All utensils and appliances that come into direct contact with natto must be soaked in boiling water at 100 degree in advance to kill miscellaneous bacteria. Isn't it disinfected when mixing and packaging? In addition, temperature control during fermentation is also very important. It is possible that although silk appears, the activity of Bacillus natto has decreased or died. But anyway, you can eat this, no problem.

Bacillus natto is an aerobic bacterium, so contact with air is very important. However, after fermentation, the lid should be covered and the mouth should be sealed with adhesive tape to avoid contact with air, which is conducive to long-term preservation.

The shelf life of natto is one week. During the period of low-temperature storage in refrigerator, natto is still undergoing slow low-temperature mature fermentation, and nattokinase and vitamin K2 are also increasing. However, although it can be eaten after the shelf life, it is just that Bacillus natto decomposes protein for survival, and the odor gradually increases. For natto stored for too long, it should be avoided.