From what I can remember, isn't this: (Regenerated Collagen Casing) responsible for the cupping, I know this has been discussed before.
from the glossary at PM.com
PEPPERONI: In the U.S., pepperoni refers to a spicy Italian-American variety of dry salami made of pork and beef. Pepperoni is a descendant of the spicy salamis of Italy, such as salsiccia Napoletana piccante, a spicy dry pork sausage from Naples. Pepperoni is frequently used as a pizza topping in American-style pizzerias. It is the most popular pizza topping in North America, present on at least 30% of all pizzas. For pepperoni that "cups" and chars when cooked, choose a brand with a collagen casing.