How To Make Natto

There are a number of different ways to make natto. This recipe is by Kazuo Shiroki, and it uses natto bacteria (bacillus natto). Bacillus spores are more economical and reduce the risk of contamination. If you use commercially produced natto in place of the natto bacteria, then substitute one pack of natto for 0.0035 ounces or 0.1 gram of natto bacteria in this recipe. You can obtain bacillus natto spores from a small company called Gem Cultures. You can contact them at 707-964-2922 ask for the 4.5 lb natto starter kit.
If you just want the clot buster enzyme capsules containing nattokinase (Nattozyme) it is available through NutriCology 800-545-9960.


A bowl to immerse (completely cover) the soybeans
A sieve to drain the soybeans
A steamer
2 casserole pans, about 10” x 2” deep
Aluminum foil
2 pie plates to hold water, about 8” to 12” round
An oven thermometer
Rubber gloves (disinfect in hot water before using, to prevent contamination.)
1 heat resistant cup, teaspoon, and spatula
1 work lamp without a shade (optional)
1 40 watt bulb (optional)

Ingredients: (makes 2.6 lbs. of natto)

17.5 oz soybeans (smaller soybeans are better)
0.1 grams of Bacillus natto bacteria or (substitute 1 pk. of commercial natto)
¼ tsp. natural salt
½ half tsp. brown sugar or molasses


1. Wash the soybeans thoroughly, and soak in three times the amount of water (by volume) for 12 hours at room temperature.

2. When soybeans have swollen to twice their dry size, steam them in the steamer for six hours or until they can be easily mashed between two of your fingers.

3. Two hours before soybeans are finished steaming, make air holes in the aluminum foil. (Without enough air circulation, natto may become bitter; with too much, its surface may become dry.) Cover empty casseroles pans with aluminum foil and place on top oven rack.

4. Fill deep plates halfway with water and place on middle oven rack. (The water will keep the natto from drying out.) Also put heat resistant cup and teaspoon in the oven. Heat oven to 250 degrees to sterilize the utensils (this reduces the chance of contamination) and warms the water at the same time. When the oven has been adequately heated, turn it off and allow it to cool naturally.

NOTE: It is essential to maintain a temperature of approximately 104 degrees for successful fermentation.
Work quickly from this point on, in order to prevent introduction of harmful bacteria.

5. When finished steaming soybeans, strain water by keeping lid in place while tipping the steamer. (Be careful not to burn yourself with the hot water.)

6. Remove lid and steamer, leaving soybeans in the pot. Put lid back on quickly so as not to contaminate the soybeans and lose heat.

7. Pour 2 teaspoons of pre-boiled water into cup. Mix in salt, sugar, and one gram of natto bacteria. (Natto bacteria spores are very resistant to heat. It will take one hour at approximately 285 degrees to kill the natto bacteria.) Make sure that your pre-boiled water is below 175 degrees before adding natto bacteria spores.

8. Remove lid form pot, sprinkle salt, sugar, and natto bacteria solution over soybeans, and then stir to evenly distribute the natto bacteria.

9. Carefully uncover casserole pans and spread soybeans in a one inch thick layer. (Soybeans should be no more than 3 beans deep.) Re-cover the casserole pans with the aluminum foil.

10. Make sure the oven has cooled, then place the covered pans on the top rack. Leave the plates filled with water on the middle rack. The water should have cooled to around 105 degrees.

11. Place the work lamp fitted with the 40 watt bulb in the lower part of the oven. (You may use the oven light, but it will not warm the oven evenly.)

12. Place thermometer on the upper rack and close the door. Check the temperature after a few hours. To keep oven temperature between 100 degrees and 107 degrees, you may have to change the light bulb to a different wattage or keep the oven door propped open a crack.

13. Natto will be ready in 20 to 24 hours. After that, switch lamp off and wait a few hours until it cools, stopping the fermentation. when the aluminum foil is removed, soybeans may have turned partially white, and you will be able to smell the natto. Some ammonia smell is normal, but if it is too strong, undesirable germs may have flourished.

NOTE: Natto is very sensitive to air circulation, temperature, etc., so this can affect the outcome of the fermentation. If the fermentation is not successful, the finished natto may not be sticky or stringy, it may be bitter, or may have a strong ammonia smell.

14. Age natto in the refrigerator for up to one week. It will develop a nice stringiness and improved taste. If left in the refrigerator too long, however, the amino acids will crystallize and the texture will be sandy. The best way to prevent this is, after aging it, to divide it into several small packages and freeze them.

Natto is said to aid and even prevent several diseases and illness, some claims are backed by research and others are not. It is said that natto aids in the prevention of heart attacks, strokes and senility. Natto also aids in the prevention of osteoporosis, cancer, obesity, and intestinal disorders. It improves digestion not only in humans but also in our pets, such as cats and dogs. Natto has also been proven to be an anti-bacterial agent according to Japanese research.
Natto can be difficult to eat because of the smell and texture; here are some ideas that may help with this.

1. Natto Mabo-Tofu: Natto can be combined with mabo-tofu which gives it a natural almost nutty flavor.

2. You can add a few drops of vinegar; this will help with the strong smell of natto.

3. Cold natto does not have much smell, so you may want to avoid heating it. You can mix natto with yogurt and crushed grains of all kinds. You can also add fresh or dried fruits and nuts. By mixing with yogurt the slimy texture dissipates. Mix about 250 grams of yogurt with one pack of natto and add more yogurt if needed.

4. Most people just add some soy sauce and serve over hot rice. You can also add chopped green onions and or finely chopped cheddar, mozzarella, or havarti cheese. Let the cheese melt over the hot rice before adding the natto.

5. You can stir in some mayonnaise and add a few drops of soy sauce to your natto, then spread on bread.

6. Some people have tried and like natto with either mustard or even tobasco.

Natto seems to be very versatile; you can try different things for different flavors. We really hope that you enjoy your natto and receive all the health benefits it has to offer you.