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
Types of cheese marketed under the same name are made from milk of different animal—feta cheeses, for example, are made from sheep's milk in Greece and from cow's milk elsewhere. Double cream cheeses are soft cheeses of cows' milk enriched with cream so that their fat in dry matter (FDM or FiDM) content is 60–75%; triple cream cheeses are enriched to at least 75%. There are three main categories of cheese in which the presence of mold is an important feature: soft-ripened cheeses, washed-rind cheeses and blue cheeses. Soft-ripened cheeses begin firm and rather chalky in texture, but are aged from the exterior