As Fresh milk has a pH of 6, when it changes into curd (Yoghurt), will its pH value increases or decreases? Why?

Acidic and basic are two extremes that describe a chemical property. The pH scale measures how acidic or basic a substance is. 
The pH scale ranges from 0 to 14. The pH value of-
  • Basic solution is greater than 7.
  • Neutral solution is equal to 7.
  • Acidic solution is less than 7.
The pH value of milk is 6 since it is acidic in nature. When the milk is converted into curd, due to the action of bacteria, lactic acid is formed which is more acidic in nature. Therefore the pH value of the milk is reduced because curd contains acid so H+ increases and thus pH will decrease.

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