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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.

Storing natto

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!

Comments

Best natto starter?

What is better for using as a starter: natto spores or fresh natto (previous batch or store bought)?
Sigurd - 13/03/2015

Best natto starter

I always use powdered natto starter. It is so cheap as you need only a little bit of it. Using fresh natto makes it difficult to follow the process (the soybeans already smell like natto from the start) and the results may vary. You don't know what happened to store bought natto, maybe it has been frozen and defrosted a few times.
Lisa - 27/03/2015

Made own natto

Thanks for the instructions! I am very happy with the natto starter from nattostarter.com. Natto is super food, but also super easy to make.
Yasin - 23/02/2016

Natto without Neba-Neba

I am from Argentina (South America). Since early August 2015, I am attempting to make natto in small-scale for my family consumption.
Althought I tried different types of soybeans and three different types of Bacillus subtillis, I fail to produce natto with a substantial degree of stringiness. I am already aware that extreme cleanliness, oxygen, humidity and temperature are indeed relevant issues and I think I am taking care of these variables.
However, after purchasing some natto at a Japanese grocery store, I have the impression there may be some hidden raw materials that contribute to develop neba-neba such as molasses, organic sugar, inactivated brewers yeast and/or malt extract.
Could you please share with me you insights in order to correct my mistakes?
Martin - 17/04/2016

Natto without Neba-Neba

I don't think that there are secret ingredients. The Japanese use very small soybeans for making natto. Small beans have a lot more surface that large beans. For example, 5 mm soybeans have 60% more surface than 8 mm soybeans. Therefore there is more growth of Bacillus on small beans. But they are very difficult to find. I haven't seen them here in Europe. You should also make sure that the beans do not acidify during soaking process, for example by soaking 24 hours in cool place (fridge).
Rob - 17/04/2016

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