What you see: Your blue cheese seems to have developed fuzzy mold, beyond the blue areas you expected.
What it is: More mold!
Eat or toss: We’re calling this a toss (into the compost, ideally!). But it’s unlikely to be a significant food safety issue.
Is it safe to eat blue cheese that developed more mold?
So, we know that blue cheese is blue because of mold that’s supposed to be there. We also know that while blue cheese is somehow OK, we’re generally advised against eating moldy food. So what is one to do when the food that’s supposed to be a little moldy gets a lot moldy? Like, say, these blue cheese crumbles that are definitely fuzzier than they were when I first opened this little plastic tub.
First, the official word from the United States Department of Agriculture is that unidentified bonus mold on blue cheeses should not be eaten. As we’ve discussed in previous posts, some molds produce toxins that you don’t want to consume. Many molds, like Penicillium roqueforti, which transforms milk fats into the rich flavors of blue cheese, are normally safe to eat. Still, as average consumers we’re not equipped to tell the difference between the edible and not-safe-to-consume molds.
But Nicole Martin, associate director of the Milk Quality Improvement Program at Cornell University, is not an average consumer. She studies the microbes in dairy products and when I showed her an image of this cheese tub turned petri dish, she had this to say:
“It looks unappealing. So, you know, never eat something that looks unappealing. But it’s probably just the same mold that was inside the cheese.”
Martin said that an extended stay in my fridge and/or too much time at warmer temperatures could have caused the standard blue cheese mold to “get out of control.”
I found this fascinating and puzzling. If it was in fact the same mold, why wasn’t it blue, like the original cheese? And why was it fuzzy when the original crumbles were smooth? And does all this mean that the mold used to make the cheese was still alive?
Blue cheese mold is still alive
So, yes, the mold is still alive. When cheesemakers finish a batch of blue cheese, they don’t pasteurize or otherwise process it to kill the cheese-making mold, Martin told me. Instead, the cheese is kept cold and packaged to stall further mold growth.
So, while the mold is still alive, it’s unlikely to grow if the cheese is consumed relatively quickly.
But the blue cheese crumbles we’re discussing today were not consumed quickly. After the package was opened and then sat in my fridge for who knows how long, the time, plus the available oxygen in the air probably inspired our friend Penicillium roqeuforti to grow by sprouting some delicate white threads known in mold speak as hyphae.
Which brings us to the question of the fuzz. Blue cheese has those nice blue ribbons, but isn’t exactly fuzzy. In this case, Martin pointed out that the blue channels in the cheese are dense bundles of mold. But when the mold is growing in a more open environment, the hyphae are more diffuse and look fuzzier. Here are some images of various strains of Penicillium roqueforti growing in a lab. You see several examples of the outer ring sporting a white fuzz just like what I saw on those crumbles.
All of this doesn’t rule out the possibility that there’s another type of mold present, it’s just unlikely. Also unlikely: any kind of bacteria contamination that could sicken you.
“I think that what we’ve seen from real life,” Martin said, is that “there’s virtually no instances of foodborne outbreaks from this kind of a situation.”
Martin said she had her own encounter with extra moldy blue cheese crumbles and opted to throw them away.
“I had that little thing of blue cheese crumbles in the back of my fridge that I forgot was there,” she said. “I didn’t eat it because it just was not appealing to me. But I’m guessing if you ate one it would probably taste like blue cheese.”
- Nicole Martin. Associate Director, Milk Quality Improvement Program. Cornell University. College of Agriculture and Life Sciences.
- Microbes 101. Cheese Science Toolkit.
- Penicillium Mold. Cheese Science Toolkit.
- Penicillium. Britannica.
- Insights into Penicillium roqueforti Morphological and Genetic Diversity. Guillaume Gillot,Jean-Luc Jany,Monika Coton,Gaétan Le Floch,Stella Debaets,Jeanne Ropars,Manuela López-Villavicencio,Joëlle Dupont,Antoine Branca,Tatiana Giraud,Emmanuel Coton. PLOS ONE. June 19, 2015.