Describe how bacteria are used in the production of yoghurt from milk.

WJEC GCSE Biology (Wales) — 2.7 Micro-organisms and their applications · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Bacteria are added to warm milk
Bacteria ferment the lactose (sugar) in the milk
Lactic acid is produced during fermentation
The lactic acid causes the milk to thicken / curdle / become more acidic, forming yoghurt

Examiner tips

Use the exact sequence of steps: inoculation, fermentation, acid production, thickening
Show the role of lactic acid bacteria (e.g. *Lactobacillus* spp.)
Keep the answer concise – 4 points, no extra detail

Common mistakes

Confusing the bacteria with the milk itself, e.g. saying "milk is added to bacteria"
Mentioning other acids or processes not relevant to yoghurt production

Mark scheme (4 marks)

Bacteria are added to warm milk
Bacteria ferment the lactose (sugar) in the milk
Lactic acid is produced during fermentation
The lactic acid causes the milk to thicken / curdle / become more acidic, forming yoghurt

Key terms in this question

bacteria