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Food 1130: Traditional alcoholic beverages > Beer part 4: Fermentation > Flashcards

Beer part 4: Fermentation Flashcards

1
Q

What family do yeast belong to?

A

Fungus.

Fungi are the principal decomposers of the ecological kingdom

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2
Q

How many subclasses of yeast are there?

A

3 - one is saccharomycetacea, this contains 4 groups, one of which is saccharomycoidea

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3
Q

What is the genus saccharomyces?

A

Within the saccharomycoidea group, it contains 41 species.

One of the species covers all the brewing and baking yeasts

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4
Q

What are the 3 main yeasts for brewing?

A 
Saccharomyces Cerevisiae (top fermenting ales)
Saccharomyces Pastorianus (bottom fermenting - lagers)
Brettanomyces (wild beers and lambics)
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5
Q

What is yeast responsible for in brewing?

A
  • Metabolic processes that produce ethanol, CO2 (important for 2ndary fermentation)
  • A range of other metabolic by-products that contribute to the flavour and finish of beer
  • There are hundreds of varieties/strains of the brewing species of yeast, different ones have different alcohol tolerances (8-16%)
  • Saccharomyces Cerevisiae has been sequenced and the relationships between the strains have been identified
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6
Q

How does yeast contribute to beer flavour?

A
  • Comes from the esters produced during yeast metabolism

- These esters are the same compounds we smell as fruit ripens

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7
Q

Why does yeast produce smells?

A

To attract fruit flies to help with dispersion of the yeasts into the environment

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8
Q

Why are scientists developing new yeasts?

A

with different flavour characteristics for beverage production such as increased banana and pear flavour for belgian style beers

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9
Q

How do local yeasts affect beverage?

A

Can change flavour of beer and wine - terroir wine regions, wild yeast of lambic beers and kveik yeasts used by home brewers in Norway

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10
Q

What is lager yeast?

A

Saccharomyces Pastorianus (formerly - Carlsbergensis)

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11
Q

When and where was lager yeast isolated?

A

Late 19th century

Carlsberg laboratories - given away freely to other breweries

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12
Q

Where is the genetic sequencing of lager yeast?

A

Early stages

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13
Q

What has recently been discovered regarding lager yeast?

A

It is a hybrid of s.Cerevisiae and S. Eubayanus

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14
Q

Where has S Eubayanus been found?

A

Discovered in the wild in Patagonia in 2011, some evidence suggesting Tibetan origin

  • Also been found in Wisconsin and China
  • Loves the cold
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15
Q

Why do some breweries use 2 yeasts?

A

Because they have complimentary functions e.g. rapidly fermenting strain and one that generates aromatic by-products

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16
Q

What yeast does Heineken use?

A

A proprietary yeast called A yeast - has used the same yeast for more than a century

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17
Q

What yeast did Heinekens H-41 beer use?

A

Wild yeast discovered in 2010 which is a parent of A-yeast - Most likely s-Eubayanus

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18
Q

Why were beers traditionally sour tasting?

A

Wild yeast used to ferment it added sour flavours.

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19
Q

Why is beer generally now not sour?

A

Modern yeast cultures don’t add sour compounds

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20
Q

How are sour flavours intentionally added to beer?

A

Using wild yeast or bacteria

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21
Q

Why is trying to create sour beers risky?

A

As may not create safe/nice tasting beer

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22
Q

Give some examples of sour beers

A

Berliner Weisse - A weak beer flavoured with lactobacillus, generally served with syrups to balance tart flavour
Gose - Flavoured with coriander and salt and sourced with lactobacillus

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23
Q

What is a Lambic style beer?

A

One of the best known sour beers, belgian style beer around 2-8% alcohol and is fermented spontaneously

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24
Q

Why does lambic beer have such a distinct flavour?

A

Exposed to the wild yeast and bacteria of the zenne valley in Belgium

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25
Q

What is the malt blend of a lambic beer?

A

70% barley malt and 30% unmalted wheat

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26
Q

Why are large amounts of hops used in a lambic beer?

A

Because the long inoculation and fermentation times required by wild yeast increase risk of spoilage

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27
Q

What type of hops do modern lambics use and why?

A

Old dry hops that are less hoppy and flavourful but still have antiseptic properties

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28
Q

How are lambic beers drunk/stored?

A

Rarely bottled as is

Draught releases are categorized as old or young depending on fermentation time - can be bracingly sour

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29
Q

What is Gueze?

A

Mix of one and two year old lambics, secondary fermentation happens in bottle

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30
Q

What is a kriek?

A

Lambic fermented in the presence of cherries

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31
Q

What are fruit lambics?

A

Lambic mixed with berries/grapes/stone fruits/ tropical fruits

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32
Q

What sour beers have been released recently?

A

Ones that have no real fruit or secondary fermentation - instead they use souring compounds. The flavour profile of the beer is not as good/complex as a traditional lambic

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33
Q

What are some new strains of yeast that have been identified in relation to wild beers?

A
  • Cultivated from the skins of peaches
  • Cultivated from a San Francisco sourdough starter
  • Cultivated from plum skins
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34
Q

What is rogue ales bear beer?

A

American wild ale, brewed from yeast collected on the beard of the brew master - said to have sharp pineapple flavour

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35
Q

What is mikkeller beer greek brunch weasel

A

An imperial oatmeal stout made with cape cut chon coffee beans collected from civet droppings - pre difested inside the civet

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36
Q

What is the other main flavour compound besides esters?

A

Phenols (spice instead of fruit)

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37
Q

How are yeasts classified in terms of phenols?

A

Phenolic Off Flavour positive of negative (POF+/-)

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38
Q

Generally speaking what are wild yeasts in terms of phenols?

A

POF+

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39
Q

Generally speaking what are commercial yeasts in terms of phenols?

A

POF-

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40
Q

Other than wild yeasts what can cause phenolic off flavour positive?

A

Spoilage bacteria

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41
Q

What characteristics do POF+ yeast impart?

A

Clove like through interaction with the malt that are important for German wheat beers - brewers avoid these flavours in other beer styles.

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42
Q

What flavour do brettanomyces yeasts impart?

A

Horsey or barnyard flavours due to 4 ethyl phenol production

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43
Q

How can phenol compounds be controlled?

A

By altering sparge time, sparge temp, wort pH and chlorine levels in water

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44
Q

What are the 6 products of fermentation (and maturation)?

A
  1. Ethanol (alcohol) C2H5OH
  2. Higher alcohols, also known as Fusel alcohols, e.g. propanol, butanol, amyl alcohol
  3. Organic acids formed (both volatile and non-volatile)
  4. Esters from interaction of organic acids and alcohols
  5. Aldehydes - add flavour
  6. Ketones - add flavour
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45
Q

Does ethanol add flavour to the beer?

A

Doesn’t directly have flavour but influences flavour delivery of other constituents

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46
Q

How do Fusel alcohols have an effect on flavour?

A

These will vary the alcohol perception but also introduce medicinal or fuel smells - the higher the fermentation temp, the higher the production of fusel alcohols produced. Also includes phenolic compounds.

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47
Q

How do organic acids effect beer flavour?

A

Includes fatty acids that affect both stability and flavour.

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48
Q

How do esters affect beer flavour?

A

Interaction of organic acids and alcohol e.g. ethyl acetate, these add to flavour. In beers only good in small amounts - excess leeds to off flavours, can also turn to off flavours at higher temps.

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49
Q

Why does sterilisation occur and when?

A
  • Essential to all post boil steps

- Boiled wort is a sugar solution so ideal for microorganisms to thrive in

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50
Q

How can sterilisation be carried out?

A
  • Boiling of bottles
  • Washing equipment in sodium metabisulphite (kills microorganisms)
  • Iodine/bleach/specialists sterilisation chemicals
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51
Q

What happens to equipment following sterilisation?

A

rinsed to remove flavour of sterilizing chemicals

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52
Q

What must happen to all equipment coming into contact with the boiled wort?

A

Sterilised

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53
Q

How does the pitching of yeast occur?

A
  • Important to sterilise vessels before yeast is added, many other microorganisms which could feed off wort
  • sterilise anything coming into contact with wort
  • yeast can be prestarted into a liquid form for more rapid mixing or added directly to wort in powder form
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54
Q

What does yeast require/ the wort need to provide for yeast to grow and multiply after pitching?

A
  • A carbon source (fermentable sugars)
  • A nitrogen source (amino acids) - aids growth and metabolism
  • Growth factors (vitamins)
  • Inorganic ions (minerals)
  • Oxygen
  • Water
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55
Q

What are the 2 ways that yeast ferments/metabolises sugar?

A
  • Aerobic (with oxygen) - products = co2 and h20 (initial growth and multiplication)
    Aerobic yields enough energy for yeast colony to multiply

-Anaerobic (without oxygen) - product = co2 and ethyl alcohol (ethanol) - eventually ethanol becomes toxic to yeast
Anaerobic doesn’t provide enough energy for yeast multiplication

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56
Q

What are the 4 phases in the fermentation life cycle?

A
  1. lag phase
  2. growth phase
  3. fermentation phase
  4. Sedimentation phase
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57
Q

What is the lag phase in fermentation of the wort?

A

1st stage
- Here the yeast strives to reproduce as fast as possible, the key growth ingredient is glycogen, contained within the yeast, which is broken down to glucose to fuel the yeast. Yeast low in glycogen or an insufficient amount leads to different flavours in the beer

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58
Q

What is the growth phase in fermentation of the wort?

A

2nd phase
- Here the yeast uses oxygen and nutrients to grow logarithmically. The yeast will continue to grow until oxygen or nutrients run out

59
Q

What is the fermentation phase in the fermentation of the wort?

A

3rd phase
- once all the oxygen has been scrubbed from the wort the yeast begins to convert the simple sugars into ethanol, co2 and beer flavours. This usually takes 3-7 days, the yeast at this stage is called ‘Krausen’

60
Q

What is the sedimentation phase in the fermentation of the wort?

A

Final stage
- Yeast forms into large masses which either sink to the bottom (lagers) or rise to the top (ales). The rate of sedimentation changes depending on the yeast type. This step can take days to week depending on yeast used. The yeast stores glycogen and enters a dormant phase. It can be used to ‘start’ another batch and start the cycle all over again.

61
Q

What do all saccharomyces yeast strains ferment?

A

Glucose and fructose (monosaccharides- hexose) vigorously - passive intake (with aid of permease enzymes) into the yeast for conversion

62
Q

What happens to maltose and maltriose during fermentation?

A

Actively transported across cell membrane and hydrolysed in cell cytosol to monosaccharides?

63
Q

What happens to sucrose during fermentation?

A

Sucrose cleaved by invertase outside of the yeast cell to glucose

64
Q

What happens to pentos (like xylose and arabinose), dextrans and larger starch breakdown products?

A

They’re not metabolised

65
Q

What happens to non fermentable sugars like lactose, stevia and xylitol during fermentation?

A

These are added to sweeten brews but lactose can be fermented by wild yeast

66
Q

How is glucose absorption by yeast generally represented?

A

C6h12o6 —–> 2(ch3ch2oh) + 2(co2)

Sugar = alcohol + carbon dioxide

67
Q

How many chemical reactions are there driven by different enzymes in yeast under anaerobic conditions?

A

14

68
Q

What is the anaerobic pathway (anaerobic glycolysis)?

A

Glycolytic pathway to pyruvate and then via acetaldehyde to ethanol

69
Q

What is the aerobic pathway?

A

Glycolytic pathway to pyruvate and then via glycerol formation

70
Q

What is the krebs cycle?

A

A series of chemical reactions used by aerobic organisms (in this case yeast) that converts carbohydrates (pyruvate) inot ATP and CO2
Cycle also produces amino acid precursors and a reducing agent NADH

71
Q

What is the energy source in the krebs cycle?

A

ATP

72
Q

When oxygen is present what does the yeast produce in the krebs cycle?

A

28 molecules of ATP from each glucose molecule

73
Q

When oxygen is not present what does the yeast produce in the krebs cycle?

A

2 molecules of ATP and so produces ethyl alcohol as a n alternative energy source

74
Q

What is the chemical responsible for hangovers?

A

Acetaldehyde - by product of fermentation

75
Q

What are the by products of fermentation?

A

methanol - fruits and fruit beers produce more than grains and wine
Not toxic in the low concentrations found in beer and wine

76
Q

How are the by products of fermentation such as methanol removed?

A

Distillation concentrates the methanol which is then metabolized to formic acid and formaldehyde in the body - can cause blindness - important to remove this during distillation

77
Q

What are most problems during fermentation due to?

A

The yeast

The temp at which fermentation occurs

78
Q

Why does too much yeast cause fermentation problems?

A
  • excessive competition for nutrients which leads to problems
79
Q

Why does too little yeast cause fermentation problems?

A
  • May take too long to reach the correct amounts to produce anaerobic conditions
80
Q

Why/what fermentation problems are more common with home brewers?

A
  • Small volumes more subject to temp fluctuations
    1. slow initial fermentation - yeast in unfamiliar environment
    2. Weak yeast strains give stuck fermentations with temp fluctuations
    3. varied alcohol tolerance of the yeast
    4. poor sterilisation leads to competition for food
    5. if mashed at too high temps, then there can be too many non-fermentable sugars - not enough food for the yeast
    6. Not enough nutrients introduced in recipe (low protein levels)
81
Q

What is stuck fermentation?

A

When the fermentation stops before desired original gravity is reached.
Can also have fermentations which don’t start or which proceed slowly (e.g. high gravity beers may ferment slow)

82
Q

How can stuck fermentation be reversed?

A

By bringing the fermentation vessel back to the fermentation temp (not too hot or cold)
Add more yeast - cannot add fresh yeast as it will be in lag phase, instead add yeast which is already in growth stach - a technique known as krausening

83
Q

What does krausening involve?

A

Making a sugar solution that you pitch yeast into, once it is fermenting vigorously you can pitch into your stuck ferment

84
Q

How is fermentation halted and why?

A
  • When final gravity is reached
  • Chilled to 9-11 C
  • Achieved by chilling plates inside fermenters and takes up to 2 days
85
Q

What happens after fermentation is halted?

A

Beer is ready to be removed from fermenters into casks or conditioning tanks

86
Q

What is green beer?

A

Beer immediately after the fermentation stage

87
Q

What happens to yeast after the sedimentation phase?

A
  • It goes dormant.
  • Yeast will rise to top if ale yeast (attach to Co2) OR sink if lager yeast
  • It can be harvested and used to start another fermentation
88
Q

How many times can yeast be reused before being spent?

A

5-6 times

89
Q

What is the typical volume of spent yeast collected from lager fermentation?

A

0.18kg/100L

90
Q

What happens to spent yeast?

A

Added to animal feed as a source of protein and water soluble vitamins
Also used as a nutritional source for humans and used as ingredient in food processing e.g. marmite

91
Q

What is raw beer?

A

Beer that skips the boiling step (as sterilisation processes are better)
- Usually dry hopped = aromas not bitterness

92
Q

Why is raw beer produced?

A

To ensure that flavour compound and aromas are kept which would have been lost during boil

93
Q

What ales were traditionally made without a boiling step?

A

Farmhouse - this is why flavours imparted by yeast were so important

94
Q

What happens regarding sterilization with raw beers?

A

Sterilization is key
- water must be boiled prior to mashing
some traditional raw ale brewers call it ‘again boiling’

95
Q

How is cider made?

A

By fermenting apple juice

  • apples are washed and ground to sauce
  • different blends of sauce are combined and then this pomace is pressed to get juice
  • Yeast added to ferment apple juice into cider- ABV = 1.2-8.5% (continental can go up to 12%)
  • 3.8 L of cider = 5-6Kg of apples
  • Aged from 3-6 months
96
Q

How is perry made?

A

By fermenting pear juice

  • pears are washed and ground into sauce
  • different blends of sauce are combined and then this pomace is pressed to get juice
  • Uses a wild yeast present on skins of pears
  • ABV = 1.2-8.5% (continental can go up to 12%)
  • 3.8 L of cider = 5-6Kg of pears
  • Aged from 3-6 months
97
Q

What is the original gravity?

A
  • The gravity of boiled wort prior to fermentation
  • It’s the ratio of the density of the wort to the density of water, measurement is directly related to amount of sugar in the wort
98
Q

How is original gravity measured?

A

Using a hydrometer

99
Q

What is the final gravity?

A

The gravity after fermentation, achieved when most of the sugars have fermented into ethanol

100
Q

What does beer that is less than 3% have?

A

Short shelf life

101
Q

When do most brewer’s yeast stop?

A

At 9% alcohol

102
Q

How do some beers gain higher levels of alcohol?

A

Using special yeasts - e.g. belgian beers use wine yeasts to ferment

103
Q

What are the strongest beers?

A

Up to 57.5% (concentrated using distillation or freeze concentration)

104
Q

What is the exact potential?

A

A measure of how effectively the sugars were mashed out of the grain

105
Q

Why is the exact potential and what should it typically be?

A

It lets you determine how effective your mash program was

60-80%

106
Q

How is exact potential calculated?

A

By determining the amount of sugar that was mashed out and dividing by the potential maximum sugar that could have been mashed out.

107
Q

When is dry hopping carried out?

A

Fermentation or conditioning

108
Q

What types of beers is dry hopping used for?

A

IPAs or Pale Ales

109
Q

What does dry hopping do in terms of flavour?

A

Only adds flavour and aroma

NO BITTERNESS

110
Q

How was dry hopping developed originally?

A

Adding hops to cask beer before it was shipped to customers

111
Q

What is a good process for adding volatile oils that would normally be boiled off?

A

Dry hopping

112
Q

How may drying hopping influence flavour negatively?

A

greasy/oily

113
Q

What is the general ratio during dry hopping?

A

30-100g per 19L of green beer

114
Q

What are the processes associated with beer conditioning?

A
  • Flavour/Aroma change- some compounds stick to yeasts as they settle or decompose- loss of diacetyl flavours
  • Carbonation from secondary fermentation - also stabilisation against non-biological haze.
  • Can have addition of colour/flavour - some high quality ales have added aroma hops into the barrel- fruit/flavoured beer
  • Non traditional filtering and pasteurisation for ‘bright’ beers - affects flavour
  • The longer the beer is stored the smoother it’ll be - trade off with the constantly dropping iso-alpha concentration. Lager beers do particularly well with a longer-term secondary fermentation. During this time the yeasts can work on the more complex sugars, but this is a slow process.
115
Q

What temperature are cask beers stored at?

A

12-150C

116
Q

How is venting during maturation controlled during cask conditioning?

A

controlled by a porous soft spile

117
Q

What happens prior to dispensing in cask beers?

A

The dissolved gas content is increased by inserting a hard spile

118
Q

How is carbonation achieved in cask beers?

A

By adding priming sugar

119
Q

What beer undergoes secondary fermentation? and what does this do?

A

Only in unpasteurised beer in a cask or bottle

- responsible for the sparkle in traditional ales

120
Q

How do carbonation levels vary?

A

From low (English ales) to high (German wheat beers)

121
Q

What is needed for secondary fermentation?

A

Residual sugars from first fermentation or new priming sugar added

122
Q

What are the different sugars that can be added for secondary fermentation?

A
  • Corn sugar/table sugar
  • Dry malt extract - if do not want to add sugar to beer
  • Krausening - using fresh wort to add carbonation
  • Carbonation tablets - precisely doses sugar for bottles
123
Q

How does secondary fermentation work?

A

The yeast feeds on the priming sugar and produces CO2, as long as the bottle is sealed then carbonation level can increase

124
Q

What gas do beers like smithwicks draught, guinness and kilkenny use for carbonation?

A

Nitrogen

instead of co2

125
Q

What is the makeup of nitro IPAs?

A

70% N2

30% CO2

126
Q

How is nitrogen added to beers?

A

Using a restrictor plate which forces the beer through tiny holes.

127
Q

Why is nitrogen used in beers?

A

Nitrogen bubbles stay small and so have a smoother ‘creamier’ mouthfeel - why it takes longer to pour a pint of nitro

128
Q

What happens to nitro when it is poured?

A

Nitrogen bubbles on the side of the glass flow downwards during the ‘surge’ due to the shape of the glass

129
Q

What is barrel ageing?

A

Strong ales/stouts are aged in wood in a similar fashion to whisky, bourbon and gin.
- Beer needs to be strong, so the flavour imparted by the wood does not wash out the beer flavour

130
Q

How long do bourbon and wood notes take to influence alcohol in barrel ageing?

A

1-2 months

131
Q

How long do floral and vanilla notes take to influence alcohol in barrel ageing?

A

6-12 months

132
Q

What has to happen to barrel aged beer before it’s bottled?

A

Racked - to ensure wood particles settle

133
Q

How are traditional ales carified?

A

By fining agents

134
Q

What does islinglass do in beer clarification?

A

Derived from fish bladders and binds the negatively charged yeast

135
Q

What do auxiliary finings do in beer clarification?

A

Bind positively charged proteins giving agglomerate which falls to bottom of cast.

136
Q

Why does top fermenting yeast rise to the top?

A

Because it binds to the co2

137
Q

Why is there less foam in lager?

A

Because lager yeast produces much less co2

138
Q

What leads to lager being a clearer beer?

A

Stored at cold temps for longer periods

139
Q

Give examples of unpasteurised beers and what does this mean?

A

Cask ale
Wild ales
- Essentially they’re living organisms

140
Q

Why are brewery conditioned beers filtered and pasteurised?

A

To ensure there is no bacterial activity

141
Q

How is beer pasteurised?

A

Involves raising the beer to certain temp, holding it there and then cooling back down - ensures all microorganisms are killed

142
Q

What sets pasteurisation time?

A

looking to kill most resistant microorganism

143
Q

What are the two pasteurisation temperatures and time?

A

72 C for 15 secs

60 C for 15 mins

144
Q

Summarise fermentation and conditioning (5)

A
  • Yeast has 4 phases of action: lag, growth, fermentation and sedimentation
  • Yeast produces energy by 2 mechanisms - aerobic and anaerobic (aerobic = growth phase, anaerobic = fermentation phase)
  • 2 main yeasts are used but additional yeasts are becoming more popular
  • Following fermentation, the beer is clarified and then conditioned in casks, bottles or kegs.
  • Various mechanisms controlling final amounts of bubbles in beers

Food 1130: Traditional alcoholic beverages (9 decks)

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