Steps to make yoghurt?
Reveal answer
Pasteurise → cool to 40 °C → add Lactobacillus → incubate → lactic acid thickens.
Key words: Lactobacillus
6(a) FOOD PRODUCTION · RECALL
6.7 Lactobacillus and yoghurt
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What does Lactobacillus make from lactose?
Reveal answer
Lactic acid.
Key words: lactic
Why does yoghurt thicken?
Reveal answer
Lactic acid → low pH → milk proteins coagulate.
Key words: coagulate
Why pasteurise milk first?
Reveal answer
Kill unwanted bacteria.
Key words: bacteria
What is meant by the term Lactobacillus?
Reveal answer
A genus of bacteria that ferment sugars to lactic acid.
Key words: Lactobacillus
What is meant by the term pasteurisation?
Reveal answer
Heat treatment that kills most microorganisms in a food.
Key words: pasteurisation
What is meant by the term incubation?
Reveal answer
Keeping a culture at a controlled temperature for growth.
Key words: incubation
Steps in yoghurt production: for Pasteurisation, give the conditions and the reason.
Reveal answer
Conditions: Heat milk, e.g. 85–95 °C. Reason: Kill unwanted microorganisms.
Key words: Pasteurisation
Steps in yoghurt production: for Cooling, give the conditions and the reason.
Reveal answer
Conditions: To about 40–45 °C. Reason: So added bacteria are not killed.
Key words: Cooling
Steps in yoghurt production: for Add starter culture, give the conditions and the reason.
Reveal answer
Conditions: Lactobacillus. Reason: Ferments lactose.
Key words: Add starter culture
Steps in yoghurt production: for Incubation, give the conditions and the reason.
Reveal answer
Conditions: About 40–45 °C for hours. Reason: Optimum for bacterial enzymes; lactic acid builds up.
Key words: Incubation
Steps in yoghurt production: for Cooling and storage, give the conditions and the reason.
Reveal answer
Conditions: Refrigeration. Reason: Slows further fermentation and spoilage.
Key words: Cooling and storage
True or false, and why? “Lactobacillus produces ethanol like yeast.”
Reveal answer
False. It produces lactic acid.
True or false, and why? “Pasteurisation sterilises milk completely.”
Reveal answer
False. It kills most, not all, microorganisms.
True or false, and why? “Yoghurt thickens because bacteria add protein.”
Reveal answer
False. Lactic acid lowers pH, causing existing milk proteins to coagulate.