6) Beer, Wine and Cider Flashcards
define brewing
process of preparing beverages from infusion of grains that have undergone sprouting and fermentation of the sugary solution produced by yeast, where a proportion of the CHO is converted to ethanol and CO2
define gravity
density of the wort or a way of calculating amount of dissolved substances
how is gravity expressed?
- degrees Plato
- original gravity (OG)
- starting gravity (SG)
how is original gravity expressed?
as a ratio of density relative to pure water
how is OG related to the final alcohol content?
the significant digit of OG is an estimation of the final alcohol content
eg. 1.040 wort = 1.040 times as dense as pure water = 4.0% Alcohol By Volume (ABV)
what does ABV stand for? what is it?
ABV = alcohol by volume = percent of ethanol in finished beer
how is gravity measured?
by hydrometer (weight glass tube with scale which stops at relative density of liquid being measured) or refractometer (Based on refractive properties of sugar. Alcohol distorts readings)
describe terminal gravity. What can it be used for?
how much gravity is left after the fermentation is finished. Can be used to calculate the alcohol content of the finished beer/wine/cider
what is the ABV equation?
ABV = (OG - T) * 131.25
what is color measured by in beer?
lightness/darkness is measured by spectrophotometer
color is assessed by Tristimulus
how is bitterness in beer measured?
- in bitterness units (BU) which relates to ppm isomerized alpha acid
what is attenuation?
way of measuring how complete a fermentation process is
what is the eqn of apparent attenuation?
apparent attenuation = (OG - TG) / OG
how can attenuation of a beer be altered?
by sugar type, mashing method, composition of the wort or type of yeast
high apparent attenuation represents what?
a dry beer
low apparent attenuation represents what?
a sweet beer
what is malting?
what is the goal of it?
- the process of allowing the grain to germinate (usually by soaking in water)
- the goal is to transform food reserves in the grain into substrates that are convenient for masking in the brewery
describe the malting process
- before start, moisture content of the grains should not be higher than 20%
- to start, grains are soaked in water to increase to 42-46% moisture for germination
- drainage periods where air is blown through (so that water is not left on grains). This also disperses CO2 to promote germination. As air is blown through germinating grain beds, grains are turned slowly in drums or by automated turning arms
what is milling?
process that breaks down the malt into smaller fermentable sizes
what are 2 types of milling?
wet and dry milling
what is mashing?
what is the result of mashing?
process where ground malt is mixed with brewing water, so that fermentable extract is produce to support growth of yeast
results in wort
what are 3 varieties of hops according to function in brewing?
aroma
alpha
dual purpose
how are hops used in brewing?
- hops are boiled with the wort
- afterwards, yeast is added
what sensory properties does hops add?
bitterness, but also floral, fruity or citrusy aromas
what happens when too much or too little Sc is added to the wort?
Adding too little = very slow initial fermentation
Adding too much = competition between yeast and poor growth
why is temperature imp when adding yeast?
if wort is more than 5C cooler than yeast, it results in cold shock which causes prolonged LAB period
in industrial fermentations, why must microbes start growing as fast as possible?
so growth of other MO is discouraged
what is the composition of wort?
maltose (50-60%) dextrins maltotrios glucose fructose (2%) sucrose (2%)
describe the O2 req needed for yeast growth
can grow anaerobically or aerobically
in anaerobic conditions, yeast produes what?
alcohol
how does O2 presence affect sugar up take of yeast?
decreases
why do yeast fermentations not keep going, even if anaerobic conditions and sugars are present?
b/c budding requires cell wall synthesis, which can’t occur in anaerobic conditions. Eventually, growth must cease
Also, the level of ethanol will eventually become toxic to yeast, which slows the yeast growth
describe the exponential growth phase
- when yeast density increases 4-6x
- highest level of utilizing sugars and producing ethanol + CO2
- high heat production. Requires cooling down to keep temp lower.
- lasts around 48-60 hrs
- after this phase, growth slows
what happens during exponential growth phase when temp is too high?
higher alcohols (pronaol, isoayl alcohol or isobutyl alcohol) will be produced which imparts off flavours
what happens to beer post-fermentation?
what is it called at this stage?
- once beer has been fermented down to its final desired gravity, it is chilled
- called “green beer”
- must be conditioned before packaging
what are 5 considerations during conditioning of beer after fermentation?
- flavour maturation: yeast removes undesirable compounds by the purging process (eg. H2S, acetaldehyde, diacetyl).
- clarification: allows beer to settle so that yeast can be removed by sedimentation
- stabilization: to prevent a non-biological precipitate to form during storage, stabilizers are added to remove precursors of precipitates
- carbonation: CO2 is more soluble at reduced temp, so a top pressure of CO2 is maintained in conditioning tanks
- minimize O2: O2 is low in green beer. If O2 comes back in, antioxidants are added
wort and beer are both prone to _____
spoilage organisms
why is wort especially prone to spoilage?
since it provides a nutrient and O2 rich environment
how can you prevent spoilage of wort and beer?
use process control to prevent contamination
why is beer not a good growth media for bacteria?
since it has low pH and nutrients
how does turbidity and ropiness quality occur in beer?
- aerobic beer spoilers (primary AAB) results in oxidation of ethanol to acetic acid
- causes raft of surface growth in beer
what gives beer a rotten egg smell?
pectinatus and megasphaera
what causes “cider sickness”? how?
Zymomonas
- causes secondary fermentation with frothing, loss of sweetness and off odors due to H2S and acetaldehyde production
vintage vs non-vintage wines?
vintages: superior, can’t be blended with other wines
non-vintage: blended to have acceptable products even in bad years
what are 3 main phases of wine fermentation?
- lag phase: few hours long
- growth phase: 24-36 hours
- stationary phase: longest phase where most sugars are converted to alcohol. Yeast activity decreases although viability is around 90% until sugar is depleted
what is the desirable outcome of wine fermentation?
complete degradation of sugars to ethanol + CO2 to provide metabolites and aroma cmpds
what is malolactic fermentation?
- imp in taste and development of wine
- carried out by LAB or Oenococcus onesie
- L-malic acid –> L-lactic acid + CO2
what conditions are required for Sc to dominate the fermentation by removing other yeasts?
- sulfating
- anaerobic conditions (since many spoilage organisms need oO2)
- rapid and complete exhaustion of sugars
what is the main use of sulfur dioxide in wine?
what are other uses?
to kill natural yeast species to allow wine specific Sc (which are resistant to sulfur dioxide) to dominate the fermentation
other: anti-oxidative and anti-microbial properties
describe the chemical rxn of sulfur dioxide in wine
- SD is dissolved in H2O and enters the cell
- SO2.H2O undergoes rapid pH driven dissociation to bisulfite and sulfite
- SO2 inhibits growth of microbes which ruptures disulfide bridges in proteins, then reacts with cofactors
- deaminates cytosine to uracil which increases possibility of fatal mutations
what is SSU1-R1?
- dominant allele of the sulfite pump
- expressd at higher levels than SSU1
what is the function of Campden tablets?
- to sterilize wine, cider and beer by amateur brewers since it allows easy measurement of small quantities of sodium metabisulfite. Tablets are not used in the industry since they would measure out specific amounts of Na metabisulfite
- eliminates free chlorine from water solutions (ie. when using water from a municipal source)
- antioxidizing agent when transferring wine between containers (since the sodium metabisulfite traps the O2 entering the wine)
what is potassium sorbate used for?
to halt the yeast and preserve the wine
what is a stuck fermentation?
premature cessation of alcohol production in the fermentation
what is a stuck fermentation caused by?
- nutrition deficiency (N, vitamins, minerals)
- inhibitory substances (Acetic acid, lactic acid, excessive sulfur dioxide)
- killer toxins (produced by yeasts against other yeasts)
- pH too low (less than 3)
- pesticides remaining on grapes
- temperature (too low at beginning or too high during ferment)
what is an odor compounds produced by LAB in wine? when is the production of this compound positive or negative?
diacetyl
positive: “butter” aroma at low conc
neg: “nutty” aroma at high conc
what is cider particularly prone to? how can you avoid this?
contamination with AAB
avoid by adding sulfur dioxide at initial fermentation step
describe production of malt vinegar
- malting barley: starch is converted to maltose
- maltose converts to ale
- ale turns to vinegar
- vinegar is aged
describe production of cider vinegar
apple juice is double fermented with alcohol and acetic acid fermentation by yeasts and AAB
describe the production of traditional balsamic vinegar
- sugars are converted to ethanol by yeast
- oxidation of acetic acid by AAB
- at least 12 years of aging
describe the production of rice vinegar
- made from fermented rice wine (sake)
- produced via static surface fermentation
- AAB
what are 3 times of rice wine vinegar?
- Komesu: produced from polished rice grains; pale amber color; used for sushi and seaweed salad
- Kurosu: produced from unpolished rice grains; dar black color; used as a table condiment or healthy drink
- Kasuzu: produced from sake lees; 210 different AAB isolated from a traditional fermentation
