Rinse navy beans and place them in a large glass bowl. Cover with enough filtered water to allow the beans to roughly double in size as they expand. Leave on the counter for 8 hours or overnight.

Drain the soaking water and place beans in a large pot. Cover with fresh filtered water.

Bring the beans to a boil, turn down the temperature to a simmer, affix the lid and cook the beans for 45 minutes until soft but not mushy.

Drain the beans and place in a large VitaClay slow cooker or crockpot. The beans should be no more than 1" in depth. Discard any beans that may accidentally spill during the transfer from the pot to the cooker.

Let the beans cool for 10 minutes.

While the beans are cooling slightly in the Vitaclay or slow cooker, dissolve a packet of natto starter in 3 Tbsp of warm filtered water. Alternatively, use 1/4 cup of your previous white natto batch as the starter.

Place the lid on the VitaClay and select the "yogurt" setting.

If using a different type of slow cooker, use the setting that will keep the beans between 100-110 °F/ 38-43 °C which is the temperature range necessary to ferment the beans into natto.

After 24 hours, turn off the Vitaclay, remove the lid, and cool the natto to room temperature for 1 hour. A whitish film and an ammonia-like aroma means they are done. The beans will also have a stringy and slimy appearance (see photo above).

Place the cooled natto in a glass container with a tight-fitting lid and refrigerate.

Natto will be ready to eat once refrigerated overnight. It will last for months, and the flavor will age and strengthen with time.

Navy beans are low starch and legal on the GAPs diet. They are also soy-free, so 1-3 tablespoons per day is a safe and inexpensive soil-based probiotic source as well as an excellent Vitamin K2 food source.