Most cheeses aren't very good at melting and you have to resort to a processed cheese food product like Velveeta for your nachos, cheesesteak sandwiches, etc. Culinary weblog Chow reports that adding a pinch of sodium citrate will keep your cheese from separating so you can enjoy good quality melty cheese.

Sodium citrate (citrus salts) is a product made from citrus fruit and is commonly used in citrus-flavored beverages, ice cream, and oral rehydration salts. It can be hard to find but you can buy a pound of it from Amazon.

Dissolve a teaspoon of so of sodium citrate in a liquid—you can use water, but the Chow expert recommends beer. Grate your cheese and slowly melt it into your sodium citrate solution over medium heat and you'll have perfect melty cheese.

High-Tech Melty Cheese | CHOW Tips