Does Natto Go Bad

In this brief article, we will be discussing the question, “does natto go bad?”. We will also tell you some interesting facts about natto, such as its nutritional value, recommended intake, and proper storage method.  

Does Natto Go Bad?

Yes, natto can go bad. For the best taste, try to use natto within 10 days3 months. However, natto can remain relatively good in taste for as long as a year. A study suggested that storage conditions of 10 days at 5 °C and 5 days at 10°C produced the highest quality natto. During storage, the bacterial number usually does not fluctuate over time, but as the storage period increases, the ammonia and free amino acid content increases while the hardness decreases, which is negative for the overall taste and product acceptance (4).

In short, the longer it is stored, the more apparent are the changes in taste.

How Can You Tell If Natto Has Gone Bad?

When natto goes bad, it will develop tiny white specks. However, these are just amino acid crystals and the product is still edible and safe to consume at this stage, but it won’t be very pleasant-tasting. 

Also, natto that has gone bad will continue to ferment and develop a smell that is slightly off and will also become stickier. The odor of natto is easily intensified due to the progressive production of ammonia, affecting the taste (3).

You can consume natto for up to nine days after its expiration date.

What Is Natto?

Natto is a fermented soybean product. It is widely recognized and consumed as a traditional food in Japan. By steaming soybeans and inoculating with Bacillus subtilis, natto spores to ferment it, and then it would become a characteristic odor, flavor and slimy food. The processing of natto includes soaking, steaming, cooling, inoculating, fermenting and aging (1).

Natto is short for Nattokinase (NK), a powerful protein that dissolves blood clots and is used for treating cardiovascular diseases. The bacterium Bacillus subtilis produces NK during the fermentation of soybeans.

Moreover, the fermentation of soybeans increases their nutritional value and gives natto a distinct sticky texture and flavor. During fermentation the steamed soybeans will produce a large amount of sticky substances which include glutamic acid, fructan, amino acids (such as glutamic acid, phenylalanine, tyrosine) and volatile fatty acids (such as butanediol, ethanoic acid, pentanoic acid) (1). Also, the fermentation process produces the small smell of ammonia which is completely natural. 

Is Natto Healthy?

Yes indeed! Natto is extremely nutritious and a great source of protein – totally worth developing a taste for. Natto contains isoflavones, dietary fiber, vitamins, linoleic acid and some minerals which are originated from soybeans, in addition, it also contains some functional compounds such as enzymes, bioactive peptides, natto kinase (fibrinolytic agent) and gama-polyglutamic acid (2).

Eating natto daily (in recommended amounts) can (2):

  • strengthen the immune system
  • toughen bones
  • provide protection against heart disease 
  • help the body digest foods more easily
  • reduce blood pressure
  • dissolve blood clot
  • prevent against cancer
  • reduce the risk of Alzheimer’s disease

How Much Natto Should You Eat Daily?

You shouldn’t eat more than two packs of natto every day, but it is recommended to keep your daily consumption to one pack (40 to 50 g). However, if you’re REALLY craving natto, a second pack occasionally is not harmful. Japanese average life-span has been the highest for 20 years, reaching 84 on average and this is related to the consumption of natto in every meal (2).

How Can You Make Natto Taste Better?

Ideally, with chopsticks, mix the natto thoroughly inside the bottle. After it becomes sufficiently sticky, you can add some tare and mustard. Mix it again, and enjoy the refined taste. 

The exact taste of natto depends on the batch and the fermentation process. However, its taste has been compared to foie gras, salty cottage cheese, and old Brie. 

Certain people have even compared the taste of natto to resemble that of earthy bacon, although the majority of natto-eaters say they cannot pinpoint a specific or precise flavor for the fermented soybeans. 

Can You Keep Natto In The Fridge?

Natto can be stored in the refrigerator for several months. However, it is a very perishable product and may change its taste in one week. During storage, the odor of natto is easily intensified due to the natural and progressive production of ammonia (3). Natto has a short shelf life because it has a high moisture content of 59.5% (1).

A good tip is to transfer the natto into an airtight container from its jar and press some cheesecloth or unbleached parchment paper over the surface of the container. This prevents moisture from developing inside the container.  

But remember, the longer natto is stored, the more unpleasant its flavor will become.

Can Natto Be Frozen?

Yes. If you want to keep natto fresh well beyond its expiration date, it is recommended that you freeze it as soon as you bring it home. 

A study showed that the vitamin  K2 content in natto was generally 2–4 times higher in frozen products than the content in refrigerated products (5).

When you’re craving to eat it, simply remove the natto from the freezer, transfer it to a microwave-safe container, and heat it for about 40 seconds (500 W). alternatively, you can also defrost it in the fridge overnight, warm it in the morning, and enjoy it.

Frozen natto can be kept for a year or longer, however; it will develop pronounced changes in taste.

How Quickly Does Natto Go Bad?

Natto kept at room temperature will quickly begin to develop mold and lose its flavor, depending on the temperature and moisture. At room temperature, it will deteriorate in one day (3).

Frozen natto should be used within a week after defrosting. However, to enjoy it at its peak flavor, fresh natto must be consumed within four weeks.


In this brief article, we will be discussing the question, “does natto go bad?”. We also told you some interesting facts about natto, such as its nutritional value, recommended intake, and proper storage method.  

If you have any questions or comments please let us know.


  1. Weng, Tien Man, and Ming Tsao Chen. Changes of Protein in Natto (a fermented soybean food) Affected by Fermenting Time. Food sci technol res, 2010, 16, 537-542.
  2. Liu, Yanchun, et al. Analysis of Main Components and Prospects of Natto. Adv Enzyme Res, 2021, 9, 1-9.
  3. Hosoi, Tomohiro, and Kan Kiuchi. Natto–a food made by fermenting cooked soybeans with Bacillus subtilis (natto). Handbook of fermented functional foods, 2003, 227-245.
  4. Kubo, Yuji, Tomotsugu Noguchi, and Keitarou Kimura. Storage temperature and quality changes of natto. Food Sci Technol Res, 2021, 27, 497-504.  
  5. Jeong, IS., Gu, SY., Park, KH. et al. A simultaneous determination and monitoring of vitamin K1 (phylloquinone) and vitamin K2 (menaquinone) in vegetable drinks and natto sold on the Korean market. Food Measure, 2022, 16, 248–257.