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To finish the natto, you’ll need to warm the beans in the oven for several hours. Set the temperature to 200°F (93°C) and allow it to preheat fully. If your oven temperature doesn’t go as low as 200°F (93°C), use the lowest heat setting possible. You can even go as low as 100°F (38°C) if possible. Use a sterilized spoon to add a thin layer of beans to the bottom of 3 to 4 oven-safe glass jar. If any of the beans fall onto the counter or table during the transfer, discard them.  Make sure that the jars you use have lids. Sterilize the jars in boiling water before filling them. When the beans are in the jars, place a piece of sterilized cheesecloth over each one. Next, place the lids on the jars, closing them tightly. Once they’re closed, place the covered jars in the preheated oven. Allow the beans to ferment in the oven for 22 to 24 hours. You can also place the jars in a food dehydrator to ferment the beans. When the beans are finished fermenting, remove the jars from the oven. Let them cool for at least two hours. Once the beans are cooled, remove the lids from the jars and discard the cheesecloth. Replace the lids on the jars so they’re tightly closed once more. When the jars are recovered, place them in the refrigerator. Let them chill at least overnight or up to 3 to 4 days. Natto are often served as part of a Japanese breakfast. It can also be incorporated into your meals in other interesting ways.

Summary:
Preheat the oven. Add the beans to oven-safe jars. Cover the jars with cheesecloth and the lids. Place in the oven to ferment for 24 hours. Allow the natto to cool. Remove the cheesecloth and recover the jars with lids. Refrigerate the natto overnight.