Good cured ham depends above all on three factors for its quality: the pigs from which it is produced, the skills of the artisans who process it, and—perhaps most important—the air that dries it. Prosciutto di Parma is made from two breeds of pig, Landrace and Suino Tipico Italiano, long-legged, with particularly meaty hindquarters and enough fat to ensure a long, slow drying period that won't shrivel them into inedible hardness. These pigs feed only on grain corn and, in an age-old marriage of agricultural convenience, some of the whey left over from the production of parmigiano-reggiano. According to rules established in 1963 by the Consorzio del Prosciutto di Parma, which represents the producers of this special ham, pigs destined to be turned into prosciutto di Parma can be raised in Lombardy, Piedmont, and the Veneto as well as in Emilia-Romagna. Typically, they are slaughtered near where they are raised, at an age of 10 to 12 months and a weight of at least 140 kilos (308 pounds). Wherever the hams come from, they must be cured in the province of Parma, in facilities belonging to members of the consorzio.