Why is it okay to eat blue cheese, but not other things that are moldy?


Why is it okay to eat blue cheese, but not other things that are moldy?

In: Biology

Different species of mold have make different byproducts as they grow, and not all of them are harmful. Through experience we know some that are safe, like those used in making cheese. (Yeast is also a fungus, but not a mold, and is used for baking and brewing.) When food around the house gets moldy from whatever spores were in the air, it’s a bad bet: there’s a big risk that whatever mold it is either is generally poisonous or might produce something you’re allergic to.

This why cleanliness is actually very important when working with mold. Get the wrong kind of fungus in your product and it will ruin the whole batch.

Just like with bacteria, mold is a very broad term. Some mold is good for you, like penicillin, some mold is bad for you.

Just like how the bacteria on yogurt is good for you, but the bacteria in spoiled milk is bad for you.


Almost all fungus produce various types of mycotoxins, mushroom poisons. They do this because it’s their way of defending themselves from bacteria.

Funnily enough not all mushroom poisons are effective against humans. Humans are quite resistant to a lot of different toxins, like those in chocolate, onions, tea etc etc. Some of the stuff that’s very bad for some of our best friends like cats and dogs. The varieties of Penicillin for example, the mushroom poison in blue cheese, is straight up lethal to guinea pigs. But not to humans, although some have allergic reactions.

It all depends on the capabilities of our livers, the organ that’s primarily responsible for breaking down toxins in our body, and exactly how our cells function inside. Allergic reactions depend on how the immune system identifies threats. Every animal is slightly different in that regard, and some can eat stuff that we would consider poisonous, and to some our every day foods are pure death.

Just as some fruit is good to eat, some is poisonous. We can grow molds that are good for us just as we grow berries and mushrooms that are good for us. We do this carefully, with special equipment, so that the molds we grow in cheeses and yogurt and other similar products, and we are careful to keep everything clean so that we only grow the mold we want.

Blue cheese is made by taking a bit wheel of cheese (various sorts) and sticking a very long syringe full of the specially made (cultured) mold (made liquidy) into the cheese. They squeeze the syringe and pull it out (retract it), so the mold is dispersed within the protein an fat of the cheese. This is done again (repeated) so that the cheese is riddled with mold.

Then, the mold is left to grow inside the cheese. When it is ready (time depends on cheese type) the cheese is cut and people eat it.

Most people are pointing out that the mold in blue cheese is a specific known quantity that we know is safe. While the chances of actually getting sick from moldy food is very low assuming you don’t have an allergy, it is still a possible risk. However, most mold makes food taste absolutely awful. So while the chances of eating moldy bread making you sick are small, you wouldn’t want to eat moldy bread anyway because it is absolutely disgusting tasting.


Something I’m not seeing in many of the comments, that talk about how not all molds are bad…

The mold in blue cheese is actually beneficial. In addition to being nontoxic to human- it prevents other, toxic molds from forming, increasing the lifespan of the cheese.

Soy sauce is the juice from moldy beans. Moldy beans and rice are popular in Asia (miso, doenjang, gochujang, doubanjiang). Sake (and other rice wines) are fermented with a combination of the same mold and yeast, but we wouldn’t call sake “moldy”.

One aspect of your question. It’s actually fine to eat many things that are mouldy (although no guarantee they taste good) but it’s very difficult for a novice to identify dangerous vs harmless mould and there are some extremely poisonous moulds that it could be so it’s generally not worth the risk.


You know how there are different kinds of doggies? And some doggies are nice and let you pet them? The same is true for lots of other things, even mold! Blue cheese mold is like a nice doggie in our tummy – it tastes good to lots of people and doesnt make us sick. Other kinds of mold are like mean doggies though and can taste bad or make our tummys upset. Some mold even helps us feel better when we are sick! We should only try moldy things we already know are yummy or helpful though, just to be safe!

It does vary. I recall my late brother-in-law, during his lactovegetarian phase, going on about how to store rice in bulk and what colors of mold were safe (red, yellow) and unsafe (blue) to eat.