Brewing Glossary of Terms

Adjunct
Any unmalted grain or other fermentable ingredient used in the brewing process. Adjuncts used are typically either rice or corn, and can also include honey, syrups, and numerous other sources of fermentable carbohydrates.

Aeration
The action of introducing air or oxygen to the wort (unfermented beer) at various stages of the brewing process. Proper aeration before primary fermentation is vital to yeast health and vigorous fermentation. Aeration after fermentation is complete can result in beer off-flavors, including cardboard or paper aromas due to oxidation.

Alcohol by Volume (ABV)
A measurement of the alcohol content of a solution in terms of the percentage volume of alcohol per volume of beer. To calculate the approximate volumetric alcohol content, subtract the final gravity from the original gravity and divide by 0.0075. For example: 1.050 – 1.012 = 0.038/0.0075 = 5% ABV.

Ale
Ales are beers fermented with top fermenting yeast. Ales typically are fermented at warmer temperatures than lagers, and are often served warmer. The term ale is sometimes incorrectly associated with alcoholic strength.

Alpha Acid
One of two primary naturally occurring soft resins in hops (the other is Beta Acid). Alpha acids are converted during wort boiling to iso-alpha acids, which cause the majority of beer bitterness.

Bottle Conditioning
A process by which beer is naturally carbonated in the bottle as a result of fermentation of additional wort or sugar intentionally added during packaging.

Cold Break
The flocculation of proteins and tannins during wort cooling.

Decoction Mash
The method of removing some of the mash, boiling it, then returning it to the main kettle to boost the mash temperature.

Diacetyl
A volatile compound produced by some yeasts which imparts a caramel, nutty or butterscotch flavor to beer. This compound is acceptable at low levels in several traditional beer styles.

Dimethyl Sulfide (DMS)
At low levels, DMS can impart a favorable sweet aroma in beer. At higher levels DMS can impart a characteristic aroma and taste of cooked vegetables, such as cooked corn or celery. Low levels are acceptable in and characteristic of some Lager beer styles.

Dry Hopping
The addition of hops late in the brewing process to increase the hop aroma of a finished beer without significantly affecting its bitterness. Dry hops may be added to the wort in the kettle, whirlpool, hop back, or added to beer during primary or secondary fermentation or even later in the process.

Final Gravity
The specific gravity of a beer as measured when fermentation is complete (when all desired fermentable sugars have been converted to alcohol and carbon dioxide gas). Synonym: Final specific gravity; final SG; finishing gravity; terminal gravity.

Flocculation
The behavior of suspended particles in wort or beer that tend to clump together in large masses and settle out. During brewing, protein and tannin particles will flocculate out of the kettle, coolship or fermenter during hot or cold break. During and at the end of fermentation, yeast cells will flocculate to varying degrees depending on the yeast strain, thereby affecting fermentation as well as filtration of the resulting beer.

HERMS
An acronym for Heat Exchanged Recirculating Mash System, a type of brewing system that many homebrewers use that utilizes a heat exchanger in the Hot Liquor Tank (HLT). The mash water is pumped through this coil, picking up heat from the surrounding water, and returned to the mash lauter tun (MLT).

Hot Break
The flocculation of proteins and tannins during wort boiling.

Hydrometer
A glass instrument used to measure the specific gravity of liquids as compared to water, consisting of a graduated stem resting on a weighted float.

Infusion Mash
The traditional British method of mashing, primarily used in ale brewing. It occurs at a single temperature and is carried out in a combination mash-lauter vessel.

International Bitterness Units (IBU)
The measure of the bittering substances in beer (analytically assessed as milligrams of isomerized alpha acid per liter of beer, in ppm). This measurement depends on the style of beer. Light lagers typically have an IBU rating between 5-10 while big, bitter India Pale Ales can often have an IBU rating between 50 and 70.

Kraeusen
The rocky head of foam which appears on the surface of the wort during fermentation.

Lager
Lagers are any beer that is fermented with bottom-fermenting yeast at colder temperatures. Lagers are most often associated with crisp, clean flavors and are traditionally fermented and served at colder temperatures than ales.

Lautering
The process of separating the sweet wort (pre-boil) from the spent grains in a lauter tun or with other straining apparatus.

Lovibond
A scale used to measure color in grains and sometimes in beer. See also Standard Reference Method.

Mashout
The process of raising the mash (e.g. by adding hot water to it) to a temperature around 75 °C or 170 °F, so as to stop the enzymatic conversion of starch to fermentable sugar and make the mash and wort more fluid.

Mash Lauter Tun
A vessel used in the mashing process to convert the starches in crushed grains into sugars for fermentation. Most mash tuns are insulated to maintain a constant temperature and most have a false bottom and spigot so that the sparging process can be done in the same vessel.

Original Gravity (OG)
The specific gravity of wort before fermentation. A measure of the total amount of solids that are dissolved in the wort as compared to the density of water, which is conventionally given as 1.000 and higher. Synonym: Starting gravity; starting specific gravity; original wort gravity.

Oxidized
Stale, winy flavor or aroma of wet cardboard, paper, rotten pineapple sherry and many other variations.

Pitching
The addition of yeast to the wort once it has cooled down to desirable temperatures.

Priming
The addition of small amounts of fermentable sugars to fermented beer before racking or bottling to induce a renewed fermentation in the bottle or keg and thus carbonate the beer.

RIMS
An acronym for Recirculating Infusion Mash System, a type of brewing system that many homebrewers use. The RIMS system relies on a form of direct heating where the mash water (wort) is pumped through a small tube in which an electric heating element has been installed. The wort is pumped through this tube, past the heating element, and heated to the proper temperature prior to returning to the MLT.

Saccharification
The process of converting starches contained in malt into fermentable sugars

Sparging
A process that brewers conduct during mashing in which spent grains are sprayed with hot water in order to extract the remaining sugars from the husks.

Trub
Wort particles resulting from the precipitation of proteins, hop oils and tannins during the boiling and cooling stages of brewing.

Vorlauf
A German word referring to the process of recirculating wort through the grain bed.

Wort
The bittersweet sugar solution obtained by mashing the malt and boiling in the hops, which becomes beer through fermentation.

Yeast
During the fermentation process, yeast converts the natural malt sugars into alcohol and carbon dioxide gas. Yeast was first viewed under a microscope in 1680 by the Dutch scientist Antonie van Leeuwenhoek; in 1867, Louis Pasteur discovered that yeast cells lack chlorophyll and that they could develop only in an environment containing both nitrogen and carbon.

Zymurgy
The branch of chemistry that deals with fermentation processes, as in brewing.