1. Natto has the odor of ammonia. The ammonia odor is produced when Natto bacteria decompose protein. Many people who eat natto believe that the ammonia odor of natto is special. People who hold this view of "umami" taste and "fragrant" taste do not want to change the taste of natto.

A natto machine is a device used to ferment natto. Since Natto bacterium is a special aerobic bacterium and its growth temperature is higher than that of ordinary bacteria, there are three special requirements for the machine that ferments natto.

First, ventilation and oxygen supplementation. Natto machines are different from yogurt machines. They must have the function of ventilation and oxygen supplementation. Without sufficient oxygen, the natto bacteria cannot grow normally. The natto produced by fermentation in devices without ventilation and oxygen supplementation functions will have low contents of various effective substances. Not even much different from ordinary soybeans.

Second, constant temperature. The growth temperature of Natto bacteria is between 38℃-45℃, and the optimal growth temperature is between 40℃-42℃. The whole process of natto fermentation should be maintained at a constant temperature. Natto bacteria cannot grow beyond the temperature range. Third, humidity. During the growth process of Natto bacteria, it not only requires oxygen and temperature, but also requires maintaining a certain humidity. There should be sufficient moisture in the environment so that Natto bacteria can thrive.