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1
Wash the soy beans well, and soak in plenty of water for 15 hours.
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2
Pour at least 600 ml of water to the steaming rack, and insert the steaming basket.
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3
Wrap the soy beans in a bleached cotton cloth/cheesecloth, and place in the steaming basket.
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4
Steam in the pressure-cooker (30-40 minutes over medium heat after the cooker reaches pressure).
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5
In the meantime, sterilize the following equipment in boiling water: containers with sieve inserts the lid of a pot spoon.
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6
Allow the pressure cooker to de-pressurize naturally (natural release method), and using a tongs remove the wrapped soy beans.
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7
Place in the sterilized lid.
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8
Leave 25-50 ml of the steaming liquid in the bottom of the pressure cooker pot.
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9
Add about 0.3 g (3 spoonfuls of the tiny spoon that comes with the natto kin; it's best to be generous) of the natto kin and mix to dissolve.
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10
Add the Step 4 steamed soy beans back to the pressure cooker pot.
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11
Shake the pan around to thoroughly mix the beans with the natto kin.
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12
Using the Step 3 sterilized spoon, fill the sterilized sieve inserts of the steralized containers with the beans to about 2 cm below their rims.
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13
Cover each container with a paper towel, and then seal with the lids or plastic wrap.
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14
Don't seal so that they are airtight and leave a little gap.
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15
Ferment the beans in an oven at 38-42C.
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16
Set the temperature using the oven light, a fluorescent bulb, or a bowl filled with hot water.
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17
If you put the beans too close to the bulb, they'll dry out so, so be careful.
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18
Make sure the paper towels don't touch the beans.
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19
Change the paper towels halfway through the fermentation process.
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20
24 hours later, if the surfaces of the soy beans are completely covered with white spores and are sticky, the natto is done.
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21
Wipe off any condensation from the lids, cool the beans down and store in the freezer.
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22
To defrost, microwave for 20 seconds.
