If you’re a fan of traditional Japanese food, you’ve probably heard of nattō—those sticky, fermented soybeans packed with probiotics and umami goodness. While nattō is a staple in Japan, finding fresh, high-quality nattō outside the country can be a challenge. But here’s the good news: you can make nattō at home, no matter where you live!
In this guide, I’ll walk you through the process of fermenting nattō from scratch, using simple ingredients and tools. Whether you’re a fermentation enthusiast or just curious about trying something new, making your own nattō is a rewarding experience. Plus, homemade nattō lets you control the flavor and texture, so you can customize it to your taste.
Let’s dive into the world of nattō fermentation and bring a taste of Japan to your kitchen!
What is Nattō and Why You Should Give it a Try
Nattō (納豆) is a traditional Japanese food made from fermented soybeans. Known for its sticky texture, strong aroma, and unique umami flavor, nattō has been a staple in Japanese cuisine for centuries. It’s commonly eaten for breakfast, served over hot rice with soy sauce, mustard, and spring onions. It can also be seen as a side dish in many homes and restaurants.
But nattō is more than just an acquired taste—it’s a nutritional powerhouse. Packed with probiotics, vitamin K2, and protein, nattō supports gut health, strengthens bones, and may even help with heart health. The fermentation process produces Nattokinase, an enzyme known for its potential blood-thinning and cardiovascular benefits.
Why I Started Making Nattō at Home
For me, making nattō at home was a decision born out of both necessity and health benefits.
My husband is Japanese, and we live in Finland. While we try to incorporate Japanese foods into our diet, it’s not always easy. Nattō is available in a few specialty stores, but it’s very expensive—too costly to eat regularly. That’s why we decided to start making it ourselves. By fermenting nattō at home, we can enjoy it every day without worrying about the price.
On a personal level, nattō has also played a role in my health journey. I was diagnosed with ulcerative colitis, and after years of extensive research and self-experimentation, I’ve found that diet and exercise are key to managing my symptoms. One of the biggest game-changers for me has been incorporating fermented foods into my daily routine.
Nattō is an easy, delicious, and affordable way to support gut health, and it has become a staple in my diet. In a future blog post, I’ll share more about my journey with ulcerative colitis and what has helped me heal—but for now, let’s focus on how you can make nattō yourself!
What to Keep in Mind
Making nattō at home is a rewarding process, but it does come with a few challenges. To ensure success, here are some important things to keep in mind before you start.
1. Read the Entire Guide Before You Begin
Unlike some other fermentation processes, nattō requires precise timing and quick execution in certain steps. If you pause to read the instructions while in the middle of a step, you might risk contamination or affect the fermentation process. Take the time to read the entire guide beforehand, so you know what to expect and can move efficiently when needed.
2. Nattō Takes Time – Plan Accordingly
From start to finish, making nattō takes about three days. Most of this time is passive, meaning you don’t have to actively do much, but you still need to check on it every few hours. This means you should schedule your nattō-making during a period when you won’t be traveling or too busy to monitor the fermentation. If you’re looking for a weekend project, starting on a Friday afternoon or Saturday morning might be ideal!
3. The Type of Soybeans Affects the Texture
One thing we learned from experience is that not all soybeans behave the same way. The first time we made nattō, we followed the instructions exactly, yet the beans ended up a little too firm. After some experimenting, we realized that the size of the soybeans affects the final texture. Larger beans require a longer steaming time, while smaller beans cook faster. If you prefer a softer texture, extend the steaming time; if you like firmer nattō, reduce it slightly. Don’t be afraid to experiment and adjust the process to your taste!
4. Be Prepared for the Smell
If you’ve ever had nattō before, you know it has a very distinct aroma. That smell doesn’t just disappear once the fermentation is done—it tends to linger on equipment and even in the surrounding area.
Here’s what we’ve learned:
- The towel, hot water bottles, and thermos case you use for fermentation will smell like nattō for a long time, even after washing.
- Our balcony permanently smells like nattō because we store our empty thermos case there after use! We don’t mind it, but if you’re sensitive to odors, keep this in mind.
- We now use a dedicated towel just for nattō-making because the smell is tough to remove completely.
- Adding a disinfecting fabric softener to the wash helped us get rid of some of the odor from cloth materials—feel free to try it if needed!
If you’re making nattō for the first time, be mindful of where you do it and what equipment you’re willing to sacrifice to the nattō smell!
Equipment and Ingredients
Before you start making nattō, it’s important to have everything prepared. Since some steps need to be done quickly, having all the ingredients and equipment ready will make the process much smoother.
Please Note:
The amounts listed below will make enough nattō to last two people for around two weeks, assuming you eat one portion each per day. If you want to make more or less, feel free to adjust the amounts accordingly. Just keep in mind that a larger batch requires a bigger thermos case for fermentation.
Ingredients
For the Nattō:
- Soybeans – 400 g
- Water (for soaking and steaming)
- Nattō starter – 50 g (either store-bought nattō or some from a previous homemade batch)
For the Sauce (Optional, but Recommended):
- Soy sauce
- Mirin
- Water
- Dashi (powdered or homemade)
The sauce ingredients don’t have strict measurements—you can adjust them to taste. A simple mixture of soy sauce, mirin, and dashi enhances the flavor of nattō, making it even more enjoyable.
Equipment
For Cooking the Soybeans:
- Steamer basket (for steaming the soaked soybeans)
- Kitchen cloth (used during cooking)
- Large kettle with a lid (for steaming the soybeans)
- Water boiler or kettle (for heating water)
- Measurement cups (1 dl and 1 tablespoon)
- Strainer (for draining the soaked soybeans)
For Fermentation:
- Thermos case (ours have the following measurements, measured from the inside: width 35cm, height 28cm and depth 27cm). For a smaller batch, a normal cooler bag works as well.)
- Hot water bottles (We use one large (2L) and one small (0.5L) bottle to maintain the temperature inside the thermos case.)
- Towel (for additional insulation inside the thermos case)
For Handling the Nattō:
- Ladle
- Spoon
- Cling film (to cover the fermentation containers) (for making small holes in the cling film)
- Toothpick (for making small holes in the cling film)
- Storage containers (We use five containers of different sizes, ranging from 0.5L to 1L each.)
- A small dish for mixing the nattō starter with water
For Preparing the Sauce:
- Small dish (for mixing the sauce ingredients)
Having everything measured, cleaned, and ready to go will make the nattō-making process much smoother. Once you have all your ingredients and tools set up, you’re ready to begin!
The Step-by-Step Guide
- Measure 400 grams of soybeans and rinse them thoroughly under running water.
- Place the rinsed soybeans into a large kettle.
- Add 1 liter of water to fully submerge the beans.
- Leave the kettle in a safe place at room temperature, uncovered. The soybeans will swell and absorb water, roughly doubling in size.
- Keep the soybeans like this for about 24 hours.
- Add some water into a large kettle and bring it to a boil.
- Keep the heat low—the water should be just enough to touch the bottom of the steamer basket.
- While you wait for the water to boil, you can prepare the steamer basket.
- Cover the steamer basket with a kitchen cloth to prevent the beans from falling through.
- Add the swollen soybeans to the basket.
- Carefully place the steamer basket with soybeans into the kettle.
- Cover the beans with the kitchen cloth and place a lid on the kettle.
- Let it steam on low heat for around 4 hours (adjust based on your preferred texture—steam longer for softer nattō).
- While the soybeans are steaming, boil some water and rinse the following items thoroughly:
- Spoon
- Ladle
- Tablespoon
- Storage containers (for fermenting nattō)
- Small dish (for mixing the nattō starter)
- Toothpick
- Let everything air-dry completely before use.
- For preparation, make sure you have the thermo box, hot water bottles and a towel at hand.
- In a small dish, prepare the nattō starter.
- Mix 50 g of store-bought nattō (or nattō from a previous batch) with 8–10 tablespoons of boiled water in the small dish.
- Stir well to ensure the starter is evenly distributed.
- Work quickly for this step!
- Transfer the steamed soybeans into the disinfected storage containers.
- Don’t overfill—each container should have only 2–3 layers of soybeans to allow proper fermentation.
- Pour the starter mixture evenly into all the containers.
- Mix thoroughly to coat all the beans with the starter.
- Cover the containers with plastic wrap
- Poke small holes into the plastic wrap with a toothpick to allow oxygen flow.
- Press the plastic wrap firmly onto the beans
- This helps to keep moisture levels stable during fermentation.
- Fill hot water bottles with boiled water.
- Insulate the thermos case by placing a towel inside.
- Carefully place the containers inside the thermos case and arrange them so that air can circulate around them.
- Add the hot water bottles into the thermos case
- Cover everything with the towel and close the thermos case with the lid.
- Place the thermos case in a safe spot and keep it there for 32-45 hours. The longer the fermentation, the stronger the flavor and stickiness. We have found 36 hours works the best for us.
- The temperature inside the thermos case should stay at least 40°C (104°F) for the entire fermentation period.
- To maintain this, you’ll need to replace the hot water in the bottles every few hours. We did it every 9 hours.
- Remove the nattō from the thermos case.
- Transfer the containers to the fridge.
- Let it rest in the fridge for at least 12 hours before eating.
- This helps develop the flavor and improves texture.
- Prepare the sauce (optional but recommended!)
- In a small dish, mix together:
- Soy sauce
- Mirin
- Dashi
- A small amount of water
- Adjust the ingredients to taste.
- Mix your sauce and nattō together, and your ready to enjoy!
- Serve it over warm rice with a bit of sauce and toppings like spring onions or kimchi.
Making nattō at home might seem like a long process, but once you get the hang of it, it becomes a simple routine. Plus, the reward is fresh, delicious, and affordable nattō that you can enjoy every day!
If you try this method, please let me know how it works for you in the comments! 😊