cheese used is actual Mozzarella. Provolone is the second most popular one. Cheddar may be mixed with Mozzarella to preserve chewiness. Grated Parmesan may be added to the top of a pizza, and typically does not melt well when cooked. A diverse variety of processed pizza cheeses are produced, including analogue cheese. Provel is one example. Other pizza cheeses include Emmental and Romano; Detroit-style pizza is noted for its use of Wisconsin brick cheese. Ricotta is used for calzones or as a topping. Several cheeses may be mixed together in its formulation, and each has individual browning and blistering characteristics. For example, a combination of Mozzarella and Cheddar may blister less when cooked compared to other combinations, because cheddar has less elasticity, while Mozzarella and provolone may brown less compared to other combinations. Processed pizza cheeses Pasteurized and processed cheese-like products for pizza that are quicker and cheaper to produce than real cheese and designed to melt well and remain chewy are used on many mass-produced pizzas in North America and the United Kingdom. These products are referred to as analogue (or analog) pizza cheese; in the UK the term "cheese analogue" is used, making clear that it is not actually cheese. In the book Technology of Cheesemaking, editors Law and Tamimethat state that analogue pizza cheese appears to be the leading type of cheese analogue produced globally. Each year in the United States, 700 million frozen pizzas are sold, three-quarters of which contain cheese substitutes. Analogue pizza cheeses may be formulated for processing with less sophisticated cheese-making equipment than is required for Mozzarella cheese, such as using simple mixing and molding. They tend to have a soft texture and once melted, may have a slightly "stringy" quality when pulled or bitten into. They may lack in a fusion, or melting together of the shredded product when cooked, in which the cheese gels together. New stabilizer systems have been developed that have helped to enable the creation of analogue pizza cheeses. An example of a processed pizza cheese is Provel, which uses Cheddar, Swiss, and Provolone cheeses as flavorants. Some analogue types are made with casein, a by-product of milk, and vegetable oil, rather than milk fat. Casein-based Mozzarella-like imitation processed cheeses prepared using rennet are also used as a Mozzarella substitute on frozen pizzas. In some instances, the production of analogue pizza cheese can be similar to the production