acrospire. The germinal plant-growth of the barley kernel.
ad-humulone. The third (or sometimes second) most prevalent of the three alpha acids, which, when isomerized during boiling of the wort, provides most of the bittering characteristic that comes from hops.
adjunct. Any unmalted grain or other fermentable ingredient added to the mash.
adjuncts. Sources 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. Introducing 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.
agar (Agar-agar). A non-nitrogenous, gelatinous solidifying agent, more heat-stable than gelatin. A culture medium for microbial analysis.
agglutination. The grouping of cells by adhesion.
airlock. See fermentation lock.
airspace. See ullage.
albumin. Intermediate soluble protein subject to coagulation upon heating. Hydrolyzed to peptides and amino acids by proteolytic enzymes.
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 = .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.
aldehyde. An organic compound that is a precursor to ethanol in a normal beer fermentation via the EMP pathway. In the presence of excess air, this reaction can be reversed, with alcohols being oxidized to very complex, unpleasant-tasting aldehydes, typically papery/cardboardy/sherry notes. These compounds are characterized as oxidized alcohols, with a terminal CHO group.
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.
aleurone layer. The enzyme- and pentosan-bearing layer enveloping, and inseparable from, the malt endosperm.
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 HBU.
alpha acid (a-acid). The principle source of bitterness from hops when isomerized by boiling. These separate but related alpha acids come from the soft alpha resin of the hop.
alpha acid. A soft resin in hop cones. When boiled, alpha acids are converted to iso-alpha-acids.
alt. The German word for old. This is a top-fermenting style of beer that undergoes a cold lagering for maturation.
ambient temperature. The surrounding temperature.
amino acids. The building blocks of proteins. Essential components of wort, required for adequate yeast growth. They are the smallest product of protein cleavage; simple nitrogenous matter.
amylodextrin. From the diastatic reduction of starch; a-limit dextrin; the most complex dextrin from hydrolysis of starch with diastase. Mahogany (red-brown) color reaction with iodine.
amylolysis. The enzymatic reduction of starch to soluble fractions.
amylopectin. Branched starch chain; shell and paste-forming starch. Unable to be entirely saccharified by amylolytic enzymes, a-limit dextrins, or amylodextrins, remain.
amylose. Straight chain of native starch; a-D-glucose (glucose dehydrate) molecules joined by a-(1-4) links. Gives deep blue-black color with iodine.
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.
analyte. A chemical compound that is the target of a particular assay or test system.
anion. An electronegative ion.
apparent attenuation. A simple measure of the extent of fermentation that a wort has undergone in the process of becoming beer. Using gravity units (GU), Balling (B), or Plato (P) units to express gravity, apparent attenuation is equal to the original gravity minus the terminal gravity divided by the original gravity. The result is expressed as a percentage and equals 65% to 80% for most beers.
apparent extract. A term used to indicate the terminal gravity of a beer.
aqueous. Of water.
ash. The residue left behind after all the organic matter of a substance has been incinerated. It consists of mineral matter and serves as a measure of the inorganic salts that were in the original substance.
attemper. To regulate or modify the temperature.
attenuate. Reduction of the extract/density by yeast metabolism.
attenuation. The reduction in the wort’s specific gravity caused by the transformation of sugars into alcohol and carbon-dioxide gas.
autolysis. Yeast death due to shock or nutrient-depleted solutions.
bacteriostatic. Bacteria-inhibiting.
Balling. A saccharometer invented by Carl Joseph Napoleon Balling in 1843, it is a standard for the measurement of the density of solutions. It is calibrated for 63.5 °F (17.5 °C), and graduated in grams per hundred, giving a direct reading of the percentage of extract by weight per 100 grams solution. For example: 10 °B = 10 grams of sugar per 100 grams of wort.
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 the 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 yeasts that have a role in the production of some beers, such as modern lambics and Berliner weisse and historical porters.
brewer’s gravity (SG). See gravity.
BU:GU ratio. The ratio of bitterness units to gravity units 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. 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.
calandria. A shrouded percolator for boiling wort. It can be internal or housed externally and fed by pipes with the use of pumps.
carbonates. Alkaline salts 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) to fermented wort prior to bottling, creating a secondary fermentation in the bottle; or (4) finishing fermentation under pressure.
carboy. A large glass, plastic, or earthenware bottle.
caryophylline. A secondary component of hop oil found in varying proportions in different varieties of hops.
cation. Electropositive ion.
cellulose. A polymer of sugar molecules that plays a structural rather than storage role. The sugars that make up cellulose cannot be liberated by the enzymes found in most plant systems.
chill haze. Haziness caused by protein and tannin during the secondary fermentation.
chill-proof. Cold conditioning to precipitate chill haze.
clarigen finings. Carrageen-based finings.
closed fermentation. Fermentation under closed, anaerobic conditions to minimize risk of contamination and oxidation.
co-humulone. The second (or sometimes third) most prevalent of the three alpha acids, which, when isomerized during boiling of the wort, provide most of the bittering characteristic that comes from hops.
coliform. Waterborne bacteria, often associated with pollution.
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 with 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 °F [13 to 21 °C] rest which 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 concentration, from yeast or Pediococcus bacteria metabolism. Most significantly the butter aroma of diacetyl, a vicinal diketone (VDK). The other significant compound relevant to brewing is 2,3-pentanedione.
dimethyl sulfide (DMS). An important sulfur-carrying compound originating in malt. Adds a crisp, “lager-like” character at low levels, and corn or cabbage flavors at high levels.
disaccharides. 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 to casked beer to add aroma and hop character to the finished beer without adding significant bitterness.
dry malt. Malt extract in powdered form.
EBC (European Brewery Convention). See SRM.
enzymes. Protein-based organic catalysts that affect changes in the compositions of the substances they act upon.
erythrodextrin. Tasteless intermediate dextrin. Large a-limit dextrins. Faint red reaction with iodine.
essential oil. The aromatic volatile compounds from the hop.
ester. A class of organic compounds created from the reaction of an alcohol and an organic acid. These tend to have fruity aromas and are detectable at low concentrations.
esters. “Ethereal salts” such as ethyl acetate; aromatic 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, though 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 esters.
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.
farnescene. A secondary component of hop oil found in varying proportions in different varieties of hops.
fecal bacteria. Coliform bacteria associated with sewage.
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, bentonite, silica gel, or polyvinyl pyrrolidone.
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, creating clearer or brighter beer.
germination. Sprouting of the barley kernel, to initiate enzyme development and conversion of the malt.
glucophilic. An organism that thrives on glucose.
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 ml water weighs 1 g, 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.
hemocytometer. A device used for counting blood cells (or brewers’ yeast) under a microscope.
hexose. Sugar molecules of six carbon atoms. Includes glucose, fructose, lactose, mannose, and galactose.
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 AAU.
homofermentive. Organisms that metabolize only one specific carbon source.
hop pellets. Finely powdered 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.
humulene. A primary component of the essential oil of the hop cone. Although rarely found in beer in this native form, it is processed into a number of flavor-active compounds that are significant in beer. The quantity of humulene found in a hop varies by variety, year, and growing region.
humulone. The most prevalent of the three alpha acids, which, when isomerized during boiling of the wort, provides most of the bittering characteristic that comes from 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). This is 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 which 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-zero temperatures in order to precipitate yeast cells and proteins and improve taste.
lauter. The clear liquid of the mash after saccharification. 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.
lipids. Fatlike substances, especially triacylglycerols and fatty acids. Negatively affect a beer’s ability to form a foam head. Cause soapy flavors; when oxidized, contribute stale flavors.
liquefaction. The process by which alpha-amylase enzymes degrade soluble starch into dextrin.
malt. Barley that has been steeped in water, germinated, 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, and 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.
melanoidins. Color-producing compounds produced through a long series of chemical reactions that begin with the combination of a sugar and an amino acid.
methylene blue. A stain used to test the viability (ability to reproduce) of a yeast cell.
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 there is and the lower the protein level.
mole. A unit of measure for chemical compounds. The amount of a substance that has a weight in grams numerically equal to the molecular weight of the substance. Also gram-molecular weight.
myrcene. A primary component of the essential oil of the hop cone. Although rarely found in beer in this native form, it is processed into a number of flavor-active compounds that are significant in beer. The quantity of myrcene found in a hop varies by variety, year, and growing region.
original gravity. 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, oftentimes causing off-flavors, as with oxidized alcohols to form aldehydes. 2. A reaction in which the atoms in an element lose electrons and its 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 when using the parti-gyle system. 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.
pectin. Vegetable/fruit substance. A chain of galacturonic acid that becomes gelatinous in the presence of sugars and acids.
pentosan. Pentose-based complex carbohydrates, especially gums.
pentose. Sugar molecules of five carbon atoms. Monosaccharides.
peptonizing. The action of proteolytic enzymes upon protein, successively yielding albumin/proteoses, peptides, and amino acids.
pH. A measure of acidity or alkalinity of a solution, usually on a scale of one to fourteen, where seven is neutral.
phenols. Aromatic hydroxyl precursors of tannins/polyphenols. “Phenolic” in beer describes medicinal flavors from tannins, bacterial growth, cleaning compounds, or plastics.
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 °F (20 °C). 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, polypeptides from peptides.
polyphenol. Complexes of phenolic compounds involved in chill haze formation and oxidative staling.
polysaccharides. Carbohydrate complexes, 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 may 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 create carbonation.
protein. 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, etc.).
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 beers that have undergone a secondary fermentation in the container from which they are served and that are served without the application of carbon dioxide.
resin. Noncrystalline (amorphous) plant excretions.
rest. Mash rest. Holding the mash at a specific temperature to induce certain enzymatic changes.
ropy fermentation. Viscous gelatinous blobs, or “rope,” from bacterial contamination.
rousing. Creating turbulence by agitation; mixing.
ruh beer. The nearly fermented beer, ready for lagering. Cold secondary fermentation.
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. A measure of a substance’s density as compared to that of water, which is given the value of 1.000 at 39.2 °F (4 °C). 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.
SRM (Standard Reference Method) and EBC (European Brewery Convention). 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, starch is 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.
steeping. The initial processing step in malting, where the raw barley is soaked in water and periodically aerated to induce germination.
strike temperature. The initial (target) temperature of the water when the malted barley is added to it to create the mash.
substratum. The substance in or on which an organism grows.
tannin. Astringent polyphenolic compounds, capable of colliding with proteins and either precipitating or forming haze fractions. Oxidized polyphenols form color compounds relevant in beer. Also see polyphenol.
terminal extract. The density of the fully fermented beer.
titration. Measurement of a substance in solution by the addition of a standard disclosing solution to initiate an indicative color change.
trisaccharide. A sugar composed of three monosaccharides joined by the removal of water molecules.
trub. Flocks of haze-forming particles resulting from the precipitation of proteins, hop oils, and tannins during 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, especially 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 = .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.