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For the natto, you’ll need 4 cups (800 g) of soybeans. Place the beans in a colander or strainer, and rinse them thoroughly under cold water in the sink. Shake the beans well afterward to remove the excess moisture. As you rinse the soybeans, remove any shrunken or discolored beans. After you’ve rinsed the soybeans, place them in a large pot. Cover the beans with 12 cups (2.8 l) of cold water to create a ratio of 3 parts water to 1 part beans so the beans have room to expand. Allow the beans to soak for 9 to 12 hours. During colder months, you may need to soak the beans longer, so it may take as many as 15 to 20 hours. When the beans have finished soaking, dump them into a colander or strainer. Shake well to remove all of the excess moisture.
Wash the soybeans. Soak the beans overnight. Drain the beans.