9. Beer and brewing

History

  • One of the oldest biotechnology processes.

  • First records date to Egypt in 6,000B.C

  • The first microorganism to be grown in pure culture was Saccharomyces carlsbergenesis (Carlsberg Yeast number 1).

  • Pure strain brewing carried out for the first time, in 1883 at the Carlsberg brewery in Denmark.

Main stages

  1. Malting

  2. Mashing

  3. Boiling

  4. Fermentation

  5. Post-fermentation and packaging

1. Malting

Steeping. Barley is soaked in water (10-16oC) for ~40 h

→ germination.

→ amylase activation

Germination. 3-5 days at 16-19oC on a mashing floor to a depth of 20 cm.

Kilning. The germinated barley is heated to high temperature.

  • drying at 50-60oC

  • curing at 80-110oC

→ ‘malt’

2. Mashing

Milling. The malt and adjuncts milled to a fine powder (grist)

Mashing. Grist mixed with hot water (‘liquor’) in the mash tun.

  • 60-70oC

  • Saccharification: starch converted to mono-, di-, and tri-saccharides

  • → wort (sugar-rich liquid)

Lautering. Wort is strained through the bottom of the mash tun.

3. Boiling

Hopping. The wort obtained from the mash is transferred to a ‘copper’ (‘kettle’) and hops or hop extracts are added.

Hops are the flower cones of the female hop vine (Humulus lupulus). Hops give the beer its characteristic bitter flavour. They also have an antiseptic properties that help keep the beer from spoiling.

Boiling.

  • → End of enzyme reactions.

  • → Protein precipitation.

  • → Isomerisation of the hop α acids (humulones) to the more bitter tasting iso-α acids.

  • → Formation of melanoidins and oxidation of phenolic compounds.

  • → Concentration of the wort.

  • → Sterilisation of the wort.

Filtering.

The wort is filtered in the hopback to remove solids, including hop residues and precipitated protein (= trub)

More hops may be added to the hopback to increase flavour (replacing aromatics lost in the boil)

4. Fermentation

Pitching → Yeast is added to the cooled wort

Yeasts for fermentation can be grown from stock cultures, but more often yeast is taken from a previous fermentation. This can occur up to 5-10 times. Adding the yeast is called pitching.

Spent/surplus yeast can be dried, used for animal feeds or turned into yeast extract.

Fermentation – sugars in the wort are converted to alcohol.

  • Ales and stouts. 18-26oC (typically 20oC). Top-fermenting yeasts.

  • Lager. 8-15oC (typically 10oC). Bottom-fermenting yeasts.

Top-fermenting yeasts are used to make ales and stouts. They have flotational flocculation behaviour. They are unable to ferment the disaccharide melibiose (α-1,6- linked D-galactose and glucose).

Bottom-fermenting yeasts are used to produce lager, and produced sedimentary flocculation. They also contain melibiase, which means that they can ferment melibiose.

What do yeasts need to grow?

  • Energy source → provided by the fermentable carbohydrate

  • A nitrogen source taken from peptides and amino acids.

  • Minerals, such as calcium, magnesium, phosphorous and sulphur, also traces of copper and zinc

  • Growth factors such as biotin and pantothenate

Flavour compounds

  • α acids and iso-α acids

    • Add bitterness

  • Amino acids

    • Concentration and spectrum of wort amino acids important for microbial growth, but also for beer flavour, as aromatic alcohols are derived from wort amino acids

  • Esters

    • Formed by condensing an acid with an alcohol. They are trace compounds in beer, but crucial for flavour.

      • Ethyl acetate (solvent aroma)

      • Isoamyl acetate (banana aroma)

      • Phenyl ethyl acetate (roses and honey)

      • Ethyl caproate (sour apple)

5. Post Fermentation

After fermentation and removal of the majority of the yeast, the ‘green’ beer 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 and bottled ales-priming sugar is added to allow the remaining yeast to do a secondary fermentation to carbonate the beer. Other additions can be added e.g. hops.

Lagering - lager beer is held in a tank at 8oC for several weeks. No priming sugars are added, but the remaining yeasts continue to ferment the wort sugar. This also generates CO2 which purges the beer to remove volatile compounds.

Storage ageing is the most common large scale process. No further sugar is added, the beer is stored at 1-4 oC for 7-10 days to encourage chill-haze particles to form, which are removed by filtration.

Areas for Strain Improvement:

  1. Better utilisation of nutrients within the wort.

  2. Better flocculation properties.

  3. Better filterability.

  4. Reduction of bad flavours.

  5. Healthy beer.

Better utilisation of nutrients

  • Maltose is the major fermentable sugar, but the process in incomplete.

  • The uptake of the sugar is the rate limiting step. It is taken in by maltose permease.

  • The genes which encode maltose transporters can be cloned into yeast strains, producing a GM Yeast.

Flocculation

  • This property is essential in the removal of the yeast post fermentation.

  • Flocculation is a reversible and calcium dependent process. Cells stick to each other to form flocs.

  • Flocs are formed as an interaction between adhesins with mannan carbohydrates. Both have to be present on the cell surface.

  • Ideally, you want the yeast to floc, after the wort sugars have been fermented.

  • But different yeast strains have different flocculation properties.

  • Lg-Flo1 is present in S. pastorianus, the adhesin that this gene encodes ensures that flocculation will only happen after the wort sugars have been utilised. As long as wort sugars are present, they bind to the adhesin and inhibit flocculation.

  • The expression of the FLO genes can be controlled to give a variety of different flocculation properties.

Healthy Beer Low alcohol

  • Most low alcohol beer is made by removing the alcohol post fermentation.

  • This can mean the loss of essential aroma compounds and a ‘worty’ taste.

  • This can be done by altering the carbon flow. Yeast strains can be made which over express the GPD1 gene for glycerol formation, when used in fermentation they produce a low alcohol beer.

Low Calorie Beer

  • To get a low calorie beer, the dextrin content must be reduced.

  • Dextrins are D-glucose polymers (linear glycosidic α-1,4 and branched glycosidic α-1,6 linkages) – oligosaccharides derived from starch

  • Amylases could be introduced into yeast

Gluten-free beer

  • Gluten-free beer uses fermentable carbohydrate sources that don’t content gluten like rice or corn.