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Y2S1_FST2110 - Microbiology and fermentation > Lect 9 : Beer Fermentation > Flashcards

Lect 9 : Beer Fermentation Flashcards

1
Q

What is the purpose of beer fermentation ? [2]

A
  1. shelf life extension
  2. Conversion of raw material (grains) into more functional form(?)
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2
Q

What is the major crop used in beer fermentation?

A

Barley, a major crop that is a mahor crop for human and animal consumption

  • it is a source of malt (cereal grains that have been soaked and dried)
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3
Q

What is the composition of barley? [7]

A
  1. starch
  2. sugars – glucose, maltose, dextrins (oligosacc)
  3. Partially hydroysed protein/peptide/AA
  4. Lipid
  5. β-glucan
  6. soluble hemicellulose
  7. Insoluble cellulose
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4
Q

What are adjuncts and what is their purposes? [2]

A

They are unmalted (ungerminated) grains apart from barley, cheaper forms of carbohydrates

  1. enhance physical stability of beer –> lowering protein : carb ratio (less protein = less precipitation)
  2. provides distinct flavour to beer (flavour differs for different types of adjuncts)
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5
Q

What is hop?

A

It is a kind of herb (flower from plant)

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6
Q

What is the purpose of adding hops into beer? [4]

A
  1. Preservation – have α/β acids to inhibit growth of gram positive bacteria
  2. Aroma – herb/floral/citrusy/fruity
  3. Taste – contributes to bitterness
  4. Precipitation of proteins due to tannins
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7
Q

What are the 4 distinct stages of making beer ?

A
  1. Malting (germination)
  2. Wort preparation (liquid extracted from the mashing process during the brewing of beer or whisky.)
  3. Fermentation
  4. Post-fermentation
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8
Q

[STAGE 1 : MALTING]

What are the 2 stages involved in malting?

A
  1. Steeping and germination
  2. Drying and kilning
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9
Q

[STAGE 1 : MALTING]

How to germinate barley grains?

What is the purpose of steeping and germination?

A

Germinate by mixing grains with water and changing water every few days to minimise impact of spoilage MO

Purpose: Maximise enzyme synthesis (protease/amylase/peptidase)

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10
Q

[STAGE 1 : MALTING]
What are the 3 purposes of kilning?

A
  1. Stop further germination
  2. Preserve/stabilize enzymes by slow drying with dry heat
  3. Maillard reaction –> flavour and colour generation
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11
Q

[STAGE 1 : MALTING]

In kilning, how does duration of heating affect the type of beer you get?

A

Short-time : beer has highest moisture content, more sugars and least brown in colour

Longest time : less amylase, less sugar, less ethanol and more brown (dark beer)

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12
Q

[STAGE 2 : WORT (liquid) PREPARATION]

What are the 5 stages in wort preparation?

A
  1. Milling
  2. Mashing
  3. Lautering
  4. Kettle boil
  5. Whirlpool
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13
Q

[STAGE 2 : WORT (liquid) PREPARATION]

What is milling the purpose of milling?

A

To break malt kernel and expose interior to aqueous medium
.
.
Purpose : To produce fine particle sizes for easy extraction of enzyme and components

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14
Q

[STAGE 2 : WORT (liquid) PREPARATION – MASHING]

What is a problem with excessive milling of malt?

A

Although it can increase extraction efficiency of nutrients and enzymes, the fine particles may clog filters and affect filtration

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15
Q

[STAGE 2 : WORT (liquid) PREPARATION]
What is mashing?

A

It is the process of extracting enzymes and converting starch/protein from grist (milled malt) and adjuncts into fermentable sugars/amino acids to produce wort

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16
Q

[STAGE 2 : WORT (liquid) PREPARATION]
What conditions are needed in mashing to prepare a wort with desired sugar/amino acid composition?

A

Heating the wort at certain temperatures while adjusting the amount of time

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17
Q

[STAGE 2 : WORT (liquid) PREPARATION – MASHING]

In mashing, the grist is heated stepwise, and at different temperatures. Why?

A

Different enzymes have different optimal temperatures (e.g. amylase, protease)

Heat stepwise to match optimal temperatures of different enzymes so that enzyme can break down substrate

18
Q

[STAGE 2 : WORT (liquid) PREPARATION – MASHING]

The biochemical reactions happening during mashing can be generalised as “rest”. What kinds of “rest” is happening?

A

“Rest” : allow time for reaction to occur (hydrolysis for protein and starch)

  1. Acid rest
  2. Protein rest
  3. Saccharification rest (sugars)
19
Q

[STAGE 2 : WORT (liquid) PREPARATION – MASHING]
How is acid rest carried out and what is its purpose?

A

brewing with yeast (traditional method) / direct acidification
.
.
Purpose : to inhibit growth of spoilage MO and ensuring clean fermentation process.

20
Q

[STAGE 2 : WORT (liquid) PREPARATION – MASHING]

What happens during protein rest? What are its purposes? [2]

A

Higher molecular weight (MW) proteins are digested into lower MW proteins/peptides and amino acids
.
.
Purposes :
1. Improve foam stability
2. Decrease haze/ precipitation due to high molecular weight proteins

21
Q

[STAGE 2 : WORT (liquid) PREPARATION – MASHING]

What is the purpose of saccharification rest?

A

Hydrolyse starch into more digestible forms for yeast consumption during fermentation

Starch –> dextrins/maltose/glucose

22
Q

[STAGE 2 : WORT (liquid) PREPARATION – LAUTERING]

What is the purpose of lautering?

A

To separate liquid wort from insoluble material

23
Q

[STAGE 2 : WORT (liquid) PREPARATION – LAUTERING]

Lautering first step : mashing out

What is mashing out and its 2 purposes?

A

Increasing temperature to 77°C

  1. To stop enzymatic reaction
  2. Make mash more fluid to facilitate reaction
24
Q

[STAGE 2 : WORT (liquid) PREPARATION – LAUTERING]

Lautering step 2 : recirculation

What is recirculation and its purpose?

A

Drawing off wort from bottom of mash tun (vessel) and putting it to the top

Purpose : Maximize extraction of sugars

25
Q

[STAGE 2 : WORT (liquid) PREPARATION – LAUTERING]

Lautering step 3 : sparging

What is sparging and its purposes

A

To rinse spent grain bed with water

Purpose:
1. to extract more sugars
2. Dilute liquor

26
Q

[STAGE 2 : WORT (liquid) PREPARATION – BOILING]

What is added to the wort when boiling?

A

Hop

27
Q

[STAGE 2 : WORT (liquid) PREPARATION – BOILING]

What are the purposes of wort boiling [7]?

A
  1. Sterilisation : iso-α acid inhibits growth of gram positive bacteria
  2. Inactivate enzymes
  3. Flavour extraction (isomerisation of less bitter α acid to more bitter iso α acid)
  4. Colour development (Maillard)
  5. Loss of volatiles
  6. Oxidation
  7. Increase concentration of wort by removing water
28
Q

[STAGE 3 : FERMENTATION]

What are 3 stages involved in beer fermentation?

A
  1. Cooling
  2. Fermentation
  3. Conditioning and maturation
29
Q

[STAGE 3 : FERMENTATION]

What temperature is lager beer and ale beer cooled to?

A

Lager : 10-15°C
Ale :16-20°C

30
Q

[STAGE 3 : FERMENTATION]

What changes happen during cooling of beer?

A
  1. Formation and separation of “cold break” (sediments)
  2. Aeration (inject oxygen) to support yeast growth
31
Q

[STAGE 3 : FERMENTATION]

What specific species ferments ale and lager beer?

A

Ale beer : fermented by “top” fermenting yeast : Saccharomyces Cerevisae

Lager beer : by “bottom yeasts” : Saccharomyces Pastorianus

32
Q

[STAGE 3 : FERMENTATION]

Why cant be fermentation temperatures be too high/low?

A

Too low : extended lag phase, causing inactivity and yeast may be dormant due to cold shock

Too high : ferment too fast –> temperature of beer rises further from fermentation –> causing fermentation to be stuck

33
Q

[STAGE 3 : FERMENTATION]

What are the minor but important products of yeast ferm, other than ethanol?

A
  1. Higher alcohols (alcohols with >2C)
  2. Acids – acetic acid
  3. Esters
  4. Ketones, aldehydes
    ᴖ̈ acetaldehyde – green apple flavour
    ᴖ̈ diacetyl – butterscotch aroma (undesirable in ale/lager beer)
34
Q

[STAGE 3 : FERMENTATION – conditioning and maturation]

Under what reaction is lager beer conditioned/matured? What temperature is it at?

A

Diacetyl rest, where temperature is raised from 10-15°C to 16-20°C

35
Q

[STAGE 3 : FERMENTATION – conditioning and maturation]

What is the purpose of diacetyl rest?

A
  • Yeast reuptake diacetyl in the media to break down into acetoin and 2,3-butanediol
  • as diacetyl introduces off flavours in lager beer, and 2,3-butanediol has a higher detection threshold (need more to detect)
36
Q

[STAGE 4 : POST-FERMENTATION]
What is the 2 stages of post-fermentation?

A
  1. Clarification and filtration
  2. Packaging and pasteurisation
37
Q

[STAGE 4 : POST-FERMENTATION]
What is the purpose and filtration? What else is done to the beer and what 2 purposes does it serve?

A

Filtration to remove yeast and solid residues (tannin-protein agglomerates)
- Tannin from hops

Carbonation is also done.
1. Shelf life extension (preventing growth of other aerobic spoilage microbes)
2. Enhance foaming property of beer (CO2 creates bubbles)

38
Q

[STAGE 4 : POST-FERMENTATION]
What is the purpose of pasteurization? In which 2 ways can pasteurization be conducted?

A

Pasteurisation is to provide sterilation

Ways to pasteurise :
1. Before filling –> flash pasteurisation (71-74°C for 30s)
1. After filling in bottle –> tunnel pasteurisation

39
Q

What are the spoilage organisms in beer? [3]

A
  1. Wild yeast
  2. LAB (esp gram positive LAB which can resist iso-α-acids in hops)
  3. Acetic acid bacteria
40
Q

NOVELTY BEER : SOUR BEER (LAMBIC BEER)
Which microbe is responsible for fermenting sour beer? Which 2 specific species could be used?

A

LAB (can be homo/hetero)

  1. Lactobacillus
  2. Pediococcus
41
Q

What are the 2 major problems with lambic beer?

A
  1. Controlling of acetic acid, due to the oxidation of ethanol by acetobacter
  2. Brettanomyces yeast: produces Brett flavour which is undesirable
    - Ethyl phenol : smokey/medicinal taste
  3. Acetic acid
  4. Ethyl lactate

Y2S1_FST2110 - Microbiology and fermentation (12 decks)

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