Why should curd and sour substances not be kept in brass and copper vessels?
Curd and sour substances contain acids, which give them their characteristic sour taste. When these acidic substances are stored in brass and copper vessels, the acids present in them react with the metals.
Acids generate hydrogen gas on reacting with metals. This chemical reaction between the acid and the metal vessel can spoil the food substances and make them unfit for consumption.
Therefore, curd and sour substances should not be kept in brass and copper vessels to prevent such undesirable chemical reactions from occurring.
Explanation
The textbook context establishes that sour tastes in food are due to acids, and that acids react with metals to produce hydrogen gas. Curd and sour substances are acidic in nature. When stored in brass or copper vessels (which are metals), the acids react with the metal surface, leading to chemical reactions that can spoil the food. This is why such vessels are not recommended for storing acidic substances.
Solution Steps
Step 1: Identify that curd and sour substances contain acids (sour taste indicates presence of acids).
Step 2: Recognize that acids react with metals to produce hydrogen gas.
Step 3: Conclude that storing acidic substances in metal vessels causes undesirable reactions.