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
Blue cheese cheese that originated subsequently, such as the 20th century Danablu and Cambozola, were an attempt to fill the demand for Roquefort-style cheeses that were prohibitive due to either cost or politics. Similarly to other varieties of cheese, the process of making blue cheese consists of six standard steps, as well as further additions that give this blue-veined cheese its unique properties. The first step is acidification where a starter culture is added to milk in order to change lactose to lactic acid, thus changing the acidity of the milk and turning it from liquid to solid. The next step is