Natto

What is natto?

Benefits of natto

How to buy or source natto starter

Natto recipe

References

What is natto?

Natto is a traditional Japanese fermented soybean food made by inoculating cooked soybeans with the beneficial bacterium Bacillus subtilis var. natto. It has a unique sticky, slimy texture with long viscous threads (a bacterial biofilm), a pungent earthy ammoniacal aroma, and a strong savoury, nutty flavour. (1)

You can make natto using other legumes, such as chickpeas or black beans. My favourite natto is made with black beans, and that is mostly what I use today. Black beans have a deeper more intense flavour, arguably a better health profile, and have less or no stringiness.

Natto is one of the oldest fermented soy foods in Japan, with origins possibly dating back over 1,000 years. According to legend, it was discovered when soybeans were wrapped in rice straw (which naturally contains the bacteria) and left to ferment. It is a living probiotic food particularly valued for producing nattokinase (a powerful enzyme) and vitamin K2 (MK-7) during fermentation. (2)

Fermentation improves the digestibility of soybeans, reduces antinutrients, and creates bioactive compounds not present in unfermented soy.

Benefits of natto

Natto is nutrient-dense and offers several science-backed health benefits:

• Cardiovascular health - Nattokinase has strong fibrinolytic (clot-dissolving) activity, helps improve blood flow, lowers blood pressure, and may reduce arterial plaque. Regular natto consumption is associated with lower risk of cardiovascular disease. (3, 4)
• Bone health - One of the best dietary sources of vitamin K2 (MK-7), which helps direct calcium into bones and teeth while preventing calcification in arteries and soft tissues. Linked to improved bone density and reduced fracture risk. (5)
• Gut and immune support - Bacillus subtilis acts as a robust probiotic that survives stomach acid, supports a healthy microbiome, aids digestion, and may enhance immune function. (6, 7, 8)
• Anti-inflammatory and antioxidant effects - Contains isoflavones, polyphenols, and other compounds that combat oxidative stress.
• Other benefits - May support healthy blood sugar levels and contribute to the longevity observed in traditional Japanese diets high in natto. (7)

A typical serving provides high-quality plant protein, fibre, and essential nutrients while remaining relatively low in calories.

How to buy or source natto starter

Purchase ready-made natto from Asian grocery stores (refrigerated section).

Buy pure Bacillus subtilis natto spore powder online (a tiny amount is sufficient for many batches).

Use 1-2 tablespoons of good-quality fresh natto as a starter for homemade batches.

Natto recipe

Ingredients (makes 10 servings)

2 cups (300-400 grams) dried organic soybeans (preferably smaller-sized beans). Alternatively use black beans.

Natto starter: 1/8-1/4 teaspoon natto spore powder, OR a tube of purchased starter powder OR 2 full tablespoons of fresh natto.

Filtered water for soaking and cooking.

Equipment

Large pot with a steaming tray or a pressure cooker.

Cheesecloth, breathable cover, or plastic wrap with holes.

Incubator (yogurt maker, oven with light on, or warm spot maintaining 37-42C / 98-108F). I use a Luvele yogurt maker.

Method

Soak the beans in plenty of water for 8-12 hours. They will double in size so allow sufficient space. Rinse the beans at least twice in clean water and drain.

Cook until soft but not mushy. Pressure cooker: 20-30 minutes. Stovetop in steaming basket: 7 hours. Simmer in water just covering the beans: 3-4 hours.

Steaming gives the best results. Save the water remaining after steaming to cool and use a little with the starter.

Drain thoroughly and cool to about 40-50C (still warm but not uncomfortably hot to the touch). There should be no liquid remaining.

Inoculate. Mix the starter powder with 1-2 tablespoons of 40-50C water. If using a previous fresh natto as starter, mash them and mix into a slurry with warm water. Mix the warm beans evenly with the starter in the brewing bowl, container or tray. They must be clean or preferably sterilised.

Cover the container loosely to allow some air exchange. Maintain at 37-42C for 18-24 hours until thick sticky threads form and it develops a characteristic aroma. A thin white coating is normal.

Mature. Stir to aerate. Refrigerate for at least 24 hours (flavor improves and is at its best after a few days or a week). Keeps 1-2 months in the fridge.

Serving suggestion: Serve over steamed rice with a little soy sauce, mustard, chopped green onions, and optionally a raw egg yolk. Mix well to enjoy the signature strings.

Tips for Success & Troubleshooting

Consistent warm temperature is critical during fermentation.

Bacillus subtilis is hardy, but maintain good basic kitchen hygiene.

No/little stickiness: temperature issues or weak starter.

Bad (rotten) smell instead of strong fermented aroma: discard and try again. Ammonia, a strong, pungent gas can occur when brewing natto, and this is acceptable.

Your comments about any of your experiences - positive or negative - with your use of natto are welcome at Grow Youthful. I am always curious about your use of and experience with natural remedies, and your feedback is very welcome.

References

1. Afzaal M, et al. Nutritional Health Perspective of Natto: A Critical Review. PMC. 2022. PMC9616652/

2. Kaneki M, et al. Japanese fermented soybean food as the major determinant of the large geographic difference in circulating levels of vitamin K2. Nutrition. 2001.

3. Chen H, et al. Nattokinase: A Promising Alternative in Prevention and Treatment of Cardiovascular Diseases. Biomarker Insights. 2018.

4. Li X, et al. Nattokinase Supplementation and Cardiovascular Risk Factors. PMC. 2023.

5. Wen Z, et al. Habitual natto intake elevates serum MK-7 levels, enhances osteocalcin carboxylation, and supports bone density: a meta-analysis of Japanese evidence. Frontiers in Nutrition. 2025.

6. Tsukamoto Y, et al. Intake of fermented soybean (natto) increases circulating vitamin K2 (menaquinone-7) and gamma-carboxylated osteocalcin concentration in normal individuals. J Bone Miner Metab. 2000.

7. ono K, et al. K Fluctuations in Intestinal Microbiota Following Ingestion of Natto. PMC. 2022.

8. Lenini C, et al. Probiotic properties of Bacillus subtilis DG101 isolated from natto. Frontiers in Microbiology. 2023.