A three-minute video from the series Reactions, hosted by the American Chemical Society, delves into the science of how cheese melts: it all comes down to how casein proteins clump together into spheres called micelles, which are held together by calcium and are full of fat. The surface of a micelle is negatively charged, so usually the little balls would bounce away from each other.
But when lactic acid gets involved, the micelles smack into each other and create chains that trap water and turn into a mess of cheesy goo. Cheeses that age longer contain more lactic acid, lowering its PH. That means sharper cheeses have a lower pH than their counterparts, which don’t age as long.
According to the American Chemical Society’s video, what this all means is that the ideal pH level for a cheese used to make grilled cheese is perfectly balanced between 5.3 to 5.5 (here’s a list [PDF] of PH levels in food). Any lower and cheese will release all its oil when heated, leaving curdled, clumpy clusters.
So what should you choose? Try gouda, gruyére or manchego. If you’re choosing between mild and sharp cheddar, go with mild — it has the texture you want, and won’t break down like its sharp counterpart.
If you want suggestions on how to cook that grilled cheese once you’ve selected which variety you want, check out our somewhat scientific We Tried It investigation.
For more science and cheese and cheese science, check out the video below: