According to the video, there's a reason why not just any cheese will work in your favorite sandwich. Melty, gooey cheese is ideal for a grilled cheese, and that involves using a cheese that has a proper pH level. A pH level measures the acidity of the cheese, and it varies depending on how long a cheese is aged. The longer a cheese ages, the more lactose will convert to lactic acid, which will lower the pH. The lower the pH level of the cheese, the easier it is for the bonds to break apart in the cheese - but you don't want to use cheese that has too low of a pH. If that's the case, the cheese will simply bubble within the sandwich, creating a grilled disaster.
According to the video, there's an ideal pH range for the cheese inside your sandwich, and it's between 5.3 and 5.5. You know how you see gouda grilled cheese on every menu everywhere? Well, that's because gouda (as well as manchego and gruyere) fits perfectly into that range.
If you're wondering about the pH level of those classic slices of American cheese, there's a reason why they work so perfectly between two slices of bread. American cheese has an exceptionally good pH level because added phosphate salts limit the amount of calcium holding everything together, raising the pH level while giving it that melty, gooey consistency.
You can check out the entire video below to get schooled on the science behind the ultimate comfort food. Then, head to the stove and grill up some deliciously balanced cheese: