Curd becomes sour because bacteria like Lactobacillus multiply in warm conditions, producing lactic acid. The acid gives curd its sour taste. Higher temperatures speed up this bacterial growth and souring process.
class 8 science chapter 2 the invisible living world beyond our naked eye question answer
Class 8 Science Curiosity Textbook Chapter 2 The Invisible Living World – Beyond Our Naked Eye question answer
When curd is left at room temperature, especially in warmth, bacteria like Lactobacillus multiply quickly. They convert the lactose in milk into lactic acid, which gives the curd a sour taste. The longer it’s left out, the more acid forms, making it more sour. This is a clear example of microbial activity changing the taste and composition of food naturally.
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