What makes Blue Cheese blue?

Blue cheese gets its distinct blue veins or spots from a type of mold called Penicillium roqueforti. This mold is added to the milk or curd during the cheesemaking process and allowed to grow under controlled conditions. Penicillium roqueforti produces enzymes that break down the cheese's proteins and fats, creating the characteristic flavor and texture of blue cheese. As the mold grows, it also produces a blue or greenish-blue pigment that gives the cheese its distinctive appearance.