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Recently, I bought two pieces of cheese - St. Agur and Pyrenean cheese. They were cut from wheels, not pre-packaged. At home, I removed the foil and placed them in the same plastic container in the fridge.

Two days later, the Pyrenean cheese had some mold with bluish tinge on the surface. I assume the seller has stored the cheese properly, so it shouldn't have gone moldy by itself in the short time in my fridge. I think that the benign mold from the blue cheese colonized the Pyrenean cheese. Still, I decided not to risk eating it (I still ate the blue cheese).

Is this what really happened? If it happens again, can I assume that it is edible mold? Is it safe to eat edible mold after it has colonized another type of cheese, or will the changed food prompt it to produce dangerous byproducts?

Also, could I have prevented it by having the cheeses individually wrapped in foil inside the same container, or would only keeping in different containers stop mold propagation?

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    Additional question: would it taste good?
    – Cascabel ♦
    Commented Jan 13, 2012 at 18:26
  • Putting cheese in a plastic container really isn't a good way to store it. See my answer to another question here for a better way to store it. The humid environment (from a sealed plastic container) encourage mold growth.
    – derobert
    Commented Jan 13, 2012 at 22:22

2 Answers 2

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Well, first off, mold grows from spores, and your Pyrenean cheese was likely already "contaminated" with Penicillium roqueforti, Penicillium glaucum, and Penicillium candidum spores at the cheese shop (it'd be surprising if the cheese shop isn't covered with them!). So, if you keep it in a environment habitable to them, they will grow. I suspect that you'd get the same results even if you put them in two different plastic containers.

As to its safety, if it was indeed one of the used-in-food Penicillium molds, it should be safe to eat—you can make sheep's milk blue cheeses (e.g., roquefort) after all. But the problem is that the same humid environment that encouraged the Penicillium colonization also encourage other molds—many of which you don't want to eat. Also, I'm pretty sure there are blue-green molds you don't want to eat.

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    You can create amazing things with that mold. Incubating a walnut size chunk of blue with some cream for a couple days creates a lovely tasty thick blue liquid. The stuff has a fancy french name, but it's been too many years since I actually saw the recipe. Here's a ittle piece on propagation: cheeseforum.org/forum/index.php?topic=1562.0
    – Wayfaring Stranger
    Commented Jan 13, 2012 at 23:53
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    Hmmm. I've never encountered a blue mold which would grow on cheese which was unsafe. Orange or yellow is bad news, but blue is pretty much always penicillium.
    – FuzzyChef
    Commented Jan 14, 2012 at 7:14
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    @FuzzyChef: I'm not sure if any of them grow on cheese. Wasn't able to find out through some Googling... but there are certainly ones that grow on other foods (e.g., Penicillium expansum on apples is not a good idea to eat). No idea if they can survive on cheese.
    – derobert
    Commented Jan 14, 2012 at 17:51
  • @WayfaringStranger: Jefromi wants to know more cooking.stackexchange.com/q/20433/160
    – derobert
    Commented Jan 14, 2012 at 18:04
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Even if your Pyrenean cheese wasn’t contaminated in the shop, you put it in a closed vessel (so high humidity environment) with blue cheese, both unwrapped. That would be more than enough to seed the pyrenean cheese with the blue mold from the St. Agur, and it will be happy to grow.

While that mold is safe to eat (I'd have no problem with it), you might not want the taste of the blue cheese in your Pyrenean.

(By the way, while Penicillium roqueforti and similar molds are safe when growing on cheese, they are not safe when growing on e.g. bread!)

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