MCQ Detailed View

Milk is a natural colloidal solution composed of water, proteins, lactose (milk sugar), fats, minerals, and vitamins. One of the key chemical properties of milk is its pH, which indicates whether it is acidic, neutral, or basic. The normal pH of fresh cow’s milk falls between 6.5 and 7.0, making it slightly acidic to almost neutral.

The reason milk is not exactly neutral (pH 7) is due to the presence of dissolved carbon dioxide, casein proteins, and trace amounts of organic acids such as lactic acid. Freshly drawn milk is closer to pH 6.7. Over time, if milk is not refrigerated, bacterial activity converts lactose into lactic acid, lowering the pH further. This increasing acidity is what causes milk to spoil and curdle.

To understand this better, recall the pH scale:

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  pH 0–6 → acidic

  
  


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  pH 7 → neutral

  
  


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  pH 8–14 → basic

  
  

Since milk lies between 6.5 and 7, it is slightly on the acidic side but still very close to neutral. This mild acidity is important for its natural flavor and stability.

In the dairy industry, pH measurement is a crucial analytical test for quality control. Fresh milk with pH below 6.5 may indicate bacterial contamination, while a pH higher than 7 could suggest abnormal changes in composition. For cheese and yogurt production, lowering the milk pH intentionally through lactic acid bacteria is an essential step to achieve the desired texture and taste.

For comparison:

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  Human blood has a pH of around 7.4 (slightly basic).

  
  


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  Lemon juice has a pH of about 2 (strongly acidic).

  
  


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  Soap solution has a pH around 9–10 (basic).

  
  

Thus, the pH of milk being 6.5 – 7 places it close to neutral, but just slightly acidic, which is why milk tastes mild and not sour unless it spoils.