquor in the mouth. Mouthfeel refers to texture and physical sensation on the palate and is one of the fundamental attributes of coffee’s sensory analysis. Some qualities of mouthfeel include mouth drying, coating, smooth, astringent, and many others.
The perception of odors from particles inhaled through the nostrils.
A process through which a product is treated with heat to eliminate pathogens and extend shelf life. In the US, cow’s milk is often pasteurized through High Temperature Short Time (HTST) sometimes called flash pasteurization, but there are many alternate methods.
A portable filter with handle used to brew espresso. This part of the espresso machine houses the basket and locks into the group head. Spouted portafilters allow the barista to split shots, meaning the shot runs down two channels attached to the bottom of the filter. Bottomless portafilters let the barista observe the espresso as it extracts directly out of the basket.
The espresso brew basket, a metal filter which holds the ground coffee and allows pressurized water to filter through it. While they must be a specific diameter to fit in their portafilter, baskets can be deep or shallow often indicated by the terms single or double (or even triple), and in all cases are intended for a specific dose of ground coffee. These baskets’ filters are made up of perforations that are precisely punched for consistent extraction. The basket may also be blank, meaning there is no filtration or perforation, which forces hot water back into the machine; blank portafilters are used exclusively for cleaning and maintenance.
A method of infusion brewing made by pouring water, usually by hand, over a bed of coffee set in a filter.
Preinfusion works under the same principles as the bloom phase of a pour–over, using a small amount of water to saturate the grounds for the first few seconds of brewing. This can help release gasses that might cause turbulence and prevent even extraction. The word preinfusion is often used to refer to espresso, while “bloom” is more often used to refer to pour–over and other methods.
Refers to the use of multiple incremental pours of hot water added to an infusion brew after the bloom, rather than a continuous stream. A pulse pour adds fresh, unsaturated water to the brew bed, which can extract more soluble material from the grounds.
A phenolic compound often formed as a byproduct of the decomposition of chlorogenic acid. During the roast process, quinic acid levels increase as the levels of chlorogenic acid decrease. Quinic acid, along with citric and malic, make up a large portion of coffee’s acid content.
A device used to measure the Total Dissolved Solids in a liquid. Refractometers measure TDS by interpreting refracted light through a liquid solution. The number of solids suspended in a liquid affects the way light is refracted through it, allowing for an accurate reading of their concentration.
The perception of odors from particles inhaled through the back of the oral cavity, such as when eating or drinking. Retronasal smell is critical for experiencing flavor and aftertaste.
An espresso produced by using more coffee and restricting the amount of water that passes through. Ristretto is an Italian word meaning “restrained.”
One of the five basic taste sensations. Saltiness may arise in coffee as a result of poor extraction, or from an excess of minerals in the brew water. It is not a result of natural salts in the coffee but occurs from a combination of other compounds and chemicals.
Semi-Automatic Espresso Machine
An espresso machine that is controlled by the barista, who must start and stop the shot manually by pressing a button or sliding a paddle.
A method of immersion brew involving two stacked chambers and a cloth filter connecting them. The barista heats the water in the bottom chamber with a burner or flame, and the boiling water’s own vapor pressure forces the water to rise through the filter and into the upper chamber where it is mixed with the coffee grounds. After the coffee extracts, the barista removes the flame and the resulting vacuum from the cooling empty chamber pulls the coffee through the filter back down into the lower chamber, which can then be used as a decanter.
The capacity and degree to which a substance, like ground coffee, will dissolve (or extract, as we say) into a solute, like water, to create a solution, like brewed coffee. Coffee’s maximum solubility is about 30%, but its “ideal” extraction is somewhat less, often stated as between 18-22%.
Another of the five basic tastes, this is the flavor experience of something very acidic, which may cause the palate to pucker. Citric acid is the most classic example of this taste, but sourness can be a result of any number of factors. It is usually not desired in coffee, or if present, must be balanced by sweetness and bitterness.
The part of an espresso machine used for aerating and steaming milk. A thin metal tube connected to the steam boiler and perforated at the end to allow the manual release of steam. The steam boiler, which in newer machines is often separate from the brew boiler, heats water to the point of creating steam. In milk steaming, the steam is entrained into the milk, and then releases heat as it condenses back into liquid form, quickly heating the milk even further.
A ‘surface active agent’ which lowers the surface tension between substances. An emulsifier is a kind of surfactant which helps with foam stability.
One of the five basic taste sensations, usually associated with the presence of sucrose. Sweetness is an essential characteristic in coffee, arising from natural sugars and sugar browning in the coffee bean.
A device used by the barista to flatten or compact the bed of coffee grounds in a portafilter basket. Tampers are usually flat bottomed, although they can be rounded or ridged. Tamping is the act of using the tamper.
The acid most associated with grapes and berries, but also found in bananas, tamarinds, avocados, and apricots. Tartaric acid is sometimes added to foods to give it a sour taste, and acts as an antioxidant.
TDS (Total Dissolved Solids)
A measure of all particles suspended in a liquid solution. TDS can help indicate the strength of a brew and is a critical measurement used to obtain Extraction Yield Percentage. For liquid coffee, TDS is usually expressed in parts per thousand (ppt), or as a percentage. 1.25 ppt is equal to 1.25% solids.
Total Brew Time
The length of time a coffee takes to brew, typically measured from the first drop of water hitting the brew bed until the last of the brew water finishes dripping through the brew device. Total brew time can vary significantly depending on grind size, pour technique, and brew method. Knowing how long it takes for a brewed coffee to reach the desired yield is important for understanding how accurate your dial is and how to manipulate the brew to achieve desired extraction.
Light scattering by particles in a colloid or a very fine suspension. The Tyndall effect gives milk its translucent bluish-white appearance, as well as makes the sky blue, and light beams visible in fog.
Ultra-heat treatment (UHT)
A fast, high-temperature method of pasteurizing milk which makes it shelf stable for several months if stored in a sealed package.
One of the five basic tastes, Umami describes savory sensations related to glutamates – for example mono-sodium glutamate, or MSG. Although sweetness is usually prized above all, a coffee with savory notes can bring nuance and balance to the cup.
General industry recommendation for water temperature when brewing coffee is from 195 to 205 F. Hot water extracts coffee at a faster rate. Water is a polar molecule, meaning it has an uneven distribution of electron density and is eager to attach itself to other molecules, thereby extracting them. Heat makes the water molecules vibrate faster, making them even more attracted to other molecules. Water that’s too hot can extract the coffee too quickly or efficiently and lead to unpleasant flavors, while water that’s too cold won’t be able to penetrate the grounds sufficiently to extract solids in a reasonable brew time.
The amount of liquor produced by brewing, measured either by weight or by volume. Knowing the exact brew yield is particularly important when dialing in espresso, while we often assume the brew yields in infusion and immersion brews. By keeping an eye on dose and yield the barista will be aware of what ratio they are brewing to and thus be able to control total extraction.