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
Sheep milk cheese include Pag cheese and Ovidur. Polish sheep milk cheeses include oscypek and bryndza. Portuguese sheep milk cheeses include Castelo Branco, Azeitão, Rabaçal, Saloio, Serpa and Serra. In Spain is Roncal, made in the Roncal Valley, and is protected by the Protected designation of origin (PDO). Other cheeses from Spain are Torta del Casar and Manchego. Sheep milk cheese Sheep milk cheese is a cheese prepared from sheep milk. Well-known cheeses made from sheep milk include the Feta of Greece, Roquefort of France, Manchego from Spain, the Pecorino Romano and Ricotta of Italy. Yogurts, especially some forms of strained yogurt, may