How Blue Cheese Actually Gets Its Signature Color

Blue cheese is something that you pretty much know when you see it. It is generally marked with characteristic blue-hued veins running throughout the otherwise white or yellow cheese — though the color in your "blue" cheese can also be green, yellow, pink, or white. And if you didn't know blue cheese was safe to eat, you'd probably swear it was a moldy old mess and toss it in the trash. But blue cheeses are beloved by millions of people all over the world. Ranging in flavor and pungency, every blue cheese gets its color from a mold called penicillium, which is typically introduced into the cheese early in the production process. Several strains of this mold are used, with each resulting in different flavors and colors. (For the record, penicillium is also used to make the medicine penicillin, but the antibiotic comes from an altogether different strain of fungus.)

Once wheels of cheese are formed, they are pierced and injected with mold. These piercings also introduce the penicillium to air, which helps it to grow and spread throughout the cheese. But it is not just the mold in blue cheese that flavors it. It starts with the kind of milk the cheese is made of, which can be from cows, buffalo, goats, or sheep. Other factors that make each type of blue cheese different and special include whether the milk is raw or pasteurized, the diet of the milked animal, and the aging process of the cheese.

Of course, there is a huge difference between cheeses that are meant to be blue and those that turn blue in your refrigerator because they've sat for too long. A little mold won't spoil a block of harder cheese, as you can safely cut off a little growth, but it's better to toss the whole thing if you're dealing with soft or pre-sliced cheeses. But this does raise the dilemma of how to know if your blue cheese has gone bad – it's not like you can judge its freshness based on the presence of mold.

Blue cheese aficionados can use their experience and know-how to determine if a blue cheese tastes or smells off, but novices may not be as well versed in this area. Some telltale signs of blue cheese truly going bad include the presence of furry, fuzzy mold on the surface, a texture that is either slimy or dry and brittle, or an odor that's more akin to ammonia or sour milk. Patches of pink or yellow coloring could also be a sign that a blue cheese is past its prime.

A fresh wedge of blue cheese, however, can be a delight to eat, and certainly adds color and interest to a cheese board. Aside from enjoying it with crackers, fruit, and wine, blue cheese can also give bland meatloaf a new life, add a spark to salads, and cool off a platter of Buffalo wings.