Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

The pH of fresh milk will decrease as it turns into curd, becoming more acidic. This change in pH is primarily due to the fermentation process involved in curd formation. Here’s how the pH change occurs during the curd formation process:

1. Fresh Milk (pH 6): Fresh milk typically has a pH around 6, making it slightly acidic. This acidity is primarily due to the presence of lactic acid and other weak organic acids naturally found in milk.

2. Fermentation Process: The conversion of milk into curd is a result of bacterial fermentation. Lactic acid bacteria, such as Lactobacillus bulgaricus and Streptococcus thermophilus, are commonly used to ferment milk.

3. Lactic Acid Production: During the fermentation process, the lactic acid bacteria consume the lactose (milk sugar) present in the milk. They metabolize lactose and convert it into lactic acid. This lactic acid production is responsible for the decrease in pH. Lactic acid is a stronger acid than the weak organic acids initially present in milk.

4. Decrease in pH: As lactic acid accumulates in the milk, the pH of the solution decreases. The increase in the concentration of lactic acid ions (H+) leads to a more acidic environment. This change in pH is what causes the milk to curdle and form curd.

The acidic environment created by the lactic acid bacteria is crucial for curd formation. It denatures the milk proteins, causing them to coagulate and form a solid structure. This coagulation process, along with the lower pH, results in the characteristic texture and taste of curd.

So, as milk turns into curd, the pH decreases from its initial slightly acidic value of around 6 to a lower, more acidic pH due to the accumulation of lactic acid produced during the fermentation process.