Why does nacho cheese and sausage curdle after reheating?

Nacho cheese is prone to curdling because of the protein content in the cheese. When cheese is heated, the proteins break down and form new bonds with other molecules, causing the cheese to thicken and become stringy. This process is called denaturation. Overheating the cheese can cause the proteins to break down too much, leading to the formation of a curdled, grainy texture.

Additionally, the reheating process can cause the fat in the cheese to separate, resulting in a greasy or oily consistency.

Sausage:

Sausage is made from ground meat, which contains protein and fat. When sausage is reheated, the proteins and fat can separate, causing the sausage to become dry and crumbly. This is especially true for precooked sausage, which has already been partially cooked and may be more susceptible to overcooking.

To avoid curdling or drying out, it's important to reheat nacho cheese and sausage carefully at a low temperature. You can reheat nacho cheese in a microwave or on the stovetop over low heat, stirring continuously to prevent overheating. For sausage, reheating in a pan over low heat, covered, is recommended to prevent drying. Additionally, you can add a small amount of liquid to the nacho cheese or sausage to help prevent curdling or dryness.