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Any way you slice it, Americans are obsessed with pizza. One in eight of us are noshing it on any given day, according to the U.S. Department of Agriculture. And the average American consumes pizza about 39 times a year, according to the NPD Group, a market research firm.
The signature of a great American-style pizza is not the toppings du jour but the cheese: hot, gooey mozzarella, with big, dark splotches of caramelization.
Pizzerias didn't happen upon that winning recipe by coincidence. Food scientists have been studying and finessing the low-moisture part-skim mozzarella we now put on most of our pizzas for decades. Pizza companies fighting for consumers' loyalty are especially invested in such work.
But a few researchers are interested in studying the chemical and physical properties of pizza simply for the sake of science. Bryony James, a professor of materials engineering at the University of Auckland in New Zealand, is one of them.
It's been known for a while that mozzarella melts and blisters better than most other cheeses. But James and some colleagues wanted to investigate further: Why do different cheeses look and taste different when they're baked? Their paper, titled "Quantification of Pizza Baking Properties of Different Cheeses, and Their Correlation with Cheese Functionality," appears in the August issue of the Journal of Food Science.
The researchers started by cooking up a bunch of pies using various cheeses, including mozzarella, cheddar, Edam and Gruyere, as James explains in a video. Then, they analyzed the pizzas using cameras and special software designed to precisely measure the amount of browning, blistering and oil content.
To further tease out the physical properties of the cheeses, the researchers measured water content and elasticity. They also developed detailed diagrams of what happens to each cheese as it bakes.
The unique browning patterns on mozzarella come from the way it bubbles, James says. Since it's made by repeatedly stretching and molding fresh curds, "mozzarella has a lot of elasticity," she explains. "If you look at it under a microscope, you see it has these channels of fat surrounded by protein."
In the oven, the water in the cheese evaporates to create of steam, which causes it to bubble. Since mozzarella is so stretchy, the bubbles can expand and become fairly big. As the bubbles grow, the oil sitting on top slides off and the exposed mozzarella starts to brown. "Finally, the bubbles pop and recede back down," James says.
Cheddar isn't very elastic, so it barely bubbles, the study found. Yet a cheddar pizza will bake to an even, golden brown.In contrast, Gruyere bubbles really well but barely browns. It's a lot more oily than mozzarella, and the fat keeps the moisture in the cheese from evaporating.
"As a home consumer, you might want play around with these things," James says. Want a pizza with the traditional blistering, but sharper flavor? Try mixing mozzarella with another cheese.
Eventually, James says, the sort of research she's doing could be used to manipulate the properties of foods, like a low-fat cheese that tastes and looks just as good as the fattier stuff. Or maybe food scientists will figure out how to make a pizza crust that stays crisp, even after a day in the fridge. "When we understand food right down to its micro-structural level," she says, "it gives us the levers we need to change the way it behaves."
We'll raise a slice to that.