The processed cheese blend typical on St. Louis-style pizza is Provel.
Provel is a white processed cheese product closely associated with St. Louis cuisine and traditionally used on St. Louis-style pizza. It is formulated from cheddar, Swiss and provolone, with liquid smoke commonly listed among its ingredients. The blend has a low melting point, a smooth texture and a distinctive buttery, slightly smoky character.
St. Louis-style pizza developed its own identity through more than its cheese. It typically has an unleavened, cracker-like thin crust, a somewhat sweet tomato sauce and toppings cut into small squares rather than triangular slices. Provel melts into a cohesive layer instead of behaving like the stretchy mozzarella common on many other American pizzas.
The product was developed in the St. Louis area in the mid-20th century, reportedly through work involving Costa Grocery and a Wisconsin dairy. It is sometimes mistaken for Velveeta because both are processed cheeses, but Velveeta is not the characteristic cheese of this regional pizza style.