Make natto at home
Making home-made natto is very easy to make as long as you have the right equipments and apply the correct hygiene. Ingredients for natto are only dried soybeans, water and natto starter (powder that contains millions of Bacillus natto spores). Traditionally small soybeans are used but you can make natto with any kind of soybeans, including black soybeans.
Soaking the soybeans
Clean and rinse the soybeans and soak them during 12 hours (summer) or up to 24 hours (winter) in sufficient water so they will double in size. It is important that the soaking water does not ferment by lactic acid bacteria, because the Bacillus natto will not grow on acidified beans.
Steaming the soybeans
Steam the soybeans until they are soft enough to easily crush between thumb and index finger.
This can be achieved by steaming them under pressure for 50 minutes. In a large pressure cooker put about 400 ml water, place the soaked soybeans in a basket and cook for 50 minutes at maximim pressure. Turn off the heat and let it slowly cool down for 15 minutes before opening the lid.
Inoculating the soybeans
Make sure that all containers and spoons to be used for fermenting are first sterilized in boiling water. Add the drained and hot soybeans in the fermentation container. Add about 1 g of good quality natto starter
while the beans are still steaming hot and mix the starter in the soybeans thoroughly. Put one layer of about 5 cm (2 inches) in a glass baking pan. Allow the beans to cool to below 45°C. Cover with plastic wrap to maintain humidity. Incubate between 8 and 20 hours at 40°C until the desired flavour and stringiness has developed.
Transfer the natto in another container that can be closed and keep for 1 or 2 days in the refrigerator. The natto will further ripen and develop more taste and stringiness. Enjoy your natto!