Natto Day (Nattō no Hi)

What Is Natto Day?

Every year on July 10, Japan celebrates "Natto Day" (Nattō no Hi). The date comes from a play on numbers: "nat" (7) and "tō" (10) combine to sound like "nattō." The anniversary was first established in 1981 by the Kansai Natto Industry Cooperative Association to promote natto consumption in the Kansai region, where eating natto was not yet common at the time. In 1992, the National Natto Cooperative Federation (Nattō-ren) re-established it as a nationwide anniversary. It is a day to take a fresh look at natto, a traditional Japanese fermented food.

A Food Said to Have Been Born by Chance

There are several theories about natto's origins, and no one knows for certain.

• Legends of Minamoto no Yoshiie and Prince Shōtoku: Legends in various regions tell of boiled soybeans left wrapped in straw, where natto bacteria from the straw multiplied and turned them into sticky, stringy beans. The best-known story says the Heian-period warrior Minamoto no Yoshiie discovered it by chance during a campaign in northeastern Japan.
• The origin of the name: The word "nattō" already appears in "Shin Sarugaku-ki," written in the mid-11th century during the Heian period. The leading theory is that the name comes from "nassho," the office in Buddhist temples that handled supplies, where natto was made.
• The street vendors of Edo mornings: In the Edo period, natto vendors walked the streets every morning, and natto became an everyday food for ordinary people.

Natto Bacteria and Nutrition

Natto is made by fermenting well-steamed soybeans with natto bacteria (Bacillus subtilis var. natto).

• What makes it sticky: The strings are made of substances such as "polyglutamic acid" produced by natto bacteria. The sticky part also contains an enzyme called "nattokinase," which has been the subject of various studies.
• Heat-resistant "spores": When conditions become harsh, natto bacteria form tough shells called "spores" and go dormant. Spores are so hardy they survive boiling, so when straw is boiled to sterilize it, only the natto bacteria survive — a fact long used in traditional straw-wrapped natto making.
• Rich in vitamin K: Natto contains soybean protein and plenty of vitamin K (K2). Vitamin K is a nutrient involved in blood clotting and bone formation. For this reason, people taking the blood thinner warfarin may be told to avoid natto.

Fun Facts About Natto

• Stirring makes more strings: The more you stir natto, the more strings form and the milder it is said to taste. Whether to stir before or after adding the sauce is a matter of personal preference.
• The white gritty specks: The white granules sometimes seen in older natto are crystals of the amino acid tyrosine. They form as fermentation breaks down proteins, and they are not mold.
• Sake breweries avoid natto: Because natto bacteria are hardy and multiply vigorously, sake brewers traditionally avoid eating natto during the brewing season to keep other microbes out of their fermentation.
• Another natto day: Nattō-ren also designates January 10 as "Itohiki Natto Day" (Stringy Natto Day), since 1 (i) and 10 (to) can be read as "ito" (string).
• "Natto" abroad: In recent years, natto has become known overseas as a Japanese fermented food rich in plant-based protein.

Tips for Enjoying Natto Day

• Stir your natto a little more than usual and compare the texture and taste.
• Try topping it with your favorite additions, such as kimchi, green onions, or raw egg yolk.
• Try a different type, such as hikiwari (chopped) natto, large-bean natto, or a regional specialty.
• Share the story of natto, said to have been born inside a bundle of straw, with family or friends.

A Thousand Years of Food Culture in Every Tiny Bean

July 10 is a day to appreciate natto, which has long supported the Japanese dining table. This sticky food, said to have been born from tiny bacteria in straw, has a history long enough that its name appears in Heian-period writings. Today, why not stir your natto a little longer than usual and enjoy its flavor anew?