Glossary

FACTS

• responsible for lowering pH during fermentation

EXAMPLES

• acetic (vinegar)
• butyric, isobutyric (butter)
• capric, caproic, caprylic (soap, sweat, goat)
• citric (tart)
• formic
• lactic
• malic
• oxalic
• oleic, linoleic
• propionic
• pyruvic
• valeric

CAUSES

• wort trub
• hop-staling
• by-products of yeast carbohydrate metabolism

EFFECTS

• some end as fatty acids responsible for off-flavors

% ALCOHOL BY WEIGHT

• 42 (°P original gravity – °P final gravity)

% ALCOHOL BY VOLUME

• (alcohol by weight x specific gravity of beer) / 0.791

FACTS

• high flavor and staling potential

EXAMPLES

• trans-2-nonenal
• furfural

CAUSES

• formed in Browning reactions during malting and mashing
• can increase or decrease during fermentation

EFFECTS

• responsible for “stale”, “paper” and “cardboard” flavors

EXPECTED VALUES

• dark ale = 68-75%
• lager = 78-86%
• pilsner = 80-85%
• light = 100%

% APPARENT ATTENUATION

• °Plato of original wort – °Plato of final wort / °Plato of original wort

FACTS

• condensation product of an alcohol and an acid

EXAMPLES

• isoamyl acetate (banana)
• ethyl acetate (apple)

CAUSES

• produced during yeast lipid synthesis
• yeast strains differ in their production
• high pitch rate – low levels
• high fermentation temperature – high levels
• high aeration – low levels
• high gravity – low levels
• high pressure – low levels
• high fatty acid content – low levels

EFFECTS

• “fruit” flavors

FACTS

• produced by all yeasts and some bacteria during amino acid synthesis
• reduced to a less-flavorful compound (2,3-butanediol) by yeast during conditioning

CAUSES OF HIGH LEVELS

• underpitching
• highly-flocculant yeast strain
• inadequate diacetyl rest
• bacterial contamination
• high petite-mutant population

EFFECTS OF HIGH LEVELS

• “butter” flavor
• slick mouth-feel

FACTS

• condensation product of an alcohol and an acid

EXAMPLES

• isoamyl acetate (banana)
• ethyl acetate (apple)

CAUSES

• produced during yeast lipid synthesis
• yeast strains differ in their production
• high pitch rate – low levels
• high fermentation temperature – high levels
• high aeration – low levels
• high gravity – low levels
• high pressure – low levels
• high fatty acid content – low levels

EFFECTS

• “fruit” flavors

FACTS

• sugars and amino acids react during kilning and boiling to yield pigments
• also known as the Maillard reaction

FACTS

• utilization is a function of yeast genetics
• glucose inhibits the transport of maltose and maltotriose in lager yeasts

SUGARS IN ORDER OF YEAST PREFERENCE

• glucose (diffuses through cell wall)
• fructose (diffuses through cell wall)
• sucrose (converted to glucose and fructose by invertase in cell wall)
• maltose, maltotriose (transported through cell wall, then converted to glucose)

FACTS

• passes through yeast cell wall in solution, not as a gas
• forms bubbles at nucleation sites such as trub particles and cell-wall exteriors
• removes volatile sulfur compounds as bubbles rise to surface
• can be present in super-saturated levels at fermentor bottom

CAUSES OF HIGH WORT LEVELS

• too little trub in wort
• fermentor is under pressure

EFFECTS OF HIGH WORT LEVELS

• decreases ester production
• inhibits yeast growth
• slows rate of fermentation

FACTS

• 40-60 million cell/ml needed in suspension for proper effect

FACTS

• produced by all yeasts and some bacteria during amino acid synthesis
• reduced to a less-flavorful compound (2,3-butanediol) by yeast during conditioning

CAUSES OF HIGH LEVELS

• underpitching
• highly-flocculant yeast strain
• inadequate diacetyl rest
• bacterial contamination
• high petite-mutant population

EFFECTS OF HIGH LEVELS

• “butter” flavor
• slick mouth-feel

CAUSES IN WORT

• excessive build-up of copper
• over-sparging of mash, leaching toxic polyphenol-protein complexes into wort
• high nitrite levels in brewing water (>25ppm)
• insufficient wort aeration
• high levels of unsaturated fatty acids

CAUSES IN SLURRY

• over-aeration of slurry with pure oxygen
• high temperature, insufficient nutrients

FACTS

• condensation product of an alcohol and an acid

EXAMPLES

• isoamyl acetate (banana)
• ethyl acetate (apple)

CAUSES

• produced during yeast lipid synthesis
• yeast strains differ in their production
• high pitch rate – low levels
• high fermentation temperature – high levels
• high aeration – low levels
• high gravity – low levels
• high pressure – low levels
• high fatty acid content – low levels

EFFECTS

• “fruit” flavors

SYMPTOMS

• high carbon dioxide evolution

CAUSES

• large amounts of trub
• wort is too chilled
• uneven temperature profile
• uneven yeast distribution
• over-modified malt
• build-up of beerstone
• excessive wort maltose
• unusual characteristics of yeast

SOLUTIONS

• break up yeast by aerating
• remove more trub from wort

SYMPTOMS

• slow, bubbling fermentation, usually appearing after krausen stage

CAUSES

• degenerated or autolyzed yeast
• poor trub elimination
• sudden temperature increase
• poor cellar ventilation
• presence of nitrites
• highly kilned malts

SOLUTIONS

• pump wort into another fermentor
• add vigorous, roused yeast

SYMPTOMS

• slow or no fermentation

CAUSES

• insufficient wort aeration
• lack of fermentable sugars in wort
• wort pH too high (over 5.5)
• fermentor and wort too cold, causing yeast to flocculate
• yeast lacks enzymes need to ferment maltotriose
• weak or degenerated yeast
• inadequately cured malt
• antifoam agents or trub clogging yeast membrane
• extensively demineralized water
• extremely soft water
• water high in carbonate hardness
• high nitrate level (>25ppm)
• high copper content

SOLUTIONS

• add vigorous, roused yeast
• pump wort into another fermentor
• analyze to determine whether yeast is capable of fermenting wort sugar-profile

ADVANTAGES

• lower energy costs
• maximal use of equipment and space
• improved physical stability from better precipitation of chill haze
• improved flavor stability

DISADVANTAGES

• wort- and hop- efficiencies can be reduced
• increased yeast stress
• 50% or more yeast is needed
• number of yeast generations is reduced
• oxygen levels as high as 10-12pmm are needed
• increased cost of losses
• longer fermentation times
• decreased foam stability
• higher final pH

CAUSES IN WORT

• pH above 5.7
• temperature too close to low end of yeast’s fermentation range
• inadequate aeration (empty bottle/stuck regulator)
• insufficient nutrients (especially zinc)
• contamination

CAUSES IN YEAST SLURRY

• too warm storage conditions (over 34°F/1°C)
• too long storage time (greater than 48 hours if unfed)
• poor viability (less than 95%)
• contamination

GUIDELINES

• warm slurry to upper end of yeast’s fermentation range
• aerate if specific gravity has dropped less than 30% of expected total
• add zinc to wort
• add fresh, healthy yeast

FACTS

• by-product of protein synthesis from keto-acids
• have longer carbon-chain length than ethanol

EXAMPLES

• n-propanol (solvent)
• iso-butanol (solvent)
• 2-phenyl ethanol (medicinal)
• 2-methyl-1-butanol (aromatic)
• 3-methyl-1-butanol (spice)

CAUSES

• affected by wort amino acid composition
• high pitch rate – low levels
• high fermentation temperature – high levels
• high aeration – high levels
• high gravity – low levels
• high pressure – low levels
• high fatty acid content – low levels

EFFECTS

• fullness of flavor at low levels
• unpleasant at high levels

SYMPTOMS

• little or no foam though carbonation levels are adequate

CAUSES

• proteases released by autolyzing yeast
• unclean equipment

SOLUTIONS

• do not store yeast under finished beer
• clean and degrease equipment
• check for leaking pump-lubricant

FACTS

• normally purged during fermentation by carbon dioxide

CAUSES

• reduced from sulfite by yeast
• made by yeast from sulfur-containing amino acids
• produced most during budding
• degenerated pitching yeast
• some wort-spoiling bacteria

EFFECTS

• “rotten-egg” odor

LAG PHASE

• changes in pressure, temperature and nutrients
• biosynthesis of enzymes needed for metabolism
• oxygen rapidly removed from wort for sterol and fatty acid synthesis

LOGRITHMIC PHASE

• fast yeast reproduction
• uptake of nutrients and sugars
• heat is generated
• volatiles are driven off

DECLINING PHASE

• increase in acidity, alcohol and carbon dioxide
• utilization of glycogen and sterol reserves
• reproduction ceases
• flocculation

FACTS

• sugars and amino acids react during kilning and boiling to yield pigments also known as the Maillard reaction.

FACTS

• nitrogen content decreases 30% during fermentation
• large concentration of nitrogen is found in wort amino acids
• yeast assimilates nitrogen from amino acids and small proteins
• yeast will manufacture missing amino acids, yielding off-flavors, like phenylethanol (rose)

AMINO ACIDS IN ORDER OF YEAST PREFERENCE

• threonine
• methionine
• isoleucine, leucine
• valine
• tyrosine
• tryptophan
• phenylalanine

TEMPERATURE, °C : SATURATION, mg/l

• 5 : 10
• 6 : 9
• 10 : 8
• 15 : 7

FACTS

• more soluble at lower temperatures
• usually completely taken up within 2 hours of pitch

CAUSES

• yeast enzymes require oxygen to synthesize membrane building-blocks

EFFECTS

• deficiency restricts yeast growth
• deficiency reduces yeast viability
• deficiency impedes complete fermentation
• deficiency alters beer flavor

FACTS

• occurs very rapidly over the first 48 hours of fermentation
• usually spans at least 1 pH unit over fermentation period
• optimal pH for yeast is pH 4.0

CAUSES

• affected by any factor that affects yeast growth
• due 10% to formation of carbon dioxide
• due 20% to formation of organic acids (lactic, succinic, oxalic)
• due 40% to absorption of alkaline substances such as phosphates and amino acids

EFFECTS

• extreme drop produces a less mellow, more astringent, drier-tasting beer

EXAMPLES

• 4-vinyl-guiacol (clove)
• 4-ethyl-guiacol (nutmeg)

CAUSES

• malt and hops
• weiss yeast conversion of ferulic acid

EFFECTS

• “spice” flavors

PRESSURE, HIGH (high fermentation pressure):

CAUSES

• exceedingly tall fermentors
• obstructed blow-off

EFFECTS

• increases FAN in resulting beer
• increases vicinal diketones and diacetyl
• increases acetaldehyde
• decreases yeast growth
• decreases ethyl acetate
• decreases fusel alcohols

FACTS

• specific gravity uses pure water as a reference
• wort contains fermentable sugars which raise the specific gravity

CAUSES OF DROP IN

• yeast metabolize sugars
• soluble substances are used by yeast
• alcohol, which is less dense than water, increases
• carbon dioxide is produced

FACTS

• very low flavor threshold

EXAMPLES

• DMS
• hydrogen sulfide
• sulfite
• thiols

CAUSES

• malt, hops and yeast metabolism
• stressed or autolyzing yeast

EFFECTS

• low levels impart fullness
• high levels are very unpleasant

FACTS

• an intermediate in the synthesis of sulfur-containing amino acids

CAUSES

• derived from wort sulfate
• reduced to sulfite by yeast
• factors which retard yeast growth will increase levels

EFFECTS

• complexing with acetaldehyde leads to early staling

FACTS

• fermentation is an exothermic, biochemical reaction
• every kg of extract fermented produces 140kcal of heat

CAUSES OF LOW TEMPERATURES

• over-zealous wort-cooling
• cold ambient temperatures

EFFECTS OF LOW TEMPERATURES

• increases fermentation time
• encourages yeast to flocculate
• ale yeasts produce more sulfur compounds

CAUSES OF HIGH TEMPERATURES

• inefficient or malfunctioning glycol system

EFFECTS OF HIGH TEMPERATURES

• decreases fermentation time
• decreases acetaldehyde
• increases fermentation by-products
• increases ethyl acetate
• increases fusel alcohols

ALES

• between 15-20°C / 60-70°F

LAGERS

• between 8-13°C / 45-55°F

FACTS

• levels may decrease during storage

EXAMPLES

• methanethiol
• methylmercaptan
• methylthioacetate

CAUSES

• related to yeast amino acid synthesis

EFFECTS

• “young” flavor and aroma
• “light-struck” character if exposed to ultraviolet light

FACTS

• precipitates chill haze proteins
• encourages yeast flocculation

GUIDELINES

• do not exceed drop rate of 20°F / 10°C per hour

LAG PHASE

• changes in pressure, temperature and nutrients
• biosynthesis of enzymes needed for metabolism
• oxygen rapidly removed from wort for sterol and fatty acid synthesis

LOGRITHMIC PHASE

• fast yeast reproduction
• uptake of nutrients and sugars
• heat is generated
• volatiles are driven off

DECLINING PHASE

• increase in acidity, alcohol and carbon dioxide
• utilization of glycogen and sterol reserves
• reproduction ceases
• flocculation

FACTS

• optimal wort level is 0.25ppm

EFFECTS

• high levels lead to higher ester production
• high levels encourage yeast flocculation