Why does a milk based cheese sauce curdle when making scalloped potatoes or macaroni and cheese?

There are a few reasons why a milk-based cheese sauce can curdle when making scalloped potatoes or macaroni and cheese.

* Overheating: Milk proteins can start to coagulate and curdle when heated above 180°F (82°C). If you're making a cheese sauce, it's important to heat it slowly and stir constantly to prevent it from overheating.

* Adding cheese too soon: If you add cheese to a milk sauce before it has thickened, the cheese can curdle. This is because the milk proteins haven't had a chance to form a stable structure, and the addition of cheese can disrupt this process.

* Using the wrong type of cheese: Some cheeses are more likely to curdle than others. For example, hard cheeses like Parmesan and cheddar are less likely to curdle than soft cheeses like Brie and Camembert. If you're using a soft cheese, it's important to add it slowly and stir constantly to prevent it from curdling.

* Adding too much cheese: Adding too much cheese can also cause a sauce to curdle. This is because the cheese can crowd the milk proteins and prevent them from forming a stable structure.

* Adding acid: Adding acid to a milk-based sauce can also cause it to curdle. This is because the acid can react with the milk proteins and cause them to coagulate.

If your cheese sauce does curdle, there are a few things you can do to try to fix it.

* Strain the sauce: You can strain the sauce through a fine-mesh sieve to remove any curds.

* Add more liquid: You can add more milk or cream to the sauce to thin it out and reduce the risk of curdling.

* Whisk vigorously: You can whisk the sauce vigorously to try to break up any curds.

* Start over: If all else fails, you can start over and make a new cheese sauce.

Here are some tips for preventing a milk-based cheese sauce from curdling:

* Heat the milk slowly and stir constantly.

* Add the cheese slowly and stir constantly.

* Use a hard cheese that is less likely to curdle.

* Don't add too much cheese.

* Avoid adding acid to the sauce.

* If your sauce does curdle, strain it, add more liquid, or whisk vigorously to try to fix it.