Pizza cheese encompasses several varieties and types of cheeses and dairy products that are designed and manufactured for use specifically on pizza. These include processed and modified cheese such as mozzarella-like processed cheeses and mozzarella variants. The term can also refer to any type of cheese suitable for use on pizza. The most popular cheeses used in the preparation of pizza are mozzarella (accounting for about 30%), provolone, cheddar and Parmesan. Emmental, Romano and ricotta are often used as toppings, and processed pizza cheeses manufactured specifically for pizza are mass-produced. Some mass-produced pizza cheeses are frozen after manufacturing and shipped frozen. Processed pizza cheese is manufactured to produce optimal qualities in browning, melting, stretchiness and fat and moisture content. Several studies and experiments have analyzed the impact of vegetable oil, manufacturing and culture processes, denatured whey proteins and other changes to create ideal and economical pizza cheeses. In 1997, it was estimated that annual production of pizza cheese products was 2 billion pounds in the United States and 200 million pounds in Europe, and in 2000 demand for the product in Europe was increasing by 8% per year. The trend of steadily-increasing production and consumption of mozzarella and pizza cheese continued into the first decade of the 21st century in the United States. Varieties and types The International Dictionary of Food and Cooking defines pizza cheese as "a soft spun-curd cheese similar to Mozzarella made from cow's milk..." that is "...used particularly for pizzas and contains somewhat less water than real Mozzarella..." Most are at least 95 percent Mozzarella, with different moisture and fat densities. Cheese for frozen pizzas may be comminuted, in which the cheese is processed into minute granules or fragments. Low-moisture Mozzarella can be formulated specifically for pizza. Cheese may be processed into blocks, from which the product can be grated, made into granules or sliced for use on pizza or other foods. Pizza cheese frequently consists of a blend of two or more cheeses, such as low-moisture Mozzarella or Provolone. Low-moisture Mozzarella was first manufactured in dairy factories in the Midwestern United States, and was originally called "pizza cheese". Compared to standard Mozzarella, low-moisture Mozzarella has a firmer texture, is easier to grate, has better browning and melting characteristics, and is less perishable. Globally, Mozzarella is the most popular pizza cheese. However, it has been estimated that in the United States only 30% of all pizza