What makes blue cheese blue?

What makes blue cheese blue? The signature blue or green veining on these types of cheeses come from the addition of Penicillium mold during the cheesemaking process. The most typical blue mold used is called Penicillium Roqueforti, named after a village in southern France where the discovery of the mold originated. Another mold used in cheesemaking is Penicillium Glaucum, which produces a greenish vein coloring in a cheese.

These Penicillium molds cannot grow without oxygen, so cheesemakers pierce holes into the wheels of cheese during aging. The blue or green veins start to grow in the air pockets left behind by the piercing tool. The mold is what gives blue cheese it’s distinct odor, color, and flavors!