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
Stilton cheese three counties of Derbyshire, Leicestershire and Nottinghamshire, and must use pasteurised local milk. The manufacturers of Stilton cheese in these counties applied for and received Protected Geographical Status (PDO) in 1996. Stilton cheese cannot be produced in the village that gave the cheese its name. Stilton village is not in the three permitted counties; it is in the administrative county of Cambridgeshire, and in the historic county of Huntingdonshire. The Original Cheese Company applied to Defra to amend the Stilton PDO to include the village but the application was rejected in 2013. To be called "Blue Stilton", a cheese must: