There is a possibility that there is contamination from the natto bacillus at the fermentation process.
Natto bacillus is not only in the natto starter powder, but it can also be in our environments such as soil and the atmosphere where it is possible for natto bacillus to grow. We need to clean up the working environment and working tools, boil and sterilize them before begin making tempeh.
Please do not touch or eat natto in the middle of the tempeh making. You also need to wash your hands and make sure it’s clean during the tempeh making. These actions will prevent the contamination from the natto bacillus entering the tempeh.