Semester 2- Alcohol -role of microorganisms Flashcards
Brewing
manufacture of alcoholic beverages from malted grains
two main types of brewery yeast strains
- top fermenting (ales)
- bottom fermenting (lagers)
beer yeasts
-ability to produce fermentation, flocculate, desired products (aroma and flavour)
starter culture
-from previous batches or pure strains
Malting
Barley –> Malt
Malt
contains various enzymes amylases (starch–>maltose) and proteases essential for the brewing process
Dried malt
enzymes stable
Mashing
Malt–>grist–>wort
Fermentation :ALE
- batch fermentation in large open vats
- top fermenting yeast
- strains of Saccharomyces cerevisiae
- 5-6 days
- aerated
Fermentation: LAGER
- produced by closed batch fermentation
- use of bottom feeding yeasts
- strains of Saccharomyces carlsbergensis
- 8-14 days
Maturation
- storage, finishing, distribution
- lager stored at -1, ale at 4-8
Chemistry
Maltose–>glucose–>pyruvate–>acteladehyde + CO2–>ethanol
Maturation = esters
Spoilage
certain bacteria and yeasts cause spoilage of beer due to :
- low pH
- alcohol content
- hop extracts
- low storage temps
- anaerobic conditions
Examples of spoilage organisms:
- lactobacillus (acidity)
- Acetobacter )souring)
- Wild yeast (EG S.pasteurianus)
- Pediococcus cervisiae (diacetyl)
Spoilage prevented by:
- aseptic and hygiene precautions
- regular cleaning and sterilisation of equipment
- use of pure strains
- pasteurisation