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Food Microbiology > Beer, Wine, Cider > Flashcards

Beer, Wine, Cider Flashcards

1
Q

What is the composition of beer?

A

Water, alcohol, CO2, various flavor compounds (carbs, proteins, minerals, aromatic compounds)

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2
Q

The process of beer production is known as: ___. The main microorganism involved is: ____.

A

brewing

yeast

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3
Q

How is density of the developing beer determined? Why is this important?

A

Density = ORIGINAL GRAVITY (specific gravity)
determine with hydrometer or refractometer

determine amount of dissolved sugars -> calculate final alcohol content, see how far fermentation has progressed

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4
Q

What is SG?

A

specific gravity: ratio of density in comparison to pure water

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5
Q

A wort with SG value of 1.050 is estimated to produce an alcohol content of ____

A

5%

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6
Q

What is an alternative measurement of density?

A

degrees Plato

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7
Q

What is ABV and how is it calculated?

A

alcohol by volume

(OG - TG) x 131.25

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8
Q

What is “TG?”

A

terminal gravity - gravity at end of ferment

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9
Q

True/False: a refractometer can determine the alcohol quantity based on its refractive properties

A

false; alcohol distorts readings.

refractometer works with sugar (based on refractive properties)

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10
Q

How do you use a hydrometer?

A

put instrument (weighted glass tube) in sample, allow to float -> take reading

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11
Q

True/False: the darker the beer, the more alcohol and bitterness

A

False; not related

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12
Q

____ is responsible for the bitterness in beer, which is measured in ____.

A

isomerized alpha acid

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13
Q

A high attenuation beer will be lower in _____. Why?

A

sugar

fermentation closer to completion

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14
Q

How is apparent attenuation calculated?

A

(OG-TG)/OG

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15
Q

What are the main steps of beer production? (6)

A
  1. Malting
  2. Milling
  3. Mashing
  4. Addition of Hops
  5. Fermentation
  6. Conditioning
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16
Q

What is achieved by the malting step in making beer?

A

Grains are soaked/drained repeatedly -> allowed to germinate
rootlets form
sugars stored in seed are released (made available)

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17
Q

What are the raw ingredients and microbes needed for beer?

A

Grain (barley), hops for flavor, water, yeast

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18
Q

How does moisture content of grains change during malting?

A

grains start <20% moisture

soaking -> 42-46% moisture (start germinating)

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19
Q

Why must there be drainage periods during malting?

A

allow for CO2 to be dispersed among grains -> promotes germination

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20
Q

What occurs during milling? What are the types of mills?

A

grains broken down for easier fermentation (consistent sizes)
wet/dry

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21
Q

What does the mashing step consist of? What does it produce?

A

add brewing water to malt -> produces WORT

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22
Q

When are hops added in beer production?

A

added to wort (boiled) before yeast addition

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23
Q

What are the varieties of hops used, and their purposes?

A 
aroma hops (smell)
alpha hops (taste)
dual purpose hops (both)
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24
Q

What form can hops come in? (4)

A

extract, pellets, fresh, dried

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25
Q

What are the main sugars in wort? (6)

A 
maltose
dextrins
maltotriose
glucose
fructose
sucrose
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26
Q

What are the effects of adding too much vs too little yeast?

A

too little: slow ferment, other microbes may grow

too much: competition between yeast, poor growth

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27
Q

What are the effects of temperature on beer ferment?

A 
too low (<5C): cold shock -> longer lag period, slower 
too high: could kill yeast
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28
Q

a normal lag phase is: ____

A

6-15 hrs

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29
Q

Why is it important to encourage yeast to start growing rapidly at the beginning of beer making?

A

quickly outcompete other microbes, prevent spoilage/pathogens

30
Q

What conditions are necessary to make yeast produce ethanol? Why?

A 
presence of sugar (need substrate)
anaerobic conditions (less sugar uptake in aerobic conditions)
31
Q

Even with unlimited hexoses and anaerobic conditions, why does yeast growth eventually stop? (3)

A

cannot perform cell wall synthesis in anaerobic conditions

levels of ethanol become toxic

cells floculate (clump) and sink

32
Q

During what phase of growth is the most ethanol produced? How long is this period? What else is produced?

A 
exponential phase (last 3-4 days)
CO2, heat
33
Q

Why is cooling needed during the exponential growth phase?

A

heat produced; if temp rises too much, other alcohols (propanol, isobutyl alcohol, etc) are produced -> off flavor

34
Q

what is “green beer?”

A

beer that has just completed fermentation

35
Q

What is conditioning?

A

chill to 9-11C, store in tanks for period of time

36
Q

What are the 5 purposes of conditioning?

A
  1. flavor maturation (allow yeast to PURGE/remove bad compounds)
  2. clarification (let yeast cells settle, so can remove)
  3. stabilization (add stabilizer to prevent chem rxn forming precipitates)
  4. carbonation (add CO2 in headspace, dissolves in at low temp)
  5. minimize oxygen (keep in anaerobic tanks, add antioxidants)
37
Q

What compounds can be removed by purging with yeast?

A

H2S, acetaldehyde, diacetyl

38
Q

Is there danger if bacterial spores are present in the final beer product?

A

Not likely; beer is low in nutrients so unlikely to germinate

39
Q

True/False: pathogen contamination of beer is not a concern

A

true

40
Q

Why is wort prone to spoilage?

A

nutrient rich, oxygenated

41
Q

A low alcohol beer stored anaerobically has a strong rotten egg smell. What occurred?

A

contaminated with Megasphaera (anaerobic, grow at low ABV)

42
Q

What microbe infects cask-conditioned beers? what does it cause?

A

zymomonas

cause “cider sickness” - secondary ferment -> frothing, less sweet, off odors

43
Q

What microbe contaminates beer and produces propionic acid, other organic acids, and H sulfide?

A

pectinatus

44
Q

What do LAB cause in beer?

A

spoilage: turbidity, acid, off flavor and odor

45
Q

What microbes may contaminate exposed beer (aerobic)?

A

AAB

46
Q

A beer stored without a lid is cloudy and has a slimy layer. what has occurred?

A

AAB contamination (converts ethanol to acetic acid)

47
Q

What is the base ingredient for wine?

A

grapes

can use other fruit, but need to add water/sugar

48
Q

Why are wines from certain years (vintages) considered higher quality?

A

climate affects grape crop quality -> affect final wine composition

49
Q

What are the 2 main sugars present in grape must?

A

glucose, fructose

50
Q

How does the process for red wine differ from white wine?

A

maceration and partial ferment (to extract tannins, color) before skins are removed

51
Q

What are the 3 phases of wine fermentation, and their durations?

A
  1. lag phase (few hours)
  2. growth phase (24-36 hours)
  3. stationary phase (long period)
52
Q

True/False: in the stationary phase, yeast activity stops

A

False; activity slows, but remains active until 90% sugars depleted

53
Q

What is the purpose of CO2 as a substrate in wine?

A

used to make metabolites/aroma compounds

54
Q

What is different about the process of making Chardonnay wine?

A

secondary ferment step to develop taste

MALOLACTIC FERMENTATION

55
Q

What organisms are used for malolactic fermentation? What process occurs?

A 
Oenococcus onesie (some other LAB can also do it)
convert L-MALIC ACID -> L-LACTIC ACID + CO2
56
Q

What organisms are initially present on grapes? Why must they be removed?

A

wild yeasts

remove so S. cerevisiae can dominate, prevent spoilage

57
Q

What is important to prevent spoilage in winemaking?

A
  1. sulfiting (kill wild yeast)
  2. anaerobic conditions (prevent spoilage aerobes)
  3. grow yeast quickly to exhaust sugars
58
Q

True/false: the sulfiting process removes all yeast except S. cerevisiae

A

False; certain other species also resistant, will survive and participate in ferment

59
Q

What is “sulfiting?”

A

addition of sulfur dioxide as an antimicrobial (or antioxidant)

60
Q

What property makes sulfur dioxide lethal to most microbes? (2)

A

sulfur dioxide bound to water will easily enter cell -> pH driven dissociation -> bisulfite, sulfite (affect gradient)

react with cell molecules: rupture disulfide bridges, react with cofactors, deaminate cytosine (fatal mutations)

61
Q

What mutation (unique to wine yeast) gives it sulfite resistance?

A

chromosomal mutation

SSU1-R1 and SSU1-R2 (sulfite efflux pumps) expressed at high levels

62
Q

How do SSU1-R1 and SSU1-R2 differ?

A

SSU1-R2 has increased expression in first few hours of wine ferment

63
Q

What do campden tablets consist of? What are they used for? (3)

A

Na metabisulfute

Sterilize, remove free Cl, act as antioxidant

64
Q

What is used to stabilize wine by halting yeast? When is it added?

A

K sorbate

add at end

65
Q

What should you do if you somehow add ALL your campden tablets in?

A

THROW THAT SHIT OUT MF

66
Q

What is a “stuck fermentation?”

What are some possible causes? (6)

A

fermentation stops prematurely

nutrient deficiency
inhibitory substances (acid, too much sulfur dioxide)
killer toxins (from competing yeasts)
low pH (<3)
pesticides
temperature
67
Q

True/False: LAB growth in wine should always be avoided

A

False

usually considered spoilage, but LAB can also be used for malolactic ferment in some wine types

68
Q

What is the notable compound produced by LAB in wine? What is the resulting profile?

A

diacetyl
small amount -> nutty aroma (good)
higher amount -> spoilage

69
Q

What has occurred if your wine tastes more acidic than alcoholic?

A

spoilage caused by AAB

70
Q

How is balsamic vinegar of modena produced? (4)

A

cook grape must
yeast convert sugar -> ethanol
oxidize to acetic acid by AAB
12 yrs aging (becomes concentrated and complex)

71
Q

What can beer, cider, and wine be further fermented into?

A

vinegar (with AAB)

malt, cider, and wine vinegars

Food Microbiology (21 decks)

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