I received a text from my sister a few weeks ago, asking me about cheese. I consider this a good thing, because I love cheese nearly as much as I love new science questions. I mean, who doesn’t love cheese? I’m pretty sure the answer is no-one. Anyway, the question Emma asked me was about melting cheese, which is possibly even better than just normal cheese, all gooey and melty and tasty and delicious…. Ahem. Sorry, lost myself there. What she wanted to know was what makes different cheeses melt differently, so for example why does melting camembert or brie produce a consistency that can be spread with ease, or dipped into, while mozzarella produces a stringier texture that streeeetches out? Why does cheddar melt into a consistency somewhere between the two, it can be spread on toast, but will stretch slightly when you bite it. What’s the crucial difference between these cheeses that affects the melt?
I wish I could say that in order to answer this question I needed to carry out extensive research by eating and analysing many cheese samples. Sadly, no such luck, the answer is already out there. That said, all this talk of melting cheese may result in me failing the ‘walk past the amazing-looking cheese shop on my way home from work’ willpower test…
When cheese melts, what’s actually happening is a two-stage process. First, the fat molecules melt from solid to liquid; this can happen at fairly low temperatures and sometimes results in visible beads of melted fat on the surface of the cheese. I think we’ve all accidentally left cheese on the kitchen side in the summer and seen THAT phenomenon. Unless the rest of you are efficient types who put cheese away when they’re done using it. I’m usually too busy eating what I made with the cheese to deal with the remaining cheese on the side. Anyway, that’s stage one; fat beading.
Stage two is when the casein proteins get involved, and things really start to heat up. What happens is that increasing the temperature causes the bonds holding the protein structure together to shake, and shimmy, and generally party so hard that they break free from their nice ordered position, wave their arms in the air and act like they just don’t care. Once the bonds begin to break, the structure of the cheese sort of… gives up. It collapses into a thick, gloopy, melted pile of deliciousness. It’s a party that ends with melted cheese everywhere, which is clearly the best kind of party.
So that’s how cheese melts, however, that still doesn’t explain why not all cheeses melt the same. For starters not all cheeses melt at the same temperature; softer cheeses melt faster and at lower temperatures than hard cheeses. What decides the melting point of a cheese is the water content; drippy wet soft cheeses, which contain lots of water, have proteins that are quite dilute, the volume of water means that the proteins cannot bind together so tightly, and it takes less heat to break their bonds and get them partying. On the other hand, a rock-hard tough cheese like Parmesan, the Terminator of cheeses, has dense proteins, tightly packed and holding on tightly. It takes a lot of heat to get the Terminator partying. And even when the protein molecules do break down and have a little boogie, they don’t really let it all out and sag like an uninhibited Brie, they still remain relatively sedate and confined.
That’s why some cheeses melt to a dippy goo, but why do some other cheeses go stringy? The stringiness comes when the casein molecules are still mostly intact, they haven’t quite given way to urge to dance like no-one is watching. Instead, they are linked together by calcium molecules. In my mind, the calcium molecules help the casein to form a conga line, so that rather than dancing loosely and flowing freely, they stick together in long chains that stretch out and bump into one another on the dance floor. The level of conga formation depends on the conditions under which the cheese was made; for example a high level of acidity means that there is less calcium hanging around. Cheeses in this case are less stringy, and more gloopy.
So, there you go. Melted cheese is just one big dance party. And if any one of you doesn’t feel an overwhelming urge to eat cheese on toast right now… you’re stronger people than me.