Why do things curdle

The protein in milk is normally suspended in a colloidal colloid solution, which means that the small protein molecules float around freely and independently. Along with the suspended fats, these floating protein molecules refract light. Normally these protein molecules repel each other, allowing them to float about without clumping, but when the pH of their solution changes, they can attract one another and form clumps. This is what happens when milk curdles.

When pH levels drop in milk, it turns acidic and milk protein casein and others molecules attract one another to form "curdles" or lumps. These lumps then float on the surface of the solution. The lumps are formed faster at warmer temperatures.

When we add lime juice in boiling milk, the acid present in the lime disturbs the pH level of the milk and the protein molecules begin to form large chains. These chains of protein molecules separate themselves from water molecules and form a sediment or what we call chhena or paneer.

Cheese is also made through the same process and it usually involves making use of rennet, an enzyme in a cow's stomach, to thicken or coagulate milk. Even half and half can cause problems. When heated to boiling, the milk fats clump together and separate from the liquid. Although eating the sauce won't hurt you, a curdled sauce is far from appetizing. To prevent curdling in dairy-based sauces, heat them over medium heat and avoid boiling them.

You can also add a bit of cornstarch to the cold milk. The starch helps stabilize the milk so that the sauce is less likely to curdle. Acidic ingredients, such as vinegar, lemon juice and even wine, can cause a dairy-based sauce to curdle.

Acid causes the proteins in the dairy product to coagulate and separate, so you're left with a clumpy mess. If you're making a substitute for buttermilk, you may want the milk to separate and clump. Otherwise, avoid adding acidic ingredients to a dairy-based sauce or add the ingredient at the end of the cooking time.

Fixing a curdled egg-based sauce is fairly simple. Pour it through a sieve or whisk it vigorously to break down the bits of scrambled eggs.

Unless the sauce is completely curdled, it should be fine. Fixing a dairy-based sauce is a bit trickier. First, heat a small amount of cream or milk in a saucepan. Slowly whisk in the broken sauce and heat it gently. The fat in the milk tempers the sauce and usually restores it. While curdled milk is safe to eat, it is not particularly appetizing. Milk is a mixture called an emulsion of butterfat, proteins, and water.

When milk is boiled, the three components of the emulsion break apart: the milk proteins coagulate and separate from the water, producing what is commonly known as curdled milk. This is how cheese is made. The milk solids are coagulated through cooking, then an enzyme called rennet is added, and then the excess liquid is drained away.

If you ever see drops of oil coming off your melted cheese, that is because of the emulsion breaking. It usually happens because it's a low-moisture variety of cheese. For your sauce or soup, you don't want curdled milk, you want it to be nice and smooth.

Use these tips to help prevent milk from curdling when you heat it. Boiling is a sure way to curdle milk. It's not just boiling. Heating milk too quickly, even if it never comes to a boil, can also curdle it. To prevent the dairy from curdling, heat the milk gently over medium-low heat. Starches like flour or cornstarch help stabilize the milk emulsion. This will prevent it from separating. A common technique is to thicken your sauce or soup with roux before adding the milk. This changes the makeup of the liquid and prevents curdling.

If your sauce or soup contains an acidic ingredient like wine, tomatoes, or lemon juice, the milk is more likely to curdle. To counteract the effect of the acid, you can use a starch along with the acid.