why, when cooking a pizza, mozzarella melts but bread gets harder? What makes them react different to heat?
In: Chemistry
It’s not that the bread gets harder, it’s that yeast causes the dough to rise and become bread. If heating continues, the bread becomes dry and then brittle.
Mozzarella, lacking rising agents, and also full of water, melts when the water is released.
One simple explanation is that the fat content of the cheese far exceeds the moisture in the raw dough. Fat doesn’t really evaporate like water does in the dough.
Every fat has a melting temperature. You may have noticed that coconut oil is solid at room temperature but melts if you scoop it into your hand. Olive oil is solid in a refrigerated salad dressing but liquid at room temp. Dairy fats in cheese melt under oven temperatures. As well, the heat breaks chemical bonds in the proteins of the cheese. Without the protein framework, the cheese loses what was holding it together in solid form.
Bread gets crispy primarily because moisture cooks out. That moisture came from water that was added to flour to form the original dough. Bread contains no to little fat. When it does have fat in it, it tends to be olive oil that was liquid at room temperature anyway. Unlike the proteins in dairy (casein), the protein in bread flour (gluten) does not break down until very high temperatures, around 260° C/500° F.
There are many reasons, but one is that water evaporates from the dough, while the fat in the cheese turns liquid. Cheese contains fat and water. If you cook cheese long enough, the fat will seperate and ooze out, and the water will evaporate, and it will be crispy and hard too.
Bread has a higher melting point than mozzarella. It’ll caramelize, and then burn, before it melts.
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