Buffalo milk differs from cow milk in composition. It carries roughly twice the fat, more protein and more total solids, and it contains no beta-carotene, which is why buffalo mozzarella and butter are white rather than cream-coloured. The higher solids content means a given volume yields substantially more cheese.
The European Union protects mozzarella di bufala campana under a designation of origin that requires milk from water buffalo raised in defined areas of Campania and neighbouring provinces. Cheese sold simply as mozzarella in most markets is made from cow milk and is a different product, a distinction routinely blurred on menus.
The herds behind it are river-type water buffalo, the South Asian lineage that was brought to Italy centuries ago. They are the same species as the swamp buffalo of Southeast Asia used chiefly for draught work, but the two types differ in chromosome number, with river buffalo carrying fifty and swamp buffalo forty-eight; they interbreed and produce fertile offspring nonetheless.