Useful Microorganisms

Question 1

How do we make yogurt?

Answer 1

1) All equipment is sterilised
2) Milk is pasteurised by heating it to 78*C
3) When milk cools down it is incubated with a culture of bacteria (lactobacillus) which causes the breakdown of lactose to make lactic acid, which makes the yogurt taste acidic
4) Followed by sampling, adding flavours, colours and packaging

Question 2

What does the process of fermentation of yeast involve?

Answer 2

Aerobic respiration:
C6H12O6 —> 2C2H5OH + 2CO2
glucose —-> ethanol + carbon dioxide

Question 3

How do we make alcoholic drinks?

Answer 3

1) Sugar is extracted by crushing barley or grapes
2) Yeast is added
3) Kept warm and allowed to ferment, air and other microbes are kept out
4) Wine or beer is allowed to clarify and the clear liquid is drawn off (removed from yeast sediment)
5) Wine or beer is then pasteurised (kills harmful microbes)

Question 4

Why do we use distillation to make spirits?

Answer 4

Concentration of alcohol made by fermentation is limited because high concentrations of alcohol kill yeast cells.

Question 5

What happens to the oxygen in brewing?

Answer 5

All oxygen is used up quickly by yeast respiring aerobically, this allows the number of cells to increase rapidly. Conditions are then kept anaerobic so alcohol is made.

Question 6

What affects the rate at which yeast breaks down sugar?

Answer 6

• Temperature

- Oxygen levels