How chemistry creates the perfect, gooey grilled cheese sandwich

Looking for the best cheese for a gooey grilled sandwich? Try gouda, gruyére or manchego. That’s according to the chemistry video series Reactions, which is hosted by the American Chemical Society. As the 3-minute video explains, these cheeses have the ideal acidity — or pH — for melting into a goopy mess.

Cheese, as you likely know, is made from milk. Milk is composed of 90 percent water, and the remainder is lactose (a sugar), calcium, fats, minerals and proteins like whey and casein. During the cheesemaking process, milk is curdled, removing much of the whey and leaving casein to help define the texture of cheese.

Casein proteins collect into nanosized spheres called micelles, which are held together by calcium and trap fats within their interiors. The surface of micelles is negatively charged, so these balls typically repel each other. However, curdling causes micelles to bump into each other, forming chains that trap water and aggregate into a gel.

Acid makes this clumping possible. Cheese makers added bacteria and enzymes to milk that transform lactose into lactic acid.

Once cheese curds are formed, acid levels dictate the ultimate ‘gooeynees’ of cheese by relaxing the grip that calcium has on micelles. Cheeses with an acidity in the range of pH 5.3-5.5 — such as gouda, gruyére or manchego — make for solid melting, according to the video. Some varieties of roquefort, parmesean and edam fall in this range too.

But too much acidity (or a very low pH) can have an unfortunate consequence. To learn what it is and how to judge the acidity of cheese based on its sharpness, check out the video.