Mozzarella is commonly used cheese on pizza, with the highest quality buffalo mozzarella produced in the surroundings of Naples. Today, other cheeses have been used as pizza ingredients (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 1,100,000 tons in the U.S. and 110,000 tons in Europe.