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 Protetta. Blue cheeses with no protected origin name are designated simply "blue cheese". The main structure of the blue cheese comes from the aggregation of the casein. In milk, casein does not aggregate because of the outer layer of the particle, called the “hairy layer.” The hairy layer consists of κ-casein, which are strings of polypeptides that extend outward from the center of the casein micelle. The entanglement of the hairy layer between casein micelles decreases the entropy of the system because it constrains the micelles, preventing them from spreading out. Curds form, however, due to the function that the