Learn why your curd can become extremely thick and dense after a night in the fridge. Discover how the cold temperature affects its structure.
1 Answer
Curd thickens excessively in the fridge overnight due to the continued activity of lactic acid bacteria at cooler temperatures, albeit at a slower rate, leading to further coagulation of milk proteins. The cold temperature also reduces the whey separation, making the curd appear thicker.
Detailed Explanation:
The thickening of curd, also known as yogurt, is primarily due to the activity of lactic acid bacteria. These bacteria ferment lactose (milk sugar) into lactic acid. This acid lowers the pH of the milk, causing the milk proteins, mainly casein, to coagulate and form a solid or semi-solid mass – the curd.
While refrigeration slows down the bacterial activity, it doesn't completely stop it. The lactic acid bacteria continue to produce acid, albeit at a much reduced rate. Over several hours, such as overnight, this continued acid production leads to further coagulation of the proteins, resulting in a thicker curd.
Additionally, the cold temperature in the refrigerator also affects the whey (the liquid portion of the milk). At warmer temperatures, some whey might separate from the curd. However, at colder temperatures, the whey is less likely to separate, contributing to the overall thicker consistency of the curd. The water molecules are less energetic and less likely to break free from the protein matrix.
Pro Tip:
To prevent excessive thickening, consider using a shorter fermentation time at room temperature before refrigerating, or use a lower concentration of starter culture. This will reduce the amount of lactic acid produced and slow down the coagulation process.