We have a jar of sweet miso that has been in our fridge for several months. I know that miso keeps practically forever, and that is naturally fermented. But I was surprised to find when I opened it that a layer of mold had formed at the top.

If I scrape off the top layer and discard it, is the rest of the miso safe to use? Or do I need to toss the whole jar?

2 Answers 2


The mold is the indication that the content is compromised with substances that the mold can grow on or with mold that does not mind the environment. This will happen for example when you use a spoon that is not clean. Unfortunately, there is no way to know if this substance is only on the top of the miso. So, whatever it was that the mold grew on, could be in lower layers, too, where non-visible mold with non-detectable toxins could have developed.

So, while a lot of food stuff lasts nearly forever, this is only true while it is uncompromised and proper hygiene is followed.

So, my recommendation would be to toss the whole jar and learn from the experience and not treat fermented food as invincible and reconsider package sizes.


are you sure it is mold. i was asking because i saw a white layer almost from soapy layer on my unopened miso. Through the plastic. It was not smelly I checked online and it says in exception warm condition it developes this layer of same bacteria that is used to ferment miso. If it has grown like proper mold like how you see on bread then you not only need to throw it out. You need to disinect your refrigeration it could be having mold spores in it. You need to clean it with bleach and then spray it down with vinegar and alcohol solution and then with 6% hydrogen peroxide solution. Refrigerator can get contaminated with mold through organic vegatables. I remember bread started catching mold in my fridge after I did this it stopped. I found black mold spots in my vegetable basket and the back side of it.

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