"Natto does not ask to be liked. It asks to be understood.
"KaiRenner26th of April 2026
What Natto Is and Why It Ferments Differently
Natto is made by fermenting cooked soybeans with Bacillus subtilis var. natto, a bacterium that thrives at temperatures around 100 to 110°F. Unlike most ferments, natto does not use salt, acid, or anaerobic conditions. It needs warmth, humidity, and oxygen. The bacteria produce nattokinase, a notable enzyme, along with the characteristic sticky strings and pungent ammonia-forward aroma that define the ingredient.
100to 110 F
22to 24 Hours
Soak and Cook the Soybeans
Soak soybeans overnight, then pressure cook or boil until very soft.
Soak and Cook the Soybeans
Soak 500g of dried soybeans in three times their volume of water for 12 to 18 hours. Drain and rinse. Pressure cook at high pressure for 20 minutes, or boil for 3 to 4 hours, until a bean crushes easily between two fingers with zero resistance. Drain and keep hot — you will add starter while beans are still steaming. Do not let them cool before inoculation.
Inoculate with Natto Starter
Dissolve starter spores in water and mix into the hot drained beans.
Inoculate with Natto Starter
Dissolve one packet of natto starter spores in 2 tablespoons of warm sterile water. Pour over the hot drained beans and mix thoroughly with a sterilized spoon. Work quickly — you want beans hot and starter evenly distributed. Spread into shallow sterilized trays to no more than 1 inch deep. Surface area and airflow matter more than depth.
Ferment in a Warm Environment
Hold at 100 to 110 F for 22 to 24 hours with some airflow.
Ferment in a Warm Environment
Cover trays loosely with foil or a breathable cloth — not airtight. Place in your oven with just the light on, a dehydrator set to 105°F, or a purpose-built fermentation chamber. Check temperature every few hours. At around 18 hours a white film and visible strings will appear. At 22 to 24 hours the beans are done. Refrigerate immediately to stop fermentation.
Rest Before Eating
Refrigerate for 24 hours to mellow flavor before eating.
Rest Before Eating
Fresh natto has a sharp ammonia edge. Refrigerating for 24 hours allows flavor to mellow and the strings to firm up slightly. Properly made natto will pull long strings when stirred with chopsticks. Season with soy sauce, mustard, and sliced green onion. Keeps refrigerated for up to a week.
What You Need
500g dried soybeans
Natto starter spores (available online)
Pressure cooker or large stockpot
Shallow sterilized trays or containers with holes for airflow
Thermometer — holding 105°F is critical
Oven with light on, dehydrator, or fermentation box
Temperature Control Is Everything Below 95°F, Bacillus subtilis grows too slowly and other bacteria compete. Above 115°F, the culture dies. A probe thermometer inside your fermentation chamber is not optional — checking once is not enough. If your oven light runs too hot, prop the door open slightly or use a lamp box instead.
"The strings are the sign. Pull them with chopsticks and you will know it worked.
"KaiRenner26th of April 2026