Question

Approximately how much quantity of 1% citric acid solution is required to coagulate one litre of fresh cow milk at 80$^{\circ}$C?}

• A. 200 ml
• B. 150 ml
• C. 300 ml
• D. 900 ml

Hint:

Using a diluted coagulant (such as 1--2% citric acid) prevents localized over-acidification, helping to produce a soft, cohesive curd with uniform moisture distribution.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Acid coagulation of milk involves reducing the pH to the isoelectric point of casein (\(\text{pH} \approx 4.6\)) using an acidulant.
In chhana making, the concentration and volume of the coagulant solution are controlled to ensure complete precipitation without over-acidifying the curd.

Step 2: Detailed Explanation:
Standard dairy processing protocols indicate that approximately 2 to 2.4 grams of anhydrous citric acid are required to completely coagulate one liter of cow milk.
A 1% citric acid solution contains 1 gram of citric acid per 100 ml of solution.
To provide the 2 grams of citric acid required for coagulation, we can calculate the necessary volume of the 1% solution:
\[ \text{Volume of solution} = \frac{\text{Mass of citric acid required}}{\text{Concentration of solution}} \] \[ \text{Volume of solution} = \frac{2\,\text{g}}{0.01\,\text{g/ml}} = 200\,\text{ml} \] Using 200 ml of a 1% solution ensures that the acid is sufficiently diluted.
This dilution prevents localized over-acidification at the point of addition, which can result in a hard, grainy curd.
It also helps maintain the temperature of the milk during coagulation at around 80$^{\circ}$C, which is ideal for producing a soft, spongy chhana.

Step 3: Final Answer:
Therefore, approximately 200 ml of 1% citric acid solution is required per liter of cow milk.