Question 7 of 11intermediate🔍 AnalyzeShort Answer3 marks

A student observes that when curd is left out for a day, it becomes more sour. What can be two possible explanations for this observation?

Correct Answer

Two possible explanations for curd becoming more sour when left out:

First, Lactobacillus bacteria present in curd continue to ferment lactose (milk sugar) at room temperature, producing more lactic acid which increases the sourness.

The warmer room temperature compared to refrigerator accelerates bacterial activity and fermentation.

Second, when left at room temperature, the bacterial population multiplies faster, leading to increased fermentation and more lactic acid production.

The continuous bacterial activity breaks down more lactose into lactic acid over time, making the curd progressively more sour.

Exercise: Keep the curiosity alive | Q: 8 | (Page Page 19)
For More Understanding

Explanation

Activity 2.9 in the chapter explains that Lactobacillus bacteria in curd feed on lactose sugar in milk, multiply, and ferment milk to form curd. These bacteria produce lactic acid, which makes curd sour. The chapter states that these bacteria grow well in warm conditions, which is why curd forms in bowl A kept in a warm place but not in bowl B kept in a refrigerator. When curd is left at room temperature, the warm conditions allow Lactobacillus to remain active and continue producing lactic acid.

Solution Steps

  1. Lactobacillus bacteria ferment lactose (milk sugar) to produce lactic acid, which causes sourness

  2. Room temperature accelerates bacterial activity and fermentation compared to refrigeration

  3. Bacterial population multiplies faster at room temperature, leading to increased fermentation

  4. Continuous bacterial activity produces more lactic acid over time, making curd progressively more sour

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