Moldy cheese?

What you see: Moldy cheese.
What it is: Moldy cheese!
Eat or toss: Discard soft cheese with any amount of mold. A small amount of mold on a hard cheese can be cut off with one-inch margins. A hard cheese that’s been truly overtaken by mold, like the one pictured here, isn’t worth saving. 

Can you eat moldy cheese?

Mold is alive, and when it shows up on your cheese, it’s doing what you meant to do: eat the cheese. It does this by basically unleashing a special cocktail of chemicals that help it break down the cheese, much as our stomachs would, and then absorbing the now-more-accessible nutrients through its branching network of filaments. This, of course, is also how some of our fungi friends help us create cheeses like Camembert and Gorgonzola. So if your cheese is moldy, but the mold is supposed to be there, of course you can eat it.

But when uninvited mold shows up on your cheese, it’s impossible to know what chemicals it’s been depositing into your food. Many of them could be harmless. Some could make the cheese taste bad. And others might not be good for your body. Not all molds produce toxins, but among those that do, their toxins range from those that cause fast-onset issues to those that are carcinogenic or just generally not something you want to ingest. And, for sensitive folks, any mold spores you launch into the air when you handle a moldy food could trigger an allergic reaction if they’re inhaled.

So, if you’ve eaten moldy cheese, or moldy anything, and nothing happened, you can’t conclude that it hasn’t done you any harm simply because you had no gastrointestinal distress in the following 24 hours. That said, many molds don’t contain toxins. So, if you accidentally ate mold, don’t stress too much, but maybe just be more careful next time?

Moldy hard cheese: cut off with 1-inch margins

The official guidance from the U.S. Department of Agriculture for mold on hard cheeses is this: cut off small pieces of mold with a one-inch margin. That inch is a safety buffer for the mold chemicals unleashed into the cheese. (Here’s a study that tested how far mycotoxins, that is, the toxins produced by mold, could travel within three-month old cheddar cheese. Researchers didn’t find mycotoxins more than at 1.3 centimeters below the the mold.) 

And, of course, if a piece of hard cheese is as covered as the one at the top of this post, it’s not worth salvaging. Even handling it to trim off those moldy sections could release a number of mold spores in the air—not the best for those with sensitive respiratory systems and also not the best if you don’t want those spores to land on other susceptible foods in your kitchen. 

Moldy soft cheese: discard

Because it’s easier for mold filaments and their chemical cocktails to travel through soft, moist foods, the USDA guidance for mold on soft cheeses is more straightforward: pitch the entire thing. Compost, ideally. 

If a cheese has a green blue mold, is that the same mold as in blue cheese?

Not so fast. Blue cheeses like Gorgonzola, Stilton and Roquefort get their distinctive color from Penicillium roqueforti mold. This is, of course, related to, but still significantly different from the Penicillium mold that gives us the antibiotic penicillin.  Beyond cheesemaking and medicine producing molds, still other Penicillium types, also with a blueish green hue, could colonize your cheese, leaving behind who knows what. On top of that, a fungus that might perform culinary wonders in one cheese, could leave a trail of off flavors and textures in another, as authors John I. Pitt and Ailsa D. Hocking note in Fungi and Food Spoilage. For example, they write that several species of yeast “are common on the surface of St. Nectaire, Camembert and blue-veined cheeses and may play an important role in the development of texture and flavor of these products… However, when present in Cheddar and Gouda cheese, such yeasts can cause taints and off flavours due to their lipolytic and proteolytic activities, and the production of bitter compounds from lactose fermentation.” (“Lipolytic” and “proteolytic” refer to the breakdown of fats and proteins, respectively.)

What if you aren’t sure if your cheese is moldy?

Certain natural and harmless features, especially in hard, aged cheeses, can look a little like white molds. Check out this article to learn about tyrosine crystals—those dots you see in aged Italian and gouda cheeses. This article talks about calcium lactate, which can form a crust on the surface of cheese. And this article provides tips for telling the difference between mold and harmless cheese quirks.