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Food Microbio > Wine, Cider, Beer, and Vinegar > Flashcards

Wine, Cider, Beer, and Vinegar Flashcards

1
Q

what is beer?

A

a solution of water, alcohol and carbon dioxide that is flavored by carbohydrates, proteins, minerals, and different aromatic compounds that it acquires from malt, hops, and yeast.

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2
Q

what is brewing?

A

Is the combined process of preparing beverages from the infusion of grains that have undergone sprouting, and subsequent fermentation of the sugary solution produced, by yeast – where a proportion of the carbohydrate is converted to ethanol and carbon dioxide

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3
Q

what is gravity density of the wort?

A

a way of calculating the amount of dissolved substances, largely sugars that will be converted into alcohol. expressed as original gravity

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4
Q

how is gravity calculated?

A

calculated using either a hydrometer or a refractometer

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5
Q

what is a hydrometer?

A

A weighted glass tube with a scale on the inside which stops at the relative density of the liquid being measured

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6
Q

what is a refractometer?

A

Measures the original gravity only, based on the refractive properties of sugar. Alcohol distorts the readings

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7
Q

what is terminal gravity?

A

how much gravity is left after the fermentation is finished and can be used to calculate the alcohol content of the finished beer (or wine, or cider

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8
Q

what is the alcohol by volume and how do you calculate it?

A

The percentage of ethanol in the finished beer

ABV = (OG - TG) * 131.25

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9
Q

color of a beer

A

The value of lightness/ darkness and red/ yellowness of a beer. Light/ dark measurements are acquired by measuring the beer in a spectrophotometer. Tristimulus are used to assess colour.

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10
Q

bitterness of a beer

A

Is the level of bitterness you taste when you drink beer. It is measured in bitterness units (BU) which relates to ppm isomerized alpha acid

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11
Q

what is attenuation and how can it be altered?

A

way to measure how complete a fermentation process is.
Apparent Attenuation=(OG-TG)/OG
can be altered by sugar type, mashing method, composition of the wort, or type of yeast.

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12
Q

high apparent attenuation signifies a … beer, while low apparent attenuation signify a … beer

A

dry

sweet

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13
Q

what is malting? what is the aim?

A
  • the process of allowing the grain to germinate (usually by soaking them in water) => controlled germination process
  • The aim of malting is to transform the food reserves in the grain into substrates that are convenient for fermenting in the brewery
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14
Q

describe the malting process

A
  • The moisture content of the grains at the start and during storage shouldn’t be higher than 20%
  • To commence the malting the grains are soaked in water to start germination (8h) (happens when the grains are at 42-46% moisture)
  • The water is not left on the grains there are intermittent periods of drainage (10-14h) when air is blown though
  • CO2 is dispersed and this promotes germination
  • Air is blown through the germinating grain bed, and grains are turned slowing in drums or by automated turning arms
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15
Q

what is milling? what are the 2 types?

A

process that breaks down the malt into smaller more fermentable sizes
- wet and dry milling

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16
Q

what is the makes up beer?

A

water + malt + hops + yeast = beer

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17
Q

what is mashing?

A

process where ground malt is mixed with brewing water, such that a fermentable extract is produced that will support the growth of yeast

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18
Q

what is produced after mashing?

A

wort

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19
Q

what are the three varieties of hops?

A
  • aroma hops
  • alpha hops (flavour)
  • dual purpose hops
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20
Q

what do we do with the produced wort after mashing?

A

it is boiled with hops for a bit over an hour before being cooled down and yeast is added

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21
Q

what is the purpose of adding hops to beer making?

A

it adds bitterness to the beer, but can also add a floral taste or fruity or citrusy flavour or aromas

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22
Q

which yeast is used for the fermentation of beer?

A

Saccharomyces cerevisiae

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23
Q

what causes a “cold-shock” during fermentation

A

if the wort is more than 5C cooler than the yeast. this will result in a prolonged lag period (normally it is 6-15h)

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24
Q

what are fusel alcohols?

A

alcoholsthat contain more than two carbons. (Ethanol is a two carbon atom molecule)

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25
Q

what can cause fusel alcohol?

A

yeast stress can lead to undesirable fusel alcohol production

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26
Q

what is the wort composition?

A
  • maltose (50-60%)
  • dextrin (20-30%)
  • matotriose (15-20%)
  • glucose (10-15%)
  • fructose (1-2%)
  • sucrose (1-2%)
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27
Q

in which environment does yeast grow in?

A

aerobic and anaerobic

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28
Q

… conditions are essential for the production of …. by yeast. What happens in the presence of oxygen?

A

anaerobic
alcohol
sugar up-take is diminished

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29
Q

how long does the beer fermentation last?

A

theoretically, as long as anaerobic conditions are available and there are hexoses in the media

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30
Q

why does the theoretical fermentation process of beer does not actually happen in practice? (3 reasons)

A
  • Budding requires cell wall synthesis which cannot happen in anaerobic conditions, therefore eventually growth must cease
  • Eventually the level of ethanol present becomes toxic to yeast
  • When fermentation slows the yeast cells flocculate and sediment out (which causes growth to slow even further)
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31
Q

explain the beer fermentation process

A

The lag phase is followed by a short phase of exponential growth
During the exponential growth phase the yeast density can increase by four- to six-fold
During exponential growth yeast are at their highest level of utilizing sugars and producing ethanol and carbon dioxide
A considerable amount of heat is also produced, and cooling is usually needed to keep the temperature down to 20-22C
If the temperature gets too high higher (fusel) alcohols (propanol, iso-amyl alcohol, or iso-butyl alcohol) will be produced, and this will impart off-flavours
Exponential growth lasts for 48-60 hours, after which growth is decelerated before the cells reach stationary phase

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32
Q

what are the 3 phases of beer fermentation?

A
  1. lag phase
  2. exponential growth
  3. stationary phase
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33
Q

… cause a fruity flavor, and produced during fermentation. They can create a taste and aroma like pears, roses, bananas or other light fruits. They can also create a solvent-like flavour in very high concentrations

A

Esters

34
Q

how are esters formed in beer?

A

“esterification” of ethanol

35
Q

what happens post beer fermentation?

A

Once a beer has been fermented down to its final gravity, it is chilled to 9-11C
Immediately after the fermentation beer is called ‘green beer’ and must still be conditioned before packaging

36
Q

what are the five considerations during beer conditioning?

A
  1. flavour maturation
  2. clarification
  3. stabilization
  4. carbonation
  5. minimize oxygen
37
Q

what is purging during flavour fermentation?

A

The yeast remove undesirable compounds such as H2S, acetaldehyde, and diacetyl

38
Q

why do we do clarification?

A

Green beer can contain 1 x 10^7 cells per mL. This would block your filter during filtration. Thus, the beer is allowed to settle so that yeast can be removed by sedimentation.

39
Q

why do we use stabilizers during conditioning?

A

To prevent a non-biological precipitate to form during storage. Stabilizers are added to remove the precursors of this precipitate.

40
Q

how do we remove oxygen in green beer?

A

If O2 finds its way back in, antioxidants are added

41
Q

CO2 is more soluble at …. temperatures, so a top pressure of CO2 is maintained in conditioning tanks. (carbonation)

A

reduced

42
Q

… are not an issue with brewing

A

pathogens

43
Q

Both wort and beer are prone to … But why wort in particular?

A

spoilage organisms

particularly wort since it provides a nutrient rich, oxygenated environment

44
Q

why isn’t beer a good growth media for bacteria?

A

because it has a low pH, a good ethanol concentration, and is largely devoid of nutrients

45
Q

certain …. can survive the whole process and make it into canned beer

A

spores

46
Q

which are the anaerobic beer spoilers

A
  • LAB (Pediococcus and Lactobacillus) which cause turbidity, acid notes, and unwanted flavours
  • zymomonas
  • megasphaera
  • pectinatus
47
Q

about zymomonas spoilage microbe

A

Infects cask-conditioned beers resulting in ‘cider sickness’ where there is a secondary fermentation with much frothing, a loss of sweetness, and off-odours due to hydrogen sulfide and acetaldehyde production. Due to failure in the cask-washing regime

48
Q

about Megasphaera spoilage microbe

A

Produces hydrogen sulfide in beer producing “rotten egg” smell. Cannot tolerate more than 2.8% ABV so only affects low alcohol beers.

49
Q

about pectinatus spoilage microbe

A

rapidly converts finished beer into propionic acid, acetic acid, succinic acid, lactic acid, and hydrogen sulfide giving the beer a “rotten egg” smell

50
Q

which are the aerobic beer spoilers?

A

primarily AAB (Acetobacter and Gluconobacter) they will result in the oxidization of ethanol to acetic acid. There will be a “raft” of surface growth in the beer that will lead to generalize turbidity, and the infected beer may have a “ropiness” quality.

51
Q

what is wine

A

an alcoholic beverage made from grapes fermented without the addition of sugars, acids, enzymes, water, or other nutrients

52
Q

what are some wines not made from grapes?

A

sake (rice wine), mead (honey), or fruit wines (plum, cherry, elderberry, strawberry)

53
Q

what should be added to most fruit wines?

A

cane sugar

54
Q

what are superior wines?

A

known as vintages and cannot be blended with other wines

55
Q

what are non-vintage wines?

A

generally blended so that wine-makers can still have an acceptable product even in bad years

56
Q

steps in wine making?

A
  1. sampling
  2. harvest
  3. crushing/pressing
  4. fermentation
  5. blending
  6. stabilizing
  7. aging
  8. filtration
  9. bottling/labelling/dispatch
  10. consumption
57
Q

how does white wine making differ from red wine making?

A

white wine has pre-fermentation treatments; settling and removal of skin before inoculation and red wine has a maceration and partial fermentation step after inoculation

58
Q

what is the typical wine fermentation process?

A

Wine fermentation typically comprises a lag phase which lasts a few hours, a short growth phase (24-36 hr), and a long stationary phase during which most of the sugar is converted into alcohol
During the stationary phase the yeast activity continually decreases, although viability remains around 90% until the sugar is depleted

59
Q

what is the most desirable outcome for wine fermentation?

A

complete degradation of sugars into ethanol, and CO2 to provide metabolites and aroma compounds that positively impact the sensory balance of the wine

60
Q

what is malolactic fermentation import for?

A

chardonnay making

important in the taste development of wine

61
Q

what is the process of malolactic fermentation? which bacteria carries out this reaction?

A

L-malic acid is converted into L-lactic acid and CO2

several LAB but commercial strains of Oenococcus onesie are generally used

62
Q

what are management conditions required to make sure that brewing saccharomyces cerevisiae dominate the fermentation, and other yeast are removed? (3)

A

sulfiting
anaerobic conditions (many spoilage organisms rely on oxidative metabolism )
rapid and complete exhaustion of sugars

63
Q

why is sulfur dioxide added in wine making?

A

to kill natural species and allow wine specific Sc (which are resistant to sulfur dioxide) to carry out the fermentation, but despite the addition of sulfur dioxide several different species of yeast participate in the process

64
Q

why is sulfur dioxide widely used in the food industry as well as in wine making?

A

for its anti oxidative and antimicrobial properties

65
Q

how does sulfur dioxide inhibit the growth of microbes?

A

it ruptures disulfide bridges in proteins, and reactions with cofactors. It can also deaminate cytosine to uracil which increases the likelihood of fatal mutations

66
Q

how did sulfite resistance happen?

A

in wine yeast ONLY there was a reciprocal translocation between chromosome 8 and 16 that resulted in a dominant allele of the sulfite pump (SSU1-R1) that is expressed at much higher levels and confers a very high level of sulfite resistance
there is a second translocation resulting in SSU1-r2 that is increased in expression during the first hours of a wine fermentation

67
Q

what are Campden tablets used for?

A
  • used to sterilize wine, cider, and beer by amateur brewers, since it allows the easy measurement of very small quantities of sodium metabisulfite
  • can also eliminate free chlorine from water solutions
  • used as an antioxidizing agent when transferring wine between containers. The sodium metabisulfite in the Campden tablets traps the oxygen that enters the wine, and prevent it from doing any harm
68
Q

…. must be used to halt the yeast and preserve the wine

A

potassium sorbate

69
Q

what is a significant problem that can arise during wine fermentation? what is that?

A

stuck fermentation, which is when there is a premature cessation of alcohol production in the fermentation

70
Q

what can cause a stuck fermentation?

A
  • Nutrient deficiency (nitrogen, vitamins, or minerals)
  • Inhibitory Substances (acetic acid, lactic acid, excessive sulfur dioxide)
  • Killer toxins (toxins produced by yeasts against other yeasts)
  • pH too low (<3)
  • Pesticides remain on grapes from field
  • Temperature (too low at the beginning, or too high during the ferment)
71
Q

what is one of the most important odor compounds produced by LAB?

A

diacetyl - “buttery” aroma that at low concentrations is described positively as “nutty” but at high concentrations is considered spoilage.

72
Q

which LAB can produce diacetyl?

A

heterofermentative and homofermentative

73
Q

… results in the oxidation of ethanol to acetic acid, and produces odors and off flavors for wine

A

AAB

74
Q

what does vinegary/acidic taste in wine indicate?

A

introduction of AAB - spoiled wine

75
Q

Cider is particularly prone to contamination with … (because present on apple) so it is important to add … at the initial fermentation step

A

acetic acid bacteria

sulfur dioxide

76
Q

steps of cider making

A
  1. chop the apples, squeeze out the juice and send to a settling tank
  2. fermentation of juice at cool temperatures using premium wine-yeast
  3. once all sugar has been transformed by the yeast to cider -> filter out all the yeast
  4. add bubbles
77
Q

what is malt vinegar? how is it made?

A

made from malting barley which results in the conversion of starch to maltose
Maltose is converted to ale and then turned to vinegar which is then aged
(light-brown color)

78
Q

how is cider vinegar made?

A

made with apple juice through a double fermentation with alcohol and acetic acid fermentation in the same barrel by naturally occurring yeasts and acetic acid bacteria.

79
Q

what are the three steps involved in traditional balsamic vinegar making?

A
  • Conversion of sugars to ethanol by yeast
  • Oxidation of acetic acid by acetic acid bacteria
  • At least 12-years of aging by sequential transfer from a larger barrel into a smaller barrel
80
Q

how is rice vinegar made?

A
  • made from fermented rice wine (sake)
  • produced via a static surface fermentation
  • The final acidity is usually about 10%
  • The dominant acetic acid bacteria are usually Acetobacteria
81
Q

what are the three types of rice wine vinegar?

A
  • Komesu is produced from polished rice grains, is pale amber in color, and is used for sushi and seaweed salad
  • Kurosu is produced from unpolished rice grains, is dark black and is used as a table condiment or a healthy drink
  • Kasuzu is produced from sake lees, 210 different acetic acid bacteria were isolated from a traditional fermentation

Food Microbio (11 decks)

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