Lect 9 : Beer Fermentation Flashcards
What is the purpose of beer fermentation ? [2]
- shelf life extension
- Conversion of raw material (grains) into more functional form(?)
What is the major crop used in beer fermentation?
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)
What is the composition of barley? [7]
- starch
- sugars – glucose, maltose, dextrins (oligosacc)
- Partially hydroysed protein/peptide/AA
- Lipid
- β-glucan
- soluble hemicellulose
- Insoluble cellulose
What are adjuncts and what is their purposes? [2]
They are unmalted (ungerminated) grains apart from barley, cheaper forms of carbohydrates
- enhance physical stability of beer –> lowering protein : carb ratio (less protein = less precipitation)
- provides distinct flavour to beer (flavour differs for different types of adjuncts)
What is hop?
It is a kind of herb (flower from plant)
What is the purpose of adding hops into beer? [4]
- Preservation – have α/β acids to inhibit growth of gram positive bacteria
- Aroma – herb/floral/citrusy/fruity
- Taste – contributes to bitterness
- Precipitation of proteins due to tannins
What are the 4 distinct stages of making beer ?
- Malting (germination)
- Wort preparation (liquid extracted from the mashing process during the brewing of beer or whisky.)
- Fermentation
- Post-fermentation
[STAGE 1 : MALTING]
What are the 2 stages involved in malting?
- Steeping and germination
- Drying and kilning
[STAGE 1 : MALTING]
How to germinate barley grains?
What is the purpose of steeping and germination?
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)
[STAGE 1 : MALTING]
What are the 3 purposes of kilning?
- Stop further germination
- Preserve/stabilize enzymes by slow drying with dry heat
- Maillard reaction –> flavour and colour generation
[STAGE 1 : MALTING]
In kilning, how does duration of heating affect the type of beer you get?
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)
[STAGE 2 : WORT (liquid) PREPARATION]
What are the 5 stages in wort preparation?
- Milling
- Mashing
- Lautering
- Kettle boil
- Whirlpool
[STAGE 2 : WORT (liquid) PREPARATION]
What is milling the purpose of milling?
To break malt kernel and expose interior to aqueous medium
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Purpose : To produce fine particle sizes for easy extraction of enzyme and components
[STAGE 2 : WORT (liquid) PREPARATION – MASHING]
What is a problem with excessive milling of malt?
Although it can increase extraction efficiency of nutrients and enzymes, the fine particles may clog filters and affect filtration
[STAGE 2 : WORT (liquid) PREPARATION]
What is mashing?
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
[STAGE 2 : WORT (liquid) PREPARATION]
What conditions are needed in mashing to prepare a wort with desired sugar/amino acid composition?
Heating the wort at certain temperatures while adjusting the amount of time
[STAGE 2 : WORT (liquid) PREPARATION – MASHING]
In mashing, the grist is heated stepwise, and at different temperatures. Why?
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
[STAGE 2 : WORT (liquid) PREPARATION – MASHING]
The biochemical reactions happening during mashing can be generalised as “rest”. What kinds of “rest” is happening?
“Rest” : allow time for reaction to occur (hydrolysis for protein and starch)
- Acid rest
- Protein rest
- Saccharification rest (sugars)
[STAGE 2 : WORT (liquid) PREPARATION – MASHING]
How is acid rest carried out and what is its purpose?
brewing with yeast (traditional method) / direct acidification
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Purpose : to inhibit growth of spoilage MO and ensuring clean fermentation process.
[STAGE 2 : WORT (liquid) PREPARATION – MASHING]
What happens during protein rest? What are its purposes? [2]
Higher molecular weight (MW) proteins are digested into lower MW proteins/peptides and amino acids
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Purposes :
1. Improve foam stability
2. Decrease haze/ precipitation due to high molecular weight proteins
[STAGE 2 : WORT (liquid) PREPARATION – MASHING]
What is the purpose of saccharification rest?
Hydrolyse starch into more digestible forms for yeast consumption during fermentation
Starch –> dextrins/maltose/glucose
[STAGE 2 : WORT (liquid) PREPARATION – LAUTERING]
What is the purpose of lautering?
To separate liquid wort from insoluble material
[STAGE 2 : WORT (liquid) PREPARATION – LAUTERING]
Lautering first step : mashing out
What is mashing out and its 2 purposes?
Increasing temperature to 77°C
- To stop enzymatic reaction
- Make mash more fluid to facilitate reaction
[STAGE 2 : WORT (liquid) PREPARATION – LAUTERING]
Lautering step 2 : recirculation
What is recirculation and its purpose?
Drawing off wort from bottom of mash tun (vessel) and putting it to the top
Purpose : Maximize extraction of sugars
[STAGE 2 : WORT (liquid) PREPARATION – LAUTERING]
Lautering step 3 : sparging
What is sparging and its purposes
To rinse spent grain bed with water
Purpose:
1. to extract more sugars
2. Dilute liquor
[STAGE 2 : WORT (liquid) PREPARATION – BOILING]
What is added to the wort when boiling?
Hop
[STAGE 2 : WORT (liquid) PREPARATION – BOILING]
What are the purposes of wort boiling [7]?
- Sterilisation : iso-α acid inhibits growth of gram positive bacteria
- Inactivate enzymes
- Flavour extraction (isomerisation of less bitter α acid to more bitter iso α acid)
- Colour development (Maillard)
- Loss of volatiles
- Oxidation
- Increase concentration of wort by removing water
[STAGE 3 : FERMENTATION]
What are 3 stages involved in beer fermentation?
- Cooling
- Fermentation
- Conditioning and maturation
[STAGE 3 : FERMENTATION]
What temperature is lager beer and ale beer cooled to?
Lager : 10-15°C
Ale :16-20°C
[STAGE 3 : FERMENTATION]
What changes happen during cooling of beer?
- Formation and separation of “cold break” (sediments)
- Aeration (inject oxygen) to support yeast growth
[STAGE 3 : FERMENTATION]
What specific species ferments ale and lager beer?
Ale beer : fermented by “top” fermenting yeast : Saccharomyces Cerevisae
Lager beer : by “bottom yeasts” : Saccharomyces Pastorianus
[STAGE 3 : FERMENTATION]
Why cant be fermentation temperatures be too high/low?
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
[STAGE 3 : FERMENTATION]
What are the minor but important products of yeast ferm, other than ethanol?
- Higher alcohols (alcohols with >2C)
- Acids – acetic acid
- Esters
- Ketones, aldehydes
ᴖ̈ acetaldehyde – green apple flavour
ᴖ̈ diacetyl – butterscotch aroma (undesirable in ale/lager beer)
[STAGE 3 : FERMENTATION – conditioning and maturation]
Under what reaction is lager beer conditioned/matured? What temperature is it at?
Diacetyl rest, where temperature is raised from 10-15°C to 16-20°C
[STAGE 3 : FERMENTATION – conditioning and maturation]
What is the purpose of diacetyl rest?
- 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)
[STAGE 4 : POST-FERMENTATION]
What is the 2 stages of post-fermentation?
- Clarification and filtration
- Packaging and pasteurisation
[STAGE 4 : POST-FERMENTATION]
What is the purpose and filtration? What else is done to the beer and what 2 purposes does it serve?
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)
[STAGE 4 : POST-FERMENTATION]
What is the purpose of pasteurization? In which 2 ways can pasteurization be conducted?
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
What are the spoilage organisms in beer? [3]
- Wild yeast
- LAB (esp gram positive LAB which can resist iso-α-acids in hops)
- Acetic acid bacteria
NOVELTY BEER : SOUR BEER (LAMBIC BEER)
Which microbe is responsible for fermenting sour beer? Which 2 specific species could be used?
LAB (can be homo/hetero)
- Lactobacillus
- Pediococcus
What are the 2 major problems with lambic beer?
- Controlling of acetic acid, due to the oxidation of ethanol by acetobacter
- Brettanomyces yeast: produces Brett flavour which is undesirable
- Ethyl phenol : smokey/medicinal taste - Acetic acid
- Ethyl lactate
