Natto is a… gooey, slimy, interesting looking Japanese traditional fermented soy beans.
Some people mention the similarity of the taste with Tempeh, the Indonesian fermented soy beans.
It looks scary and smells… like Natto, but many Japanese love it.


Makes approximately 3 cups (750ml) of Natto


  • 1.5  cup/250g    dry soy beans
  • ¼ tsp   Natto starter (spore)

*1 cup = 250ml


1     large pot, slow cooker or pressure cooker to cook beans
1     large strainer
1     mixing spoon
1     measuring spoon
1     thermometer with sensor on a cable
9” x 9” x 2 ½” glass or plastic container
large cooler box
1     large 4~6” deep container with lid (to hold hot water)
1     tea towel
Paper towel
Blanket to cover cooler box


  1. Wash and soak soy beans in water for 16~24hrs (beans will become 3 times larger).
  2. Cook soy beans until it becomes soft enough to be crushed easily between your thumb and pinky finger – pot simmering for 6-7 hours, slow cooker shimmering for 10 hours or longer, pressure steaming for 30 to 40 minutes. Drain well.
  3. In the meantime line the container (9”x10” or alternative) with paper towel. Boil 1.5 to 2L hot water.
  4. Sprinkle Natto starter over drained beans and mix thoroughly. Spread hot beans over the lined container, not more than 3cm/1” thickness
  5. Set the thermometer. Cover lightly with paper towel and the lid or tea towel. Set in the cooler box with another container of hot water (see figure). Set the cooler lid loosely. Wrap the box with a blanket (optional)
  6. Maintain the temperature above 105F°/40C° for 14 hours or longer.
  7. When the flavor becomes as you like, cool and refrigerate for 3 days to a week to cure.



  • Soak beans in a plenty of water and long enough. Split a few beans and check the centers. They should be smooth and full, not wrinkled.
  • Cook beans soft enough. If you use a pressure cooker, steam rather than shimmer for safety.
  • Excess moisture deteriorates the end result. Drain beans well.
  • Natto fungi need oxygen. Do not make the containers and cooler box air tight.
  • Do not drop the temperature lower than 100F°/38C°. If temperature becomes below 105F°/40C°, replace the container of hot water with hotter ones, possibly almost boiling water.
  • Give some air space between hot water and Natto container, especially in case the water is very hot.
  • Refrigeration/curing increases the Natto’s flavor.
  • Keep the workspace, utensils, containers and your hands clean.
  • Koji culture : GEM Cultures, Inc. (US)
  • Sterilize the utensils and work space thoroughly. Do not consume it if anything is suspicious.

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