Here is what happens, chemically, when you bake a pizza. (Warning: The following description will be ever-so-slightly disgusting.)
The water molecules contained in the cheese atop the pizza—all those little H2Os, trapped between the protein and the fat—heat up. In fairly short order, the water begins to boil. When that happens, the water becomes steam. But the steam is trapped in the cheese—inside all that protein and fat—so it can't evaporate into the surrounding air. Instead, it pushes against the surface of the cheese. The cheese, in turn, starts to bubble.
So that's what generally happens. What that basic process looks like in practice, though, varies greatly depending on which kind of cheese tops the pizza. If the cheese has more moisture, the bubbles the steam creates will be large. A less elastic cheese will produce smaller bubbles.
And that distinction, in turn, affects what is arguably the best part of a pizza: the cheese's ability to brown in the oven. All that bubbling and steaming causes the oil to leak out of the melting cheese, settling on the surface. Cheese with high moisture content and low fat content will create bubbles large enough to break that surface of oil, exposing the moisture in the bubble directly to the oven's heat—meaning that it evaporates, leaving the rest of the cheese to brown. Only some cheeses produce that effect, though. If a cheese is low-moisture and low-fat, it will burn; if it's high-moisture and high-fat it will simply stay greasy without browning.
All of which helps to explain why, when it comes to pizza, there is one cheese to rule them all—and why that cheese is, greasy hands down, mozzarella. Mozzarella hits that high-moisture, low-fat sweet spot that makes for a bendable, brownable pizza topping. And now, thanks to a team of food scientists at the University of Auckland in New Zealand, we know a bit more about why that is.
The researchers, the BBC reports, developed a high-resolution camera, along with specialized computer software, that are able to measure, with unprecedented precision, the blistering and browning of pizza cheese. They then put various kinds of cheeses to the pizza-topping test—because quantification. Because curiosity. Because science.
The experiment went like this: The team sprinkled grated forms of several different cheeses—cheddar, colby, edam, emmental, gruyere, provolone, and, of course, mozzarella—on pizza crusts and baked them in an oven. (The baking time was the same for each variety, as was, for each experimental "pizza," a lack of sauce.) The team then used its camera to capture the color uniformity of the cheese—browned spots indicating a lack of uniformity—to render an analysis of a cheese's ability to brown. They also subjected the cheese to what the BBC delightfully terms "a standard panel of cheese tests," including measurements of elasticity, moisture content, the amount of oil released as the cheese melts, and the temperature at which it melts.
The team's results, recently published in the Journal of Food Science, confirm that browning, as Bryony James, the the study leader, explains in a video accompanying the paper, "is dictated by a combination of the composition and the mechanical properties of the cheese itself, as well as every other component of the pizza." They also confirm what generations of pizza bakers and pizza enthusiasts have long known: that pizza, in its Platonic Form, is topped with mozzarella. Ooey, gooey, chemically perfect mozzarella.
Via BBC Future
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