How to Enhance the Fermentation of Natto

Written by steve sparkes
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How to Enhance the Fermentation of Natto
Natto is often added to miso soup as a condiment. (clear soup with noodles image by Maria Brzostowska from

Natto is a traditional Japanese food made by fermenting soya beans. It is nutritious and is used as a medicine as well as food in Japan. Its health properties derive partly from its vitamin K, fibre, antioxidant, lecithin, calcium and protein content. However, its more unusual health benefit is due to the nattokinase found in this particular dish. Nattokinase is an enzyme that works well as an anticoagulant. It is also inexpensive, and along with its other health benefits, makes a great, non-pharmaceutical alternative to other anticoagulants. It is a bit of an acquired taste but worth sticking with if you can learn to enjoy it, for these reasons.

Skill level:

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Things you need

  • 500 grams of small, organic, non-genetically modified soybeans
  • Natto-kin
  • Steamer or pressure cooker
  • Water
  • 1/2 tsp salt
  • 1/2 tsp brown sugar
  • Warm environment (over 4.44 degrees Celsius)

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  1. 1

    Buy small and preferably organic and not genetically modified soybeans. The smaller the soybeans are, the easier the enzymes will reach the middle during fermentation.

  2. 2

    After rinsing the soybeans, soak them until they are about 3 times the size they were when dry. This allows more surface area for the fermentation process to work. Because you bought small beans in the first place, the beans will be less dense and easier for the enzymes to get through.

  3. 3

    Use Natto-kin, or natto bacillus spores, to initiate the fermentation process. Add it to the beans after you have steamed them until they are soft (for approximately 6 hours or just 45 minutes using a pressure cooker). Add the Natto-kin to the beans whilse they are still steaming hot. "Natto-kin can live in extreme circumstances and ... the 'heat shock' should boost the bacteria activity and ensure better fermentation results," according to the Natto King website.

  4. 4

    At this stage, as well as adding a little salt for flavour, add some sugar too as an aid to fermentation. Approximately half a teaspoon of brown sugar per 500 grams of beans is ideal. If you overdo the sugar the resulting Natto may be too sweet.

  5. 5

    Ferment the beans in a warm environment for at least 24 hours, preferably at a temperature greater than 40 degrees Celsius for optimum fermentation.

Tips and warnings

  • Keep utensils and beans clean. A sterile environment will prevent potentially unwanted bacteria forming during fermentation.
  • After fermentation, keep the Natto in the refrigerator for up to a week to age the Natto. This will make them taste better and give them a better, stringier, texture.
  • If you are prescribed anticoagulants by your doctor, do not stop taking them. Follow your doctor's advice. However, Natto can be eaten by healthy people as a preventive measure.

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