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Food production

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Question 14

A student researched the industrial process for manufacturing yoghurt and found the following production guidelines:

  • Heat fresh milk in a vat to 90 ∘C90\text{ }^\circ\text{C}90 ∘C and maintain this temperature for 15 minutes.
  • Cool the milk down to 42 ∘C42\text{ }^\circ\text{C}42 ∘C.
  • Inoculate the milk with a starter culture containing active lactic acid bacteria.
  • Incubate the mixture at 42 ∘C42\text{ }^\circ\text{C}42 ∘C for 6 hours to allow fermentation.
  • Cool the yoghurt rapidly to 4 ∘C4\text{ }^\circ\text{C}4 ∘C to stop the fermentation process before packaging.
a.

Name a genus of bacterium typically added in the starter culture to ferment milk into yoghurt.

[1]
b.

Explain why the milk is heated to 90 ∘C90\text{ }^\circ\text{C}90 ∘C at the start of the process.

[2]
c.

Explain why the milk must be cooled to 42 ∘C42\text{ }^\circ\text{C}42 ∘C before adding the starter culture bacteria.

[2]
d.

Explain why the mixture is kept at a warm temperature of 42 ∘C42\text{ }^\circ\text{C}42 ∘C for 6 hours.

[2]
e.

During fermentation, the accumulation of lactic acid causes a significant drop in pH. Describe and explain how this decrease in pH helps to preserve the yoghurt and affects its texture.

[3]
Markscheme

Food production Questions

  1. IGCSE
  2. /Biology
  3. /Food production

74 exam-style questions on Edexcel IGCSE Biology Food production. Each one has a worked solution and a mark scheme showing where the marks go.

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