A milkman adds a small amount of baking soda to milk. This makes the pH of the milk

Fresh milk typically has a pH of approximately 6.6 to 6.8, making it slightly acidic. When a milkman adds a small amount of baking soda (sodium hydrogencarbonate), it acts as a mild alkaline substance. Baking soda reacts with the lactic acid produced by bacteria in the milk, thereby neutralizing the acidity and shifting the pH toward the alkaline side. This process makes the milk weakly alkaline. The primary purpose of this addition is to prevent the milk from curdling or souring too quickly, as alkaline conditions hinder the growth of spoilage-causing bacteria like Lactobacillus. While sodium bicarbonate is a base, the small quantity added ensures the milk does not become strongly alkaline, but rather shifts just enough to prolong its shelf life.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Uses of Baking soda > p. 31