What is Fresh Natto?

Natto (納豆) is a superfood of Japanese origin made from fermented soybeans bringing various health benefits if rightly consumed.

The food smells like rotten beans that can harm you, but it is arguably on the opposite side. 

Yes, natto will rot if too many days have passed since it’s expired or if left in a hot and humid place for a long time.

Rotten natto, where natto bacteria isn’t dominant (various germs propagate), is watery and not sticky, or you may see mold on the surface.

Then, how about fresh natto?

Definition of Fresh Natto

Fresh Natto

I found the words when I googled natto in its Related Searches section, and I wondered, what is the definition of fresh natto?

So I looked up 新鮮な納豆 (meaning fresh natto) on Japanese google again and read through some articles.

Among them, I found this one very helpful. Based on the content,

fresh natto in the product form would be the one within the best-before date that is properly stored in the fridge at under 10 degrees Celsius.

Signs of Rotten

You can eat natto for a while even after it’s expired. But its taste and texture change over time, getting gradually worse.

10-14 days after it’s expired, natto will become blackish, not sticky, harden, and smell like ammonia.

Also, you may see white particles on the surface. But they are crystals of an amino acid called tyrosine, which is harmless.

Further going, if the beans become very watery or not stringy or mold grows on the surface, you should not eat them. Those are signs of rotten.


Hi, I'm Tomo, a Japanese blogger living in Niigata Prefecture, Japan. For the purpose of enriching your life, I would like to introduce things about Japan on this blog, especially unique Japanese products, cooking recipes, cultures, and facts and trivia.

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