Before use, a peel is typically sprinkled with cornmeal to allow the pizza to easily slide on and off it. When made at home, a pizza can be baked on a pizza stone in a regular oven to reproduce some of the heating effect of a brick oven. Cooking directly on a metal surface results in too rapid heat transfer to the crust, burning it. Some home chefs use a wood-fired pizza oven, usually installed outdoors. As in restaurants, these are often dome-shaped, as pizza ovens have been for centuries, in order to achieve even heat distribution. Another variation is grilled pizza, in which the pizza is baked directly on a barbecue grill. Greek pizza, like deep dish Chicago and Sicilian style pizza, is baked in a pan rather than directly on the bricks of the pizza oven. Most restaurants use standard and purpose-built pizza preparation tables to assemble their pizzas. Mass production of pizza by chains can be completely automated. Crust The bottom of the pizza, called the "crust", may vary widely according to style – thin as in a typical hand-tossed Neapolitan pizza or thick as in a deep-dish Chicago-style. It is traditionally plain, but may also be seasoned with garlic or herbs, or stuffed with cheese. The outer edge of the pizza is sometimes referred to as the cornicione. Some pizza dough contains sugar, to help its yeast rise and enhance browning of the crust. Dipping sauce specifically for pizza was invented by American pizza chain Papa John's Pizza in 1984 and has since been adopted by some when eating pizza, especially the crust. Cheese Mozzarella cheese is commonly used on pizza, with the buffalo mozzarella produced in the surroundings of Naples. Other cheeses are also used, particularly Italian cheeses including provolone, pecorino romano, ricotta, and scamorza. Less expensive processed cheeses or cheese analogues have been developed for mass-market pizzas to produce desirable qualities like browning, melting, stretchiness, consistent fat and moisture content, and stable shelf life. This quest to create the ideal and economical pizza cheese has involved many studies and experiments analyzing the impact of vegetable oil, manufacturing and culture processes, denatured whey proteins, and other changes in manufacture. In 1997, it was estimated that annual production of pizza cheese was in the U.S. and in Europe. Varieties and styles A great number of pizza varieties exist, defined by the choice of toppings and sometimes