Cheese straight from the refrigerator is pretty good, but cheese melted over a hamburger, hot dog, pizza, or inside a grilled cheese is awesome. That is, if it melts correctly. Some cheeses just don’t, or the results aren’t what you expected. Serious Eats explains melting cheese in detail, starting with the chemical bonds that make cheese what it is, followed by the chemistry of cheese falling apart in your favorite recipe.
Technically speaking, cheese is an emulsion of dairy fat and water, held together by a network of proteins. In cooler temperatures, that dairy fat remains a solid; let it warm to around 90°F and the fat reaches a liquid state and the cheese becomes more pliable—you may even notice some cheeses begin to bead with "sweat" if they're left out at room temperature. Raise the temperature by another 40 to 90 degrees and all the bonds that joined your caseins together start to break, allowing the entire protein structure to sag and stretch into an increasingly loosey goosey, lava-like puddle.
What determines a good melting cheese from a bad one has a lot to do with how well it can maintain its emulsion when that protein network begins to collapse, which in turn has to do with the ratio of water to fat, as well as the strength of that protein network.
The easiest way to make sure your cheese melts perfectly is to select the right cheese. But there are ways to make some poorly-melting cheeses work for you, too. When you understand how it all works, you can go crazy creating your own cheese recipes. -via the Presurfer
(Image credit: Vicky Wasik)