Lecture 10: Beer and Brewing Flashcards
What are different types of beer?
Ales
Porters
Stouts
Lagers
What is the history of beer and brewing?
One of the oldest biotechnological processes
First records: Egypt 6,000 BC
First microorganism to be grown in pure culture: Saccharomyces carlsbergenesis (Carlberg yeast number 1)
Pure strain brewing carried out for first time in 1883 at Carlberg brewery in Denmark
What are the main stages of brewing
- Malting
- Mashing
- Boiling
- Fermentation
- Post-fermentation and packaging
What is ‘malting’?
- Steeping. Barley soaked in water (10-16C) for ~40hr
a. germination
b. amylase activation - Germination. 3-5 days at 16-19C on mashing floor to a depth
of 20cm - Kilning. Germinated barley is heated to high temperature
a. drying at 50-60C
b. curing at 80-110C
c. ‘malt’
What is ‘mashing’?
- Miling. Malt and adjuncts milled to fine powder (‘grist’)
- Mashing. Grist mixed with hot water (‘liquor’) in mash tun
a. 60-70C - Saccharification. starch converted to mono-, di- and tri-
saccharides
a. ‘wort’ (sugar-rich liquid) - Lautering. Wort is strained through bottom of the mash tun
What is boiling?
- Hopping. Wort obtained from the mash is transferred to a ‘copper’ and hops or hop extracts are added
What is hops?
The flower cones of the female hop vine (Humulus lupulus). Gives beer its characteristic bitter flavour. Also has antiseptic properties that help keep beer from spoiling
What is fermentation?
- Pitching. Yeast is added to the cooled wort
- Fermentation. Sugars in the wort are converted to alcohol
Ales & stouts. 18-26C (typically 20C). Top-fermenting yeasts.
Lager. 8-15C (typically 10C). Bottom-fermenting yeasts
What are the two types of yeasts?
Top- and bottom-fermenting yeasts
What are top-fermenting yeasts
Make ales and stouts.
They have flocculation behaviour.
Unable to ferment the disaccharide melibiose
Include: Saccharomyces cerevisiae
What are bottom-fermenting yeasts?
used to produce lager, and produced sedimentary flocculation. They also contain melibiase. meaning they can ferment melibiose
Include: Saccharomyces pastorianus, S. carlsbergenesis
What is pitching?
Yeasts for fermentation can be grown from stock cultures but more often yeast is taken from a previous fermentation. Can occur up to 5-10 times.
Adding yeast is called “pitching”
Spent/surplus yeast can be dried, used for animal feeds, or turned into yeast extract
What do yeasts need to grow?
- Energy source: from fermentable carbohydrate
- Nitrogen source: from peptides and amino acids
- Minerals: calcium, magnesium, phosphorus, sulfur, copper,
and zinc - Growth factors: biotin and pantothenate
What are different flavour compounds
- alpha-acids and iso-alpha-acids: add bitterness
- Amino acids: concentration and spectrum of wort amino
acids important for microbial growth. Aromatic alcohols are
derived from wort amino acids - Esters: Formed by condensing an acid with an alcohol. Only
in traces but important for flavour
a. ethyl acetate (solvent aroma)
b. Isoamyl acetate (banana aroma)
c. Phenyl ethyl acetate (roses and honey)
d. Ethyl caproate (sour apple)
What is post fermentation?
Green beer (what’s left after fermentation and yeast removal) has to be matured or conditioned before consumption. Maturation for lagers and ales depends on the rate of removal of diketones diacetyl and 2,3 pentanedione .
Cask & bottled ales-priming sugar is added to allow remaining yeast to do secondary fermentation and carbonate the beer. Other things like hops can also be added
What is lagering?
Post fermentation process
Lager held in tank at 8C for several weeks. No priming sugars added, but remaining yeasts continue to ferment the wort sugar. This also generates CO2, which purges the beer to remove volatile compounds
What is storage ageing?
Post fermentation process
Most common large scale process. No further sugar added, and beer is stored at 1-4C for 7-10 days to encourage chill-haze particle formation, which is removed by filtration
What are areas for strain improvement?
- Better utilization of nutrients within the wort
a. maltose is major fermentable sugar, but process is
incomplete
b. The uptake of sugar is the rate limiting step, taken in by
maltose permease
c. Genes which encode maltose transporters can be cloned
into yeast strains, producing GM Yeast - Better flocculation properties
a. Essential for removal of yeast post fermentation
b. Reversible and calcium dependent process
c. Flocs form as an interaction between adhesins with
mannan carbohydrates.
d. Ideally, yeast flocs after the wort sugars have been
fermented
e. Different yeast strains have different flocculation properties - Better filterability
- Reduction of bad flavours
- Healthy beer
What is Lg-Flo1
Adhesin present in S. pastorianus. The gene ensures that flocculation only occurs after wort sugars have been utilized.
FLO gene expression can be controlled to give a variety of flocculation properties
How is low alcohol beet made
Removal of alcohol post fermentation, resulting in loss of essential aroma compounds and worty taste.
Can be done by altering carbon flow, making yeast strains over express GPD1 glycerol formation
How is low calorie beer made
Reducing dextrin content
Dextrin: D-glucose polymers derived from starch
Amylases could be introduced into yeast
