adjunct. 1. Any unmalted grain or other fermentable ingredient added to the mash. 2. A source of fermentable extract other than malted barley. Principally corn, rice, wheat, unmalted barley, and glucose (dextrose).
aerate. To force atmospheric air or oxygen into solution. To introduce air to the wort at various stages of the brewing process.
aeration. The action of introducing air to the wort at various stages of the brewing process.
aerobic. In the presence of or requiring oxygen.
airlock. See fermentation lock.
alcohol by volume (ABV). The percentage of volume of alcohol per volume of beer. To calculate the approximate volumetric alcohol content, subtract the final gravity from the original gravity and divide the result by 75. For example: 1.050 – 1.012 = 0.038 / 0.0075 = 5% ABV.
alcohol by weight (ABW). The percentage weight of alcohol per volume of beer. For example, 3.2% alcohol by weight = 3.2 grams of alcohol per 100 centiliters of beer. Alcohol by weight can be converted to alcohol by volume by multiplying by 0.795.
ale. 1. Historically, an unhopped malt beverage. 2. Now, a generic term for hopped beers produced by top fermentation, as opposed to lagers, which are produced by bottom fermentation.
all-extract beer. A beer made with only malt extract as opposed to one made from barley or a combination of malt extract and barley.
all-grain beer. A beer made with only malted barley as opposed to one made from malt extract or from malt extract and malted barley.
alpha acid unit (AAU). The number of AAUs in a hop addition is equal to the weight of the addition in ounces times the alpha acid percentage. Thus, 1 ounce of 5% alpha acid hops contain 5 AAUs. AAU is the same as homebrewers bittering units (HBU).
alpha acid (a-acid). The principal source of bitterness from hops when isomerized by boiling. These separate but related alpha acids come from the soft alpha resin of the hop. (When boiled, alpha acids are converted to iso-alpha-acids.)
ambient temperature. The surrounding temperature.
anaerobic. Conditions under which there is not enough oxygen for respiratory metabolic function. Anaerobic microorganisms are those that can function without the presence of free molecular oxygen.
apparent attenuation. A simple measure of the extent of fermentation that a wort has undergone in the process of becoming beer. When gravity units (GU), Balling (B) units, or Plato (P) units are used to express gravity, apparent attenuation is equal to the original gravity (OG) minus the terminal gravity divided by the OG. The result is expressed as a percentage and equals 65 to 80% for most beers.
apparent extract. The terminal gravity of a beer.
aqueous. Of water.
attemperate. To regulate or modify the temperature.
attenuate. To reduce the extract/density by yeast metabolism.
attenuation. The reduction in the wort’s specific gravity caused by the transformation of sugars into ethanol and carbon dioxide gas.
autolysis. Yeast death due to shock or nutrient-depleted solutions.
Balling. A saccharometer invented by Carl Joseph Napoleon Balling in 1843. A standard for the measurement of the density of solutions. It is calibrated for 63.5 ºF (17.5 ºC) and graduated in grams per 100, giving a direct reading of the percentage of extract by weight per 100 grams solution. For example, 10 degrees Balling (°B) 10 grams of cane sugar per 100 grams of solution.
beerstone. Brownish gray mineral-like deposits left on fermentation equipment. Composed of calcium oxalate and organic residues.
blow-by (blow-off). A single-stage homebrewing fermentation method in which a plastic tube is fitted into the mouth of a carboy, with its other end submerged in a pail of sterile water. Unwanted residues and carbon dioxide are expelled through the tube, while air is prevented from coming into contact with the fermenting beer, thus avoiding contamination.
body. A qualitative indicator of the fullness or mouthfeel of a beer. Related to the proportion of unfermentable long-chain sugars or dextrins present in the beer.
Brettanomyces. A genus of yeast that has a role in the production of some beers, such as modern lambics, Berliner weisse, and historical porters.
brewer’s gravity (SG). See gravity.
BU:GU ratio. The ratio of bitterness units (BU) to gravity units (GU) for a specific beer or group of beers. International bitterness units (IBU) are used for bitterness, and gravity units (GU) are used for the gravity component. GU = original gravity – 1 ¥ 1,000. For most beers and beer styles, the resulting ratio has a value between 0.3 and 1.0.
buffer. A substance capable of resisting changes in the pH of a solution.
carbonate. An alkaline salt whose anions are derived from carbonic acid.
carbonation. The process of introducing carbon dioxide gas into a liquid by (1) injecting the finished beer with carbon dioxide; (2) adding young fermenting beer to finished beer for a renewed fermentation (kraeusening); (3) priming (adding sugar or wort to) fermented wort prior to bottling, thereby creating a secondary fermentation in the bottle; or (4) finishing fermentation under pressure.
carboy. A large glass, plastic, or earthenware bottle.
chill haze. Haziness caused by protein and tannin during the secondary fermentation.
chill-proof. Cold conditioning to precipitate chill haze.
closed fermentation. Fermentation under closed, anaerobic conditions to minimize risk of contamination and oxidation.
colloid. A gelatinous substance in solution.
decoction. Boiling the part of the mash that is boiled.
density. The measurement of the weight of a solution, as compared to the weight of an equal volume of pure water.
dextrin. Soluble polysaccharide fraction from hydrolysis of starch by heat, acid, or enzyme.
diacetyl. See diketone.
diacetyl rest. A warm—55 to 70 ºF (13 to 21 ºC)—rest that occurs during fermentation. During the diacetyl rest, yeast metabolize diacetyl and other byproducts of fermentation.
diastase. Starch-reducing enzymes. Usually alpha- and beta-amylase, but also limit dextrinase and a-glucosidase (maltase).
diastatic malt extract. A type of malt extract containing the diastatic enzymes naturally found in malt and needed for conversion of starch into sugar. This type of extract is sometimes used in recipes that contain grain adjuncts such as corn or rice.
diketone. A class of aromatic, volatile compounds perceivable in minute concentrations, from yeast or Pediococcus bacteria metabolism—most significantly, the butter and butterscotch aroma of diacetyl, a vicinal diketone (VDK). The other significant compound relevant to brewing is 2,3-pentanedione.
disaccharide. Sugar group. Two monosaccharide molecules joined by the removal of a water molecule.
dry hopping. The addition of hops to the primary fermenter, the secondary fermenter, or casked beer to add aroma and hop character to the finished beer without adding significant bitterness.
dry malt. Malt extract in powdered form.
European Brewery Convention (EBC). See SRM.
enzyme. A protein-based organic catalyst that effects changes in the compositions of the substances on which they act.
essential oil. The aromatic volatile compounds from the hop.
esters. Compounds from fermentation composed of an acid and an alcohol, such as the “banana” ester. Formed by yeast enzymes from an alcohol and an acid. Associated with ale and high-temperature fermentations, esters also arise to some extent with pure lager yeast cultures, although more so with low wort oxygenation, high initial fermentation temperatures, and high-gravity wort. Top-fermenting yeast strains are prized for their ability to produce particular mixes of aromatic esters. Tends to have fruity aromas and be detectable at low concentrations.
extract. The amount of dissolved materials in the wort after mashing and lautering malted barley and/or malt adjuncts such as corn and rice.
extraction. Drawing out the soluble essence of the malt or hops.
fermentation lock. A one-way valve that allows carbon dioxide gas to escape from the fermenter while excluding contaminants.
final specific gravity. The specific gravity of a beer when fermentation is complete.
fining. (n.) A clarifying agent. (v.) The process of adding clarifying agents to beer during secondary fermentation to precipitate suspended matter. Examples of clarifying agents are isinglass, gelatin, and bentonite.
flocculation. The tendency of yeast to clump together at the end of fermentation. The greater the tendency for the yeast to flocculate, the faster it will drop out of the solution, thereby creating clearer or brighter beer.
gravity (SG). Specific gravity as expressed by brewers. Specific gravity 1.046 is expressed as 1046. Density of a solution as compared to water. Expressed in grams per milliliter (1 milliliter water weighs 1 gram, hence sp. gr. 1.000 = SG 1000; sp. gr. 1.046 = SG 1046).
gravity units (GU). A form of expressing specific gravity in formulas as a whole number. It is equal to the significant digits to the right of the decimal point (1.055 SG becomes 55 GU, and 1.108 SG becomes 108 GU).
green malt. Malt that has been steeped and germinated and is ready for kilning.
gruit. A mixture of spices and herbs used to bitter and flavor ales before the acceptance of hops as a bittering and flavoring agent.
homebrewers bittering units (HBU). A formula adopted by the American Homebrewers Association to measure bitterness of beer. Example: 1.5 ounces of hops at 10% alpha acid for 5 gallons: 1.5 × 10 = 15 HBU per 5 gallons. Same as alpha acid unit (AAU).
hop pellets. Hop cones compressed into tablets. Hop pellets are 20 to 30% more bitter by weight than the same hop variety in loose form. Hop pellets are less subject to alpha acid losses than are whole hops.
hydrolysis. Decomposition of matter into soluble fractions by either acids or enzymes in water.
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.
hydroxide. A compound, usually alkaline, containing the OH (hydroxyl) group.
inoculate. The introduction of a microbe into surroundings capable of supporting its growth.
international bitterness unit (IBU). A standard unit that measures the concentration of iso-alpha-acids in milligrams per liter (parts per million). Most procedures will also measure a small amount of uncharacterized soft resins, so IBUs are generally 5 to 15% higher than iso-alpha-acid concentrations.
isinglass. A gelatinous substance made from the swim bladder of certain fish and added to beer as a fining agent.
isomer (ISO). Organic compounds of identical composition and molecular weight but having a different molecular structure.
kilning. The final stage in the malting of barley that prepares it for use by the brewer. Kilning reduces the moisture contained in the grain to approximately 4% and also roasts the malt to some extent. The degree of roasting affects the flavor and color of the malt as well as of the beer it produces.
kraeusen. (n.) The rocky head of foam that appears on the surface of the wort during fermentation. Also used to describe the period of fermentation characterized by a rich foam head. (v.) To add fermenting wort to fermented beer to induce carbonation through a secondary fermentation.
Lactobacillus. Species of bacteria that ferments wort sugars to produce lactic acid. Although considered undesirable in most breweries and beer styles, it plays a significant role in the production of some beers, such as Berliner weisse and lambics.
lactophilic. An organism that metabolizes lactate more readily than glucose.
lager. (n.) A generic term for any bottom-fermented beer. Lager brewing is now the predominant brewing method worldwide except in Britain, where top-fermented ales dominate. (v.) To store beer at near-freezing temperatures in order to precipitate yeast cells and proteins and improve taste.
lauter. The process of separating the clear liquid from the spent grain and husks.
lauter tun. A vessel in which the mash settles and the grains are removed from the sweet wort through a straining process. It has a false slotted bottom and spigot.
liquefaction. The process by which alpha-amylase enzymes degrade soluble starch into dextrin.
malt. Barley that has been steeped in water, germinated, and then dried in kilns. This process converts insoluble starches to soluble substances and sugars.
malt extract. A thick syrup or dry powder prepared from malt.
maltose. A disaccharide composed of two glucose molecules. The primary sugar obtained by diastatic hydrolysis of starch. One-third the sweetness of sucrose.
mashing. Mixing ground malt with water to extract the fermentables, degrade haze-forming proteins, and convert grain starches to fermentable sugars and nonfermentable carbohydrates.
melanoidin. A color-producing compound produced through a long series of chemical reactions that begin with the combination of a sugar and an amino acid.
modification. 1. The physical and chemical changes that occur in barley during malting, where complex molecules are broken down to simpler, soluble molecules. 2. The degree to which malt has undergone these changes, as determined by the growth of the acrospire. The greater the degree of modification, the more readily available starch is and the lower the protein level is.
original gravity (OG). The specific gravity of wort previous to fermentation. A measure of the total amount of dissolved solids in wort.
oxidation. 1. The combining of oxygen with other molecules, often causing off-flavors, as with oxidized alcohols, to form aldehydes. 2. A reaction in which the atoms in an element lose electrons and the element’s valence is correspondingly increased (oxidation-reduction reaction).
parti-gyle. An arcane system of brewing in which the first runnings of wort are taken to make a high-gravity beer and the grain is then remashed to create another brew. This can be done yet again to make a third brew, all from the same grains. There is usually no sparging involved. With the advent of more sophisticated equipment that allowed lautering and sparging, the parti-gyle system of brewing lost favor around the end of the nineteenth century.
pH. A measure of acidity or alkalinity of a solution, on a scale of 1 to 14, where 7 is neutral.
phosphate. A salt or ester of phosphoric acid.
pitching. Inoculating sterile wort with a vigorous yeast culture.
Plato, degrees. Commercial brewers’ standard for the measurement of the density of solutions, expressed as the equivalent weight of cane sugar in solution (calibrated on grams of sucrose per 100 grams of solution). Like degrees Balling, but Plato’s computations are more exact.
Plato saccharometer. A saccharometer that expresses specific gravity as extract weight in a 100-gram solution at 68 ºF (20 ºC). A revised, more accurate version of Balling, developed by Dr. Plato.
polymer. A compound molecule formed by the joining of many smaller identical units. For example, polyphenols from phenols and polypeptides from peptides.
polysaccharide. A carbohydrate complex, able to be reduced to monosaccharides by hydrolysis.
ppm. Parts per million. Equal to milligrams per liter (mg/l). The measurement of particles of matter in solution.
precipitation. Separation of suspended matter by sedimentation.
precursor. The starting materials or inputs for a chemical reaction.
primary fermentation. The first stage of fermentation, during which most fermentable sugars are converted to ethyl alcohol and carbon dioxide.
priming. The act of adding priming sugar to a still (or flat) beer so that it can develop carbonation.
priming solution. A solution of sugar in water added to aged beer at bottling to induce fermentation (bottle conditioning).
priming sugar. A small amount of corn, malt, or cane sugar added to bulk beer prior to racking or at bottling to induce a new fermentation and to create carbonation.
protein. A generally amorphous and colloidal complex amino acid containing about 16% nitrogen with carbon, hydrogen, oxygen, and possibly sulfur, phosphorous, and iron. True protein has a molecular weight of 17,000 to 150,000+. In beer, protein will have been largely decomposed to a molecular weight of 5,000 to 12,000 (albumin or proteoses), 400 to 1,500 (peptides), or amino acids. Protein as a haze fraction ranges from molecular weight 10,000 to 100,000 (average 30,000) and as the stabilizing component of foam, from 12,000 to 20,000.
proteolysis. The reduction of protein by proteolytic enzymes to fractions.
racking. The process of transferring beer from one container to another, especially into the final package (bottles, kegs, and so on).
reagent. A substance involved in a reaction that identifies the strength of the substance being measured.
real ale. A style of beer found primarily in England, where it has been championed by the consumer rights group called the Campaign for Real Ale (CAMRA). Generally defined as a beer that has undergone a secondary fermentation in the container from which it is served and that is served without the application of carbon dioxide.
resin. Noncrystalline (amorphous) plant excretion.
rest. Mash rest. Holding the mash at a specific temperature to induce certain enzymatic changes.
rousing. Creating turbulence by agitation. Mixing.
runnings. The wort or sweet liquid that is collected during the lautering of the wet mash.
saccharification. The naturally occurring process in which malt starch is converted into fermentable sugars, primarily maltose. Also called mashing, since saccharification occurs during the mash rest.
saccharometer. An instrument that determines the sugar concentration of a solution by measuring the specific gravity.
secondary fermentation. 1. The second, slower stage of fermentation, which, depending on the type of beer, lasts from a few weeks to many months. 2. A fermentation occurring in bottles or casks and initiated by priming or by adding yeast.
sparge. The even distribution or spray of hot water over the saccharified mash to rinse free the extract from the grist.
sparging. Spraying the spent grains in the mash with hot water to retrieve the remaining malt sugar. This is done at the end of the mashing (saccharification) process.
specific gravity (SG). A measure of a substance’s density as compared to that of water, which is given the value of 1.000 at 39.2 ºF (4 ºC). Specific gravity has no accompanying units because it is expressed as a ratio. Specific gravity is the density of a solution in grams per milliliter.
Standard Reference Method (SRM) and European Brewery Convention (EBC). Two different analytical methods of describing color developed by comparing color samples. Degrees SRM, approximately equivalent to degrees Lovibond, are used by the ASBC (American Society of Brewing Chemists), while degrees EBC are European units. The following equations show approximate conversions: (EBC) = 2.65 × (SRM) – 1.2; SRM = 0.377 × (EBC) + 0.46.
starch. A polymer of sugar molecules. The chief form of energy storage for most plants. It is from starch that the relevant sugars for brewing are derived.
starter. A batch of fermenting yeast added to the wort to initiate fermentation.
strike temperature. The initial (target) temperature of the water when the malted barley is added to it to create the mash.
tannin. Astringent polyphenolic compound, capable of colliding with proteins and either precipitating or forming haze fractions. Oxidized polyphenols form color compounds relevant in beer. See also polyphenol.
terminal extract. The density of the fully fermented beer.
trub. Flocks of haze-forming particles resulting from the precipitation of proteins, hop oils, and tannins during the boiling and cooling stages of brewing.
turbidity. Sediment in suspension. Hazy, murky.
ullage. The empty space between a liquid and the top of its container. Also called airspace or headspace.
viscosity. The resistance of a fluid to flow.
volatile. Readily vaporized. Applies especially to esters, essential oils, and higher alcohols.
volume of beer. To calculate the approximate volumetric alcohol content, subtract the terminal gravity from the original gravity and divide the result by 75. For example: 1.050 – 1.012 = 0.038 / 0.75 = 0.05 or 5% ABV.
water hardness. The degree of dissolved minerals in water. Usually expressed in parts per million (ppm) or grains per gallon (gpg).
wort. Mash extract (sweet wort). The hopped sugar solution before pitching, before it is fermented into beer.