Cooking Patterns > Food Processing Patterns

Pasteurized Milk

Pasteurization is a process in which foods are treated with mild heat to eliminate pathogens and extend shelf life, or scalding heat when you want to denature the proteins in the food for further processing.

Pasteurizing milk with scalding heat is a pattern that is used when preparing yogurt and paneer (Indian cottage cheese). You cannot make yogurt or paneer from milk without first pasteurizing it.

Pasteurizing milk at home, for yogurt and paneer, means bringing the milk to a boil on the stove and then turning off the heat. This heating process denatures the proteins in the milk. Denature means to break the bonds in the protein molecules that keep them in their folded shape, so that they all stretch out into strands.

Milk pasteurization is done in the exact same way for both yogurt and paneer. Milk is put in a pot and heated on the stove until it boils.

To make yogurt and paneer, the denatured proteins from the pasteurized milk are forced into coagulation using acid. Coagulation is when all the denatured proteins bond together, forming a solid or semi-solid. While the same coagulation process is done to form both yogurt and paneer, it is done in different ways and at different speeds.

Let’s now see the coagulation methods used to create yogurt and paneer.

Yogurt

When making yogurt, the milk is left out after pasteurization to come back down to room temperature. Then a starter culture is mixed in with the milk. The bacteria in the starter culture slowly ferment the milk and convert the lactose sugar into lactic acid over a period of 6 hours. The slow release of lactic acid causes the systematic coagulation of the denatured proteins in the milk. Because this acidification process is slow and steady, the milk gets evenly coagulated into a consistent semi-solid gel.

Note, milk contains sugar, proteins, fat, and water. When the milk is denatured and then slowly coagulated to make yogurt, the semi-solid mesh of proteins that is created traps a lot of the water and fat from the milk. But some of the water doesn’t get incorporated into the protein mesh, which is why you see a small pool of water at the bottom of the yogurt container when you make homemade yogurt.

On another note, Greek yogurt is made in the exact same way as regular yogurt but with one additional step. After the yogurt is made, it is poured into a cheesecloth so that most of the water can be mushed out. Greek yogurt is the same yogurt, only thicker because it has much less water.

Here is a demonstration of how to make yogurt at home:

Paneer

When making paneer, an acid, usually lemon juice or vinegar, is immediately added to the milk after pasteurization. This direct addition of acid is used in place of the slow fermentation and acidification process used to create yogurt.

When acid is added to the milk all at once, it causes a violent chemical reaction and results in the rapid coagulation of the denatured proteins. Because the coagulation occurs so quickly, the proteins don’t form a consistent mesh. Instead, the proteins quickly coagulate into curdles of cheese that float to the top of the milk. This curdling happens until all the proteins coagulate into cheese and the cheese is completely separated from the water.

The cheese is then scooped out of the milk and put into a cheesecloth so it can be balled up and squeezed to release the water and bind the chunks together. The cheese is then left aside, still in the cloth, to set into shape.

Here is a demonstration of how to make paneer at home: