Behind the Fermentation of Natto
- Chelsea Tan
- 9 hours ago
- 3 min read
Natto is a traditional Japanese breakfast food made of fermented soybeans.
It’s typically eaten mixed with karashi mustard and tare sauce, served on top of a bowl of rice. It is often called an acquired taste, especially for foreigners who didn’t grow up eating it. This is because of natto’s two main off-putting factors: scent and texture. Natto has a strong, funky aroma that many people find unpleasant, as well as a sticky, slimy, and stringy texture. As for the taste, natto has a slightly bitter flavor with a strong umami taste.
The origins of natto are unknown, but it is likely that, like other fermented foods such as cheese, wine, and beer, it was created accidentally or as a means of food preservation. One popular legend in Japan about the origins of natto dates back to the Gosannen War. A samurai and his army were resting at a farm, eating boiled soybeans and rice during their conquest of Japan. As the enemy approached, they retreated and quickly wrapped their food in rice straw.
This rice straw is a natural source of Bacillus subtilis, a bacterium that ferments soybeans. Fermentation is when microorganisms (bacteria, yeast, or fungi) convert carbohydrates (sugar and starches) into acids, gases, or alcohol. For this to occur, the bacteria need a warm, humid climate. The army accidentally created this environment through the heat and sweat of their horses during their escape. This allowed the bacteria to consume and digest the natural sugars and proteins inside the beans, producing a sticky web of glutamic acid (an amino acid) and fructan (a sugar), giving natto its signature stretchy strings.
Today, although some traditional natto companies still use rice straw to make natto, most use styrofoam containers instead. Additionally, natto is now made in a more sterile environment. To make it, companies start by soaking and boiling dried soybeans. After that, they add a natto starter culture (Bacillus subtilis) and incubate the beans for 12-24 hours in a warm, moist environment to ferment. Once fermentation is complete, natto is stored in the fridge to stop the fermentation.
Unlike other popular Japanese foods like ramen and udon, natto is widely unknown outside of Japan. However, in recent years, it has gained popularity for its nutritional value and numerous health benefits. Natto contains many probiotics that benefit gut health, improve digestion, and prevent bloating and constipation. This is because Bacillus subtilis can survive stomach acid and reach your intestines alive, helping create a healthy environment for good gut bacteria and fight off bad ones.
Additionally, natto is good for bone health due to its high calcium content (~220mg/100g) and its record-breaking natural vitamin K2 content, which also supports heart health. Finally, natto is perfect for the growing demand for high-protein diets and meals, as it contains ~20g of protein per 100 g, which helps build, repair, and maintain muscle.
As natto continues to grow in popularity, don’t be dismayed at seeing its stretchy strings and smelling its funky scent for the first time. Remember: Natto might seem unpleasant at first, but its unique flavor, major health benefits, and long-standing history in Japan make it worth a try, even if it takes some getting used to!
Chelsea Tan is a rising senior at Dalat International School in Penang, Malaysia. Growing up across three countries inspired her to learn about foods from different cultures and the science behind them. She plans to study food science in college and has explored this interest through research, internships, and trying new foods across the world.
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