How do you perfect what is already one of the world’s most perfect foods? Add a little chemistry. This week, the American Chemical Society’s video series Reactions explores how to make the optimal grilled cheese. 

Their main advice: Find a cheese with the perfect pH. The longer a cheese is aged, the more lactic acid it has, and thus, the lower the pH. A cheese with a fairly low pH has just the right balance of calcium and proteins and will melt as one gooey substance. But if the pH is too low, as with really sharp cheeses, it will release all its oils as it heats up, becoming a curd-y, oily mess. Ideal grilled cheeses are made with varieties that have pHs between 5.3 and 5.5, such as gruyere, gouda, and Manchego. If you’re shopping for cheddar, a mild type will melt better than a sharp one. The reason American cheese melts so well? It’s got a pretty high pH, at around 5.8. 

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