E
F
GH
Fig. E: You can home-ferment in an oven with a worklight for heat. Fig. F: If your oven is too warm, you can make a fermenter from a cardboard box lined in foil; a lightbulb is suspended from the lid.
Fig. G: Every 6 hours, remove the foil and inspect your beans. Finished beans will look dried and wrinkled. Fig. H: You should see telltale white, sticky strings when you lift a spoonful up from the mixture.
Pour the beans into the baking dish. Mix in 2– 3 Tbsp of commercial natto, and spread the beans evenly across the dish (Figure D). Carefully cover with a sheet of foil, and punch air holes in the surface. Some recipes suggest adding sugar or salt, or a bit of the bean water if the mixture seems dry. Mine turned out fine without any of these additions.
The natto bacteria must now grow at about 104°F. If you have a modern oven, place the baking dish on its top shelf, next to your thermometer. Put the work light on the oven floor, turn it on, and close the door (Figure E). Every hour, check the temperature. You may have to change the wattage of your bulb or prop the door open to get it right. Don’t worry if the temperature fluctuates; I’ve hit as high as 122° and as low as 95° before leveling out at 104°.
If, like me, your oven runs too hot or you can’t trust your roommates to leave it alone, use a cardboard box or a cooler instead (Figure F). Or adopt the style of Yoko Kondo, who ferments and pickles food for Minako Organic, her Japanese restaurant in San Francisco. Ever since she was a student in
Japan, Kondo has wrapped her foil-covered baking dish in 3 bath towels and left it out to ferment for a full day in direct sunlight. In the winter, she puts the package in her bed under the covers.
Every 6 hours, remove the foil and inspect your beans (Figure G). Finished beans will have dried, darkened, and wrinkled on the surface, and should give off a light aroma of ammonia. Pull up a spoonful with a sterilized spoon, and you should see the telltale white, sticky strings (Figure H). If you haven’t achieved these results after about 24 hours, something likely went wrong. Cover and store successful natto in the refrigerator for 1– 2 days to let its flavor develop. It will last for 2 weeks in the fridge, and the bacteria can survive frozen for 2 months.
Natto is traditionally served at breakfast, mixed with rice, spicy mustard, soy sauce, and chopped green onions.
When he isn’t playing with rotting food, Eric Smillie writes for magazines.
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