If you've ever had a slice of pepperoni pizza and wondered why the pepperoni curled, you're certainly not alone. Three main hypotheses attempt to explain this phenomenon and reveal answers that make for a surprisingly simple explanation when put to the test.

The first hypothesis is that the thickness of the pepperoni slice makes a difference, as the top of a pepperoni pizza is exposed to the oven's air, making it cook faster and shrink more. This effect is more pronounced with a thicker pepperoni slice because there's more food between the top and bottom of the pizza, causing it to curl more when the slice of pepperoni is thicker.

The second hypothesis has to do with the type of casing that the pepperoni was put into, which can be either natural, collagen, or casing-free. When pepperoni is stripped of its casing before it's cooked, the pepperoni will lie flat, but pepperoni with the casing still on will shrink as it cooks and causes the edges to curl.

The third explanation is that the collagen casing doesn't stretch as much as the fiber casing, and the moisture retention of the meat being forced down to the center and sticking to the sides of the slice affects the curl pattern. This downward "meat flow" of meat and fat in the pepperoni would cause pieces to curl more with collagen casing than with natural casing (per Meat+Poultry).

When these three hypotheses were put to the test, the results revealed that hypotheses one and three affected how the pepperoni curled. However, hypothesis two didn't hold much water, as whether or not the pepperoni casing is removed before you pop the pizza in the oven doesn’t seem to make any difference.