Blue cheese of blue veins. The distinctive flavor and aroma of blue cheese arises from methyl ketones (including 2-pentanone, 2-heptanone, and 2-nonanone) which are a metabolic product of "Penicillium roqueforti". These compounds are not formed in other types of cheese fermented by bacterial acidification alone. In the European Union, many blue cheeses, such as Cabrales, Danablu, Gorgonzola, Roquefort and Blue Stilton, carry a protected designation of origin, meaning they can bear the name only if they have been made in a particular region. Similarly, individual countries have protections of their own such as France's Appellation d'Origine Contrôlée and Italy's Denominazione di Origine
American cheese American cheese was often simply called "yellow cheese". Today’s American cheese is, by law, required to be manufactured from at least two types of cheese. Because its manufacturing process differs from "unprocessed" traditional cheeses, American cheese cannot be legally sold under the name (authentic) "cheese" in the US. Instead, federal laws mandate that it be labeled as "processed cheese" if simply made from combining more than one cheese, or "cheese food" if dairy ingredients such as cream, milk, skim milk, buttermilk, cheese whey, or albumin from cheese whey are added. As a result, sometimes even the "word" "cheese" is absent