Beer part 4: Fermentation Flashcards
(144 cards)
1
Q
What family do yeast belong to?
A
Fungus.
Fungi are the principal decomposers of the ecological kingdom
2
Q
How many subclasses of yeast are there?
A
3 - one is saccharomycetacea, this contains 4 groups, one of which is saccharomycoidea
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
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)
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
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
7
Q
Why does yeast produce smells?
A
To attract fruit flies to help with dispersion of the yeasts into the environment
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
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
10
Q
What is lager yeast?
A
Saccharomyces Pastorianus (formerly - Carlsbergensis)
11
Q
When and where was lager yeast isolated?
A
Late 19th century
Carlsberg laboratories - given away freely to other breweries
12
Q
Where is the genetic sequencing of lager yeast?
A
Early stages
13
Q
What has recently been discovered regarding lager yeast?
A
It is a hybrid of s.Cerevisiae and S. Eubayanus
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
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
16
Q
What yeast does Heineken use?
A
A proprietary yeast called A yeast - has used the same yeast for more than a century
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
18
Q
Why were beers traditionally sour tasting?
A
Wild yeast used to ferment it added sour flavours.
19
Q
Why is beer generally now not sour?
A
Modern yeast cultures don’t add sour compounds
20
Q
How are sour flavours intentionally added to beer?
A
Using wild yeast or bacteria
21
Q
Why is trying to create sour beers risky?
A
As may not create safe/nice tasting beer
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
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
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
25
What is the malt blend of a lambic beer?
70% barley malt and 30% unmalted wheat
26
Why are large amounts of hops used in a lambic beer?
Because the long inoculation and fermentation times required by wild yeast increase risk of spoilage
27
What type of hops do modern lambics use and why?
Old dry hops that are less hoppy and flavourful but still have antiseptic properties
28
How are lambic beers drunk/stored?
Rarely bottled as is
| Draught releases are categorized as old or young depending on fermentation time - can be bracingly sour
29
What is Gueze?
Mix of one and two year old lambics, secondary fermentation happens in bottle
30
What is a kriek?
Lambic fermented in the presence of cherries
31
What are fruit lambics?
Lambic mixed with berries/grapes/stone fruits/ tropical fruits
32
What sour beers have been released recently?
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
33
What are some new strains of yeast that have been identified in relation to wild beers?
- Cultivated from the skins of peaches
- Cultivated from a San Francisco sourdough starter
- Cultivated from plum skins
34
What is rogue ales bear beer?
American wild ale, brewed from yeast collected on the beard of the brew master - said to have sharp pineapple flavour
35
What is mikkeller beer greek brunch weasel
An imperial oatmeal stout made with cape cut chon coffee beans collected from civet droppings - pre difested inside the civet
36
What is the other main flavour compound besides esters?
Phenols (spice instead of fruit)
37
How are yeasts classified in terms of phenols?
Phenolic Off Flavour positive of negative (POF+/-)
38
Generally speaking what are wild yeasts in terms of phenols?
POF+
39
Generally speaking what are commercial yeasts in terms of phenols?
POF-
40
Other than wild yeasts what can cause phenolic off flavour positive?
Spoilage bacteria
41
What characteristics do POF+ yeast impart?
Clove like through interaction with the malt that are important for German wheat beers - brewers avoid these flavours in other beer styles.
42
What flavour do brettanomyces yeasts impart?
Horsey or barnyard flavours due to 4 ethyl phenol production
43
How can phenol compounds be controlled?
By altering sparge time, sparge temp, wort pH and chlorine levels in water
44
What are the 6 products of fermentation (and maturation)?
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
45
Does ethanol add flavour to the beer?
Doesn't directly have flavour but influences flavour delivery of other constituents
46
How do Fusel alcohols have an effect on flavour?
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.
47
How do organic acids effect beer flavour?
Includes fatty acids that affect both stability and flavour.
48
How do esters affect beer flavour?
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.
49
Why does sterilisation occur and when?
- Essential to all post boil steps
| - Boiled wort is a sugar solution so ideal for microorganisms to thrive in
50
How can sterilisation be carried out?
- Boiling of bottles
- Washing equipment in sodium metabisulphite (kills microorganisms)
- Iodine/bleach/specialists sterilisation chemicals
51
What happens to equipment following sterilisation?
rinsed to remove flavour of sterilizing chemicals
52
What must happen to all equipment coming into contact with the boiled wort?
Sterilised
53
How does the pitching of yeast occur?
- 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
54
What does yeast require/ the wort need to provide for yeast to grow and multiply after pitching?
- A carbon source (fermentable sugars)
- A nitrogen source (amino acids) - aids growth and metabolism
- Growth factors (vitamins)
- Inorganic ions (minerals)
- Oxygen
- Water
55
What are the 2 ways that yeast ferments/metabolises sugar?
- 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
56
What are the 4 phases in the fermentation life cycle?
1. lag phase
2. growth phase
3. fermentation phase
4. Sedimentation phase
57
What is the lag phase in fermentation of the wort?
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
58
What is the growth phase in fermentation of the wort?
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
What is the fermentation phase in the fermentation of the wort?
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
What is the sedimentation phase in the fermentation of the wort?
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
What do all saccharomyces yeast strains ferment?
Glucose and fructose (monosaccharides- hexose) vigorously - passive intake (with aid of permease enzymes) into the yeast for conversion
62
What happens to maltose and maltriose during fermentation?
Actively transported across cell membrane and hydrolysed in cell cytosol to monosaccharides?
63
What happens to sucrose during fermentation?
Sucrose cleaved by invertase outside of the yeast cell to glucose
64
What happens to pentos (like xylose and arabinose), dextrans and larger starch breakdown products?
They're not metabolised
65
What happens to non fermentable sugars like lactose, stevia and xylitol during fermentation?
These are added to sweeten brews but lactose can be fermented by wild yeast
66
How is glucose absorption by yeast generally represented?
C6h12o6 -----> 2(ch3ch2oh) + 2(co2)
| Sugar = alcohol + carbon dioxide
67
How many chemical reactions are there driven by different enzymes in yeast under anaerobic conditions?
14
68
What is the anaerobic pathway (anaerobic glycolysis)?
Glycolytic pathway to pyruvate and then via acetaldehyde to ethanol
69
What is the aerobic pathway?
Glycolytic pathway to pyruvate and then via glycerol formation
70
What is the krebs cycle?
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
What is the energy source in the krebs cycle?
ATP
72
When oxygen is present what does the yeast produce in the krebs cycle?
28 molecules of ATP from each glucose molecule
73
When oxygen is not present what does the yeast produce in the krebs cycle?
2 molecules of ATP and so produces ethyl alcohol as a n alternative energy source
74
What is the chemical responsible for hangovers?
Acetaldehyde - by product of fermentation
75
What are the by products of fermentation?
methanol - fruits and fruit beers produce more than grains and wine
Not toxic in the low concentrations found in beer and wine
76
How are the by products of fermentation such as methanol removed?
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
What are most problems during fermentation due to?
The yeast
| The temp at which fermentation occurs
78
Why does too much yeast cause fermentation problems?
- excessive competition for nutrients which leads to problems
79
Why does too little yeast cause fermentation problems?
- May take too long to reach the correct amounts to produce anaerobic conditions
80
Why/what fermentation problems are more common with home brewers?
- 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
What is stuck fermentation?
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
How can stuck fermentation be reversed?
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
What does krausening involve?
Making a sugar solution that you pitch yeast into, once it is fermenting vigorously you can pitch into your stuck ferment
84
How is fermentation halted and why?
- When final gravity is reached
- Chilled to 9-11 C
- Achieved by chilling plates inside fermenters and takes up to 2 days
85
What happens after fermentation is halted?
Beer is ready to be removed from fermenters into casks or conditioning tanks
86
What is green beer?
Beer immediately after the fermentation stage
87
What happens to yeast after the sedimentation phase?
- 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
How many times can yeast be reused before being spent?
5-6 times
89
What is the typical volume of spent yeast collected from lager fermentation?
0.18kg/100L
90
What happens to spent yeast?
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
What is raw beer?
Beer that skips the boiling step (as sterilisation processes are better)
- Usually dry hopped = aromas not bitterness
92
Why is raw beer produced?
To ensure that flavour compound and aromas are kept which would have been lost during boil
93
What ales were traditionally made without a boiling step?
Farmhouse - this is why flavours imparted by yeast were so important
94
What happens regarding sterilization with raw beers?
Sterilization is key
- water must be boiled prior to mashing
some traditional raw ale brewers call it 'again boiling'
95
How is cider made?
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
How is perry made?
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
What is the original gravity?
- 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
How is original gravity measured?
Using a hydrometer
99
What is the final gravity?
The gravity after fermentation, achieved when most of the sugars have fermented into ethanol
100
What does beer that is less than 3% have?
Short shelf life
101
When do most brewer's yeast stop?
At 9% alcohol
102
How do some beers gain higher levels of alcohol?
Using special yeasts - e.g. belgian beers use wine yeasts to ferment
103
What are the strongest beers?
Up to 57.5% (concentrated using distillation or freeze concentration)
104
What is the exact potential?
A measure of how effectively the sugars were mashed out of the grain
105
Why is the exact potential and what should it typically be?
It lets you determine how effective your mash program was
| 60-80%
106
How is exact potential calculated?
By determining the amount of sugar that was mashed out and dividing by the potential maximum sugar that could have been mashed out.
107
When is dry hopping carried out?
Fermentation or conditioning
108
What types of beers is dry hopping used for?
IPAs or Pale Ales
109
What does dry hopping do in terms of flavour?
Only adds flavour and aroma
| NO BITTERNESS
110
How was dry hopping developed originally?
Adding hops to cask beer before it was shipped to customers
111
What is a good process for adding volatile oils that would normally be boiled off?
Dry hopping
112
How may drying hopping influence flavour negatively?
greasy/oily
113
What is the general ratio during dry hopping?
30-100g per 19L of green beer
114
What are the processes associated with beer conditioning?
- 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
What temperature are cask beers stored at?
12-150C
116
How is venting during maturation controlled during cask conditioning?
controlled by a porous soft spile
117
What happens prior to dispensing in cask beers?
The dissolved gas content is increased by inserting a hard spile
118
How is carbonation achieved in cask beers?
By adding priming sugar
119
What beer undergoes secondary fermentation? and what does this do?
Only in unpasteurised beer in a cask or bottle
| - responsible for the sparkle in traditional ales
120
How do carbonation levels vary?
From low (English ales) to high (German wheat beers)
121
What is needed for secondary fermentation?
Residual sugars from first fermentation or new priming sugar added
122
What are the different sugars that can be added for secondary fermentation?
- 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
How does secondary fermentation work?
The yeast feeds on the priming sugar and produces CO2, as long as the bottle is sealed then carbonation level can increase
124
What gas do beers like smithwicks draught, guinness and kilkenny use for carbonation?
Nitrogen
| instead of co2
125
What is the makeup of nitro IPAs?
70% N2
| 30% CO2
126
How is nitrogen added to beers?
Using a restrictor plate which forces the beer through tiny holes.
127
Why is nitrogen used in beers?
Nitrogen bubbles stay small and so have a smoother 'creamier' mouthfeel - why it takes longer to pour a pint of nitro
128
What happens to nitro when it is poured?
Nitrogen bubbles on the side of the glass flow downwards during the 'surge' due to the shape of the glass
129
What is barrel ageing?
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
How long do bourbon and wood notes take to influence alcohol in barrel ageing?
1-2 months
131
How long do floral and vanilla notes take to influence alcohol in barrel ageing?
6-12 months
132
What has to happen to barrel aged beer before it's bottled?
Racked - to ensure wood particles settle
133
How are traditional ales carified?
By fining agents
134
What does islinglass do in beer clarification?
Derived from fish bladders and binds the negatively charged yeast
135
What do auxiliary finings do in beer clarification?
Bind positively charged proteins giving agglomerate which falls to bottom of cast.
136
Why does top fermenting yeast rise to the top?
Because it binds to the co2
137
Why is there less foam in lager?
Because lager yeast produces much less co2
138
What leads to lager being a clearer beer?
Stored at cold temps for longer periods
139
Give examples of unpasteurised beers and what does this mean?
Cask ale
Wild ales
- Essentially they're living organisms
140
Why are brewery conditioned beers filtered and pasteurised?
To ensure there is no bacterial activity
141
How is beer pasteurised?
Involves raising the beer to certain temp, holding it there and then cooling back down - ensures all microorganisms are killed
142
What sets pasteurisation time?
looking to kill most resistant microorganism
143
What are the two pasteurisation temperatures and time?
72 C for 15 secs
| 60 C for 15 mins
144
Summarise fermentation and conditioning (5)
- 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
