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Does Natto (fermented soy beans) spoil?

  • t

Was wondering if Natto spoils. mine has been in the fridge for 2 months almost and it still looks and tastes fine and I feel fine so I'm guessing the answer is that it doesn't. (I was craving it and had to eat some.) There's no expiration date on the packaging just a very long distance phone number. my japanese isn't that great so I was wondering if anyone out there knew. thanks in advance - tom S.

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  1. I have never used natto, but considering that my bf uses fermented soybeans as bait when fishing for catfish, (and it smells worse than stinkbait) I would say it *could* spoil!! :-)

    1 Reply
    1. re: Katie Nell

      But that's how it smells when you eat it at a restaurant...sort of an aquired taste one might say. So, I don't know if that's an indicator.

    2. Don't know about natto, but I've had fermented black beans in the fridge for maybe four months now and they're just fine. Read somewhere that they'll keep practically indefinitely if refrigerated. Perhaps the same is true of natto?

      1 Reply
      1. re: JoanN

        I believe the Chinese style black beans (as used in black bean sauces) are more heavily salted than natto.

        I have only bought natto frozen in the single serving foam containers. So I keep it in the freezer till I need my natto 'fix'.


      2. TOO LATE...natto's already spoiled!

        I've never known natto to spoil, but my grandmother used to say it got stronger, which probably means it continues to ferment.

        1. i worked for a sushi restaurant...and asked the same question to the itamae...he said a few months is fine...as another poster had replied its spoiled already.

          to be safe keep it in the freezer, which i do until use

          1. I do recall seeing dates on the package, as Ricepad said, I think it's more of a "best by.." date. You can always freeze it if you won't eat it quickly.

            Link: http://virtualfrolic.blogspot.com/

            2 Replies
            1. re: vf

              "Best by" date on natto -- isn't that an oxymoron?

              1. re: Larry

                I think that even if something is fermented to start with, at a certain point, all things kind of get funky. I recall having some gross natto growing up. I think it had been kept too long, so the beans were kind of dried out and shriveled (still stringy), but just not as plump and juicy as they could be.

                Link: http://virtualfrolic.blogspot.com/

            2. If you licked a spoon and put the spoon in the natto it will eventually spoil. The bacteria from your hands or saliva can grow inside the natto container thus mold spores will grow.

              That's why it's always a good idea to use a new spoon when you scoop out any condiments or food.

              1. Natto is like cheese in some ways. It can become ammoniated if left too long, even in the fridge. That's how it spoils. Storing them in the freezer until you consome it is the best way to deal with natto. They will keep indefinitely that way.

                1. I'm on the edge of my seat now. What does natto taste like!?!? Smell like? Is natto the soybeans I'm sometimes served at the beginning of dinner in a Korean-Japanese restaurant with the other condiments? (They said soybeans, when I asked what they were.) Those were sorta crunchy, sorta slippery, and looked like miniature black-eyed peas... the outsides had sort of become a little clear and glassy, almost.

                  4 Replies
                  1. re: Foodie2

                    If you'd been served natto, you'd know it. Natto is fermented soybeans that look..well...spoiled. They're tan/light brown, and have a coating on them that looks as if the world's largest snail crawled over them...slimy, sticky, and stringy. The first time you have them, you're likely to be put off by the smell.

                    It's hard for me to describe the taste and smell, tho. Kinda nutty, kinda cheese-like, I guess. But strong. Very strong.

                    1. re: Foodie2

                      Those black beans are different from natto.

                      Just to give you perspective..even a large amount of Japanese people are put off by the smell and consistency of natto. It's definetly an acquired taste. The smell screams "fermented" (so kind of dirty sock-esque). Keep in mind the smell gets worse once you put it on top of warm rice. The consistency is like nothing else. The coating stretches like mozarella and stretches forever, you have to spin your chopsticks to get it to cut off!

                      I recommend buying maybe a one-pack (not too expensive around a dollar or so) and giving it a try on top of some hot rice. It's one of those, you either love it or hate it.

                      All this talk about natto makes me want to go out and buy some tonight!

                      Link: http://virtualfrolic.blogspot.com/

                      1. re: Foodie2

                        It smells exactlylike what they are--soybeans gone bad. Texture is akin to okra innards. Tastes like chicken; seriously, it tastes like unsalted, nutty edamame.

                        It's cute how the natto containers have holes in them so the natto can breathe.

                        1. re: Foodie2

                          No, it's not the little cooked marinated black beans they serve at Korean restaurants.

                          Natto is roasted ferminted soy beans, the beans are brownish in color and since it's roasted it has a bit of roasted taste in them (very light hint of coffee taste). It is very slimy, more so than the Korean black beans.
                          When it's mixed it looks like mixed warm rice crispy treats. Well, just look at the picture below to get an idea of how slimy it is.

                          Image: http://www.auvelcraft.co.jp/natto/img...

                        2. Go to
                          and scroll down to Vol. 6 Natto.