Lecture 10: Beer and Brewing

Question 1

What are different types of beer?

Answer 1

Ales
Porters
Stouts
Lagers

Question 2

What is the history of beer and brewing?

Answer 2

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

Question 3

What are the main stages of brewing

Answer 3

1. Malting
2. Mashing
3. Boiling
4. Fermentation
5. Post-fermentation and packaging

Question 4

What is ‘malting’?

Answer 4

1. Steeping. Barley soaked in water (10-16C) for ~40hr
   a. germination
   b. amylase activation
2. Germination. 3-5 days at 16-19C on mashing floor to a depth
   of 20cm
3. Kilning. Germinated barley is heated to high temperature
   a. drying at 50-60C
   b. curing at 80-110C
   c. ‘malt’

Question 5

What is ‘mashing’?

Answer 5

1. Miling. Malt and adjuncts milled to fine powder (‘grist’)
2. Mashing. Grist mixed with hot water (‘liquor’) in mash tun
   a. 60-70C
3. Saccharification. starch converted to mono-, di- and tri-
   saccharides
   a. ‘wort’ (sugar-rich liquid)
4. Lautering. Wort is strained through bottom of the mash tun

Question 6

What is boiling?

Answer 6

1. Hopping. Wort obtained from the mash is transferred to a ‘copper’ and hops or hop extracts are added

Question 7

What is hops?

Answer 7

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

Question 8

What is fermentation?

Answer 8

1. Pitching. Yeast is added to the cooled wort
2. 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

Question 9

What are the two types of yeasts?

Answer 9

Top- and bottom-fermenting yeasts

Question 10

What are top-fermenting yeasts

Answer 10

Make ales and stouts.

They have flocculation behaviour.

Unable to ferment the disaccharide melibiose

Include: Saccharomyces cerevisiae

Question 11

What are bottom-fermenting yeasts?

Answer 11

used to produce lager, and produced sedimentary flocculation. They also contain melibiase. meaning they can ferment melibiose

Include: Saccharomyces pastorianus, S. carlsbergenesis

Question 12

What is pitching?

Answer 12

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

Question 13

What do yeasts need to grow?

Answer 13

1. Energy source: from fermentable carbohydrate
2. Nitrogen source: from peptides and amino acids
3. Minerals: calcium, magnesium, phosphorus, sulfur, copper,
   and zinc
4. Growth factors: biotin and pantothenate

Question 14

What are different flavour compounds

Answer 14

1. alpha-acids and iso-alpha-acids: add bitterness
2. Amino acids: concentration and spectrum of wort amino
   acids important for microbial growth. Aromatic alcohols are
   derived from wort amino acids
3. 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)

Question 15

What is post fermentation?

Answer 15

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

Question 16

What is lagering?

Answer 16

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

Question 17

What is storage ageing?

Answer 17

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

Question 18

What are areas for strain improvement?

Answer 18

1. 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
2. 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
3. Better filterability
4. Reduction of bad flavours
5. Healthy beer

Question 19

What is Lg-Flo1

Answer 19

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

Question 20

How is low alcohol beet made

Answer 20

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

Question 21

How is low calorie beer made

Answer 21

Reducing dextrin content

Dextrin: D-glucose polymers derived from starch

Amylases could be introduced into yeast