Vegans and Vegetarians (and omnivores!) rejoice! Here is a simple way to make your own natto!
It does require a little sneaky trick for the first batch (like for yoghurt) but from the second batch it will all yours and only yours!
As usual, as this is a basic recipe, I willl explain step by step, and mentioning the quantities on the way!

Firts the soy beans (daizu/大豆 in Japanese).
Use a large vessel as you will need 2 to 3 times as much water: 1 volume of soy beans + 2~3 volumes of water.
Make an effort touse clean cold water!
Let the the soy beans soak overnight.

You will discover that after a night of soaking the soy beans will have changes in shape from round to elongated!

Next you must steam the soy beans (preferably the slow way) for three hours to get them soft, otherwise they will not ferment. You may use a pressure cooker, but you will have to expperiment!

Important point: From now on, especially, make sure that all vessels and utensils you use are properly boiled in hot water first to kill all germs, or you will end with a yeast/germ/mold battlefield!
Use a large metal shallow vessel for even wieght and spread.
Transfer the steamed soybeans on eat as shown in above picture.
Be aware that the smell will be strong, so choose your room!

Now, for the all-important “sneaky” trick!
The beauty of it is that from the second batch you will use your own batto! Friends with some knowledge in yoghurt or Japanese sake fermentation will easily understand!
Drop a few grains of natto bought at the market in half a cup of water/ 100~cc/ml. (use high quality non-gaseous mineral water!)
After stirring 2 or 3 times, the water should start turning whitish. This is your yeast/fermentation starter!

Carefully pour the fermentation starter (with the natto beans) evenly all over the steamed soy beans.

Cover/wrap the whole with cellophane paper. Punch small holes (about 20) with a toothpick to allow ventilation.

Tap the cellophane paper so as to keep it close in contact with the soybeans. Do not press.

Now, the whole important thing: the temperature!
Like for Japanese Rice fermentation, it must stay between 30 and 40 degrees Celsius. There are many ways to do it if you do not have the right room for it: use a hot water bottle (above) put nearby and cover it with a blanket, or put it under a heated blanket….

keep checking the temperature!

Let ferment for 20 hours.
Upon lifting the cellophane paper, the natto should show white filaments.

Here is the finished product!
True to tell, home-made natto might not as “sticky” as natto bought in markets, but this is still true natto.
Actually, the lack of “stickiness” might be be a blessing for some!

Keep in mind this is a true food, especially for vegans and vegetarians who are in more need of nutrients than omnivores!

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