B6c: Useful microorganisms

Question 1

Main stages in making yoghurt (6)

Answer 1

equipment sterilised to kill unwanted microbes

pasteurisation of milk - heated to kill most bacteria, then cooled

incubation of culture in fermenter with a culture of bacteria; bacteria reproduce w/ milk as food source

Lactobacillus bacteria break down lactose in the milk into lactic acid, causing milk to clot and solidify into yoghurt

sample taken; quality control; added to next batch

add flavours, colours, packaging

Question 2

word equation for fermentation (anaerobic respiration in yeast)

Answer 2

glucose (sugar) → ethanol (alcohol) + carbon dioxide

Question 3

Balanced chemical equation for fermentation (anaerobic respiration)

Answer 3

C6H12O6 → 2C2H5OH + 2CO2

Question 4

Main stages in brewing (7)

Answer 4

malting(barley seeds germinate, enzymes convert starch in seeds into sugar)

extracting sugar from source material (source material is crushed)

flavouring

adding yeast to keep it warm

fermentation while keeping air and other microorganisms out

allow the wine or beer to clarify and extract it

pasteurising and packaging/bottling

Question 5

Describe the adding yeast and fermentation stage (4)

Answer 5

yeast added, mixture kept warm to increase rate of respiration to produce alcohol and give it better flavor

container sealed to prevent air (to ensure anaerobic) and other microbes entering

when all oxygen used up, yeast anaerobically respires, ferments sugar into alcohol

if too much oxygen in container, yeast respire aerobically instead, vinegar is produced

Question 6

Describe what is meant by the term pasteurisation and explain why this needs to be done in the case of bottled beers(2)

Answer 6

product heated and quickly cooled to kill any remaining microbes/yeast, stops fermentation

reduce ­risk of bottled beers spoiling if not stored in right conditions, increase shelf life

Question 7

How is fermentation limited? (2

Answer 7

higher conc of ethanol (toxic) due to anaerobic respiration starts to kill yeast, ­reduce rate of respiration and fermentation

different strains of yeast tolerate different alcohol concentration, resulting in drinks with diff alcohol concentration

Question 8

How is the alcohol concentration increased? (4+1)

Answer 8

mixture from fermentation process is distilled

placed in large container and heated

alcohol boils ~80C (