For many people outside Japan, the first encounter with natto is a moment of surprise. The small, brown soybeans are coated in a sticky, stringy web that stretches when you lift a bean with chopsticks. The aroma is a sharp mix of aged cheese, soy sauce, and a faint hint of ammonia. It’s a food that divides opinion instantly—some love it, others find it a challenge. But behind that unusual exterior lies a centuries-old fermented staple with a unique nutritional profile that has earned it a dedicated following.
Natto is made by fermenting soybeans with Bacillus subtilis, a bacteria that produces the enzyme nattokinase and creates the characteristic slime. The result is a food packed with probiotics, vitamin K2, fiber, zinc, manganese, and isoflavones. Whether you’re looking to explore a new cuisine or add a fermented food to your meals, understanding how to use and make natto can open up surprising possibilities. This guide covers what you need to know, from the basics to homemade batches and everyday serving ideas.
What Is Natto?
Natto is a traditional Japanese food made from soybeans fermented with Bacillus subtilis, a bacteria strain that transforms the beans into a sticky, stringy mass. The Complete Guide to Natto describes it as a staple in Japanese breakfasts, often served simply over rice. The fermentation process gives it a shiny, viscous coating and a texture that clings to everything it touches, which can be a shock for the uninitiated. Give Me Umami notes that the aroma is undeniably pungent—a blend of aged cheese, soy sauce, and ammonia—and the flavor is earthy and nutty with a hint of bitterness.
Despite its polarizing character, natto’s source-reported health benefits are substantial. The fermentation produces nattokinase, an enzyme associated with cardiovascular support, and the beans are rich in probiotics that may aid digestion. Both sources also highlight natto’s high vitamin K2 content, which plays a role in bone health, as well as fiber, zinc, manganese, and isoflavones. It’s an acquired taste, but for those who stick with it, the payoff is a nutritional powerhouse that’s been part of Japanese cuisine for centuries.
Before You Try: Managing Natto's Flavor and Texture
If you’re opening a pack of natto for the first time, the appearance and smell might make you hesitate. The surface is glossy and webbed, and the odor can fill a room. But there are simple ways to tone down the intensity. The most common advice from Give Me Umami is to stir the natto vigorously before eating. That 10–15 seconds of whisking with chopsticks thickens the slime and somehow mellows the pungency, making the flavor more balanced. Many people also add the little packets of soy sauce and mustard that come with store-bought natto; the sharpness of the mustard and the saltiness of the soy sauce cut through the earthy notes.
Storage matters too. Unopened natto keeps in the refrigerator for 7–10 days, according to Chopstick Chronicles. Freezing extends that to several months, though the texture can become slightly grainy after thawing—a small trade-off for convenience. Always check for signs of spoilage: an off odor beyond the usual funk, discoloration, or visible mold means it’s time to toss it. For first-timers, starting with a small amount mixed into a familiar dish (like a bowl of rice or a wrap) can make the experience less intimidating.
How to Make Natto at Home
Making natto from scratch sounds like a science experiment, and in a way, it is. You’re cultivating a specific bacteria on soybeans, and that requires a steady, warm environment. The process isn’t complicated, but it does demand attention to temperature. Here’s how to do it, based on steps from Chopstick Chronicles and Give Me Umami.
Step 1: Prepare the Soybeans
Soak dried soybeans in plenty of water overnight—at least 12 hours, so they double in size. Then cook them until they’re tender but not mushy. A pressure cooker does this fastest, but boiling them in a pot works too. Once cooked, drain the beans and let them cool to a temperature that won’t kill the bacteria. You’re aiming for warm to the touch, around 100°F (38°C). If the beans are too hot, the starter won’t survive; too cold, and fermentation stalls.
Step 2: Inoculate with Natto Starter
Now you introduce the bacteria. You can use a commercial natto starter powder, or a small spoonful of a previous batch of store-bought natto (the kind that’s still alive, not pasteurized). Sprinkle the powder or mix in the starter evenly, stirring gently so every bean gets coated. The bacteria need to be distributed well, but don’t be aggressive—the beans are fragile at this stage.
Step 3: Ferment at a Controlled Temperature
Transfer the inoculated beans to a shallow container. Cover with a breathable cloth or poke a few air holes in the lid—Bacillus subtilis needs oxygen. The key is maintaining a steady 100-110°F (38-43°C) for 20-24 hours. Some sources suggest extending that to 48 hours for a stronger flavor and more pronounced slime. A yogurt maker, an oven with only the light on, or a dedicated fermenter works well. After 20 hours, you’ll notice a white film and a slight ammonia smell; that’s normal. The longer it ferments, the stronger the aroma and the darker the beans become.
Step 4: Cool and Store
Once fermentation is done, refrigerate the natto for at least a few hours before eating. This chilling step helps set the texture and deepens the flavor. Store it in the fridge for up to 7-10 days, or freeze portions for several months. Fresh homemade natto has a livelier, more complex taste than many commercial packs, but it’s also more variable—each batch is a small adventure.
How to Eat Natto: Serving Ideas
If a spoonful of plain natto is too much of a leap, these serving ideas start with the most traditional way and branch into modern twists that can make the texture and flavor a little friendlier. Each suggestion is meant to help you find a comfortable entry point.
Classic Natto over Rice
This is the baseline: natto gohan. Stir the natto vigorously with the included sauce and mustard for 10–15 seconds until it’s thick and frothy. Pile it onto a bowl of hot steamed rice. The heat from the rice warms the natto slightly, softening the odor. Top with chopped scallions or (if you’re feeling adventurous) a raw egg, which adds richness. It’s a breakfast that’s both quick and deeply savory.
Natto with Miso Soup
For a gentler introduction, add natto directly to miso soup just before serving. The broth’s warmth tames the sliminess and dilutes the strong aroma, blending the natto’s earthiness with the miso’s umami. It’s a comforting bowl that doesn’t emphasize the texture as much as the plain beans do.
Natto with Grated Nagaimo
Nagaimo is a Japanese mountain yam with a crunchy, slightly mucilaginous texture. When grated and mixed with natto, it creates a creamy, crunchy combination that’s mild and surprisingly refreshing. The nagaimo’s clean flavor balances the natto’s intensity, and the dual textures—slimy and crisp—can be more appealing than the sticky beans alone.
Natto in a Wrap or Sandwich
For a thoroughly modern take, spread natto on a tortilla or bread with avocado, lettuce, and a drizzle of soy sauce. The creamy avocado and crisp lettuce cut through the slime, and the wrap format hides the visual aspect. It’s a quick lunch that uses natto as a savory protein spread, and even those who are hesitant often find this pairing approachable.
Common Mistakes and Troubleshooting
Even with good instructions, a few things can go wrong. Here are the most frequent pitfalls and how to avoid them.
One of the simplest oversights: not stirring enough. The sources say 10–15 seconds of vigorous mixing develops the texture and tempers the flavor. If you skip this, the natto tastes flat and the slime feels thin. Stir until you see the characteristic webbing form.
When making natto at home, temperature control is everything. If the fermentation temperature drops below 100°F, the bacteria may not grow enough; if it spikes above 110°F, they can die. Use a thermometer and check every few hours. A stable environment like a yogurt maker set to 104°F (40°C) works reliably.
Using too much natto starter is another common mistake. A little goes a long way—follow the package instructions, because an excess can lead to off-flavors or a slimy coat that’s too thick. If you’re using store-bought natto as a starter, a teaspoon-sized amount for a batch of beans is plenty.
Finally, always check for spoilage. Homemade natto should smell slightly ammonia-like but not rotten. Visible mold, a pinkish tint, or a truly foul odor means the batch is unsafe. When in doubt, discard it. The 7–10 day fridge rule is a guideline, not a guarantee—your nose is the final judge.