Cheese begins to melt at 90 degrees Fahrenheit. At this point, the milk fat melts and the cheese becomes very soft. The temperatures necessary for the rest of the melting process depend on the specific type of cheese and its moisture content. Some cheeses do not melt at any temperature.
The melting cheeses include Cheddar, Swiss, Pecorino Romano, Mozzarella and Parmesan. As these cheeses pass 90 degrees, they soften and exude tiny milkfat globules. They do not fully melt until the heat breaks down their protein matrix. The softer the cheese, the more readily its proteins break down. For example, soft mozzarella enters this stage at 130 degrees, while Swiss and Cheddar must pass 150 degrees. Hard cheeses such as Parmesan and Pecorino Romano do not fully melt until their temperature exceeds 180 degrees.
Melting cheeses are cured by rennet, but cheeses produced by acid curdling never melt. Non-melting cheeses include fresh Indian panir, goat cheese, halloumi, ricotta and Latin queso blanco. When heated, these cheeses release their water and grow progressively drier and harder. Heat produces a chemical reaction within non-melting cheeses and causes them to jettison water molecules. As the water boils and evaporates, the remaining cheese becomes firmer and assumes an increasingly toothsome texture.