Question

Gerber acid used for fat estimation of milk has a density of ___________ at 27°C.

• A. 1.807 - 1.812
• B. 1.840 - 1.882
• C. 1.870 - 1.882
• D. 1.832 - 1.852

Hint:

Remember that concentrated commercial sulfuric acid has a density of \(1.84\ \text{g/mL}\).
For the Gerber test, this acid must be slightly diluted to a density of \(1.807 - 1.812\ \text{g/mL}\) to prevent charring of the milk sugars during digestion.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The Gerber method is a volumetric method used to estimate the fat content of milk and dairy products.
It relies on using concentrated sulfuric acid to digest the milk proteins (casein), which destabilizes the fat globule membrane.
This allows the fat to separate as a clear, distinct layer, which is then measured in a graduated butyrometer.

Step 2: Detailed Explanation:
The concentration of the sulfuric acid used in this test is critical.
- If the acid is too concentrated (high density), it will char the lactose and proteins, producing dark, caramelized particles that obscure the fat column interface.
- If the acid is too dilute (low density), it will fail to fully digest the proteins, leaving an incomplete separation of fat and a cloudy column.
To achieve optimum digestion without charring, the sulfuric acid is prepared to a specific concentration.
According to the Bureau of Indian Standards (BIS) and standard dairy laboratory protocols (such as IS 1224), the sulfuric acid used in the Gerber test must have a density between \(1.807\) and \(1.812\ \text{g/mL}\) at 27°C.
This corresponds to a sulfuric acid concentration of approximately 90% to 91% by weight.
Standard laboratory grade concentrated sulfuric acid has a density of approximately \(1.84\ \text{g/mL}\) (around 98% concentration), which is too strong and must be carefully diluted to meet the Gerber specifications.

Step 3: Final Answer:
The density of the Gerber sulfuric acid used for fat estimation must be between 1.807 and 1.812 g/mL at 27°C.