Useful Microorganisms

Question 1

The process of making yogurt uses bacteria and includes a number of steps:

Answer 1

• First, all the equipment is sterilised.
• Then milk is pasteurised by heating it to above 78°C.
• When the milk is cooled down it is incubated with a culture of bacteria.
• This is followed by sampling and then adding flavours, colours and packaging.

Question 2

What is added to milk to make yogurt?

Answer 2

The type of bacterium that is added to the milk of lactobacillus. This causes the breakdown of lactose in milk to lactic acid, which makes yoghurt tastes acidic.

Question 3

Ethanol Symbol

Answer 3

C₂H₅OH

Question 4

What is the word Eq. for fermentation?

Answer 4

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

Question 5

Using this reaction, yeast can be used in brewing beer or wine:

Answer 5

• First, the sugar is extracted by crushing grapes (wine) or from barley grains (beer).
• Then yeast is added.
• It is kept warm to allow it to ferment. Air and other microorganisms are kept out.
• The wine or beer is allowed to clarify. The clear liquid is then drawn off (removed from the yeast sediment).

Question 6

How is whiskey and brandy made?

Answer 6

The concentration of alcohol made by fermentation is limited, so to make drinks like whiskey and brandy the process of distillation is used. This increases alcohol concentration but is only allowed in licensed premises.

Question 7

Symbol Eq. for fermentation

Answer 7

C₆H₁₂O₆ ⇒ 2C₂H₅OH + 2CO₂

Question 8

What does yeast do when brewing?

Answer 8

When yeast is used in brewing it soon uses up all the oxygen in the container by respiring aerobically. This allows the number of cells to increase rapidly. Then conditions are kept anaerobic so that alcohol is made.

Question 9

Yeast breaks down sugar at different rates in different conditions:

Answer 9

• such as temperature,
• The presence or absence of oxygen

Question 10

Why is pasteuristation used?

Answer 10

The process of pasteurisation is used in brewing to kill harmful microbes. The liquid is kept at an elevated temperature for predetermined time. The temperature and time depends on the drink that is being brewed.

Question 11

Why is alcohol concentration in brewing limited?

Answer 11

This is because high concentrations of alcohol kill yeast cells, although some strains of yeast are more resistant to alcohol than others.