Natto (fermented soybeans) (納豆)

Natto is a Japanese food produced by fermenting soybeans with bacillus subtilis natto. Today, when we simply say 'natto' it generally refers to itohiki-natto (sticky natto). For types other than itohiki-natto, refer to the corresponding section.


Natto is eaten throughout Japan, but it was not consumed as much in the Kinki and Shikoku regions before. As a result of the reduction in odor achieved through the improvement in manufacturing methods and bacteria, and partly due to the TV and other media reports regarding the health benefits of one of the components of natto, 'nattokinase' natto came to be consumed in nearly all parts of the country since the latter half of the 1990s.

July 10 is designated as 'Natto no Hi' (day of natto). This was determined by Kansai Natto Kogyo Kyodokumiai (Kansai Natto Processors Cooperative Association) in 1981, which made a sound connection (nat (= 7) to (= 10)) in order to promote the consumption of natto in the Kansai region.
In 1992, Zenkoku Natto Kogyo Kyodo Kumiai Rengokai (National Federation of Natto Processors Cooperative Associations) formally designated the 'Natto no Hi.'
However, as 'natto' and 'natto jiru' (miso soup with natto) are the season words for winter for haiku (Japanese seventeen-syllable poem) and also as there is a proverb saying that 'in the natto season, there is no need for a doctor,' winter had been the season for natto. Thus there are objections to designating July as the time for Natto no Hi.

Nutrition and effects

As natto is rich in vitamin K which is vital for producing blood coagulation factors and the protein derived from soybeans, the food is still considered as an important source of protein. It has been included in the research items of the national price-statistics survey conducted by the Bureau of Statistics of the Ministry of Internal Affairs and Communications. Natto is also abundant in dietary fiber; in fact, 100 grams of natto will contain 4.9 to 7.6 grams of fiber. Dietary fiber is, along with oligosaccharide, etc., among the so-called prebiotics which are useful for the intestinal environment. Bacillus subtilis natto is a probiotic and is also considered useful for the intestinal environment. It is known to function as an antibacterial against O157.

Natto contains an enzyme that dissolves blood clots, and it has been confirmed that when a person eats natto, an FDP which is a cracked component resulting from the dissolution of clot increases in his/her blood.


Originally, natto was produced in nassho (temple storage) as a vegetarian dish, and this is how the name originated.

It is said that originally "natto" meant stored soybeans and "tofu" meant fermented soybeans and at a certain point those names were exchanged; this theory, however, is just a popular saying that emerged during the modern era. The character '腐' in Chinese word tofu doesn't mean "to go bad"; instead, it refers to curdled food such as cheese (corresponding to "curd" in English).

Production method

The traditional method for producing natto is to enfold the steamed soybeans in a rice-straw wrapper, maintain the temperature at around forty degrees and leave it for approximately one day. Rice straw naturally contains the bacillus subtilis natto, which is supplied to the soybeans, the fermentation occurs and natto is done.

In recent years, in order to meet the requirements of mass production, or because of the difficulty in obtaining good-quality straw for the traditional method, the mainstream practice has been to use pure cultured bacillus subtilis natto. In other words, steamed soybeans are packed in formed polystyrene or paper containers and a dispersion liquid containing pure cultured bacillus subtilis natto is sprayed onto them. If it is kept at the appropriate temperature, the bacillus subtilis natto increases and fermentation will occur. Natto is packed and shipped in a package which has an expiry date and brand indication when it reaches the appropriate degree of fermentation taking into consideration the progress of fermentation during transportation.

Natto and its hygienic aspects

Regardless of the manufacturing method, in order to produce natto as a business, permission from the governor of the prefecture is necessary under the Food Sanitation Act.

The bulk of natto on the market is produced through a manufacturing method in which pure cultured bacillus subtilis natto is used as seed.

Although the volume is very small, natto produced through the traditional method in which rice straw is used is still distributed. In this manufacturing method, bacillus subtilis natto is adhered to straw as a spore that's highly resistant to heat. If it is dipped in boiling water of 100°C for a few minutes, most of the sundry germs will boil and die, but the spores of bacillus subtilis natto will survive. The boiled soybeans are then placed in contact with the straw and the temperature is maintained in the range of 37 to 42°C, whereupon the bacillus subtilis natto germinates from the spores and starts to increase. Additionally, given its active propagating power, the bacillus subtilis natto consumes nutrition materials ahead of other sporular bacteria that have survived, thus preventing the increase of other microorganisms.

At any rate, the commercialized products that are distributed in Japan can be understood as being manufactured under control sufficient to satisfy the food standards.

When attempting to produce natto at home, several precautions must be taken. Bacillus subtilis natto is rather weak against acid, and sometimes its activity is hindered by the lactic acid produced through the activity of lactobacillus. Also, a less active bacterial strain is used for natto with less odor which has become popular as a result of technical development, and such natto may consequently let sundry bacteria grow depending on the environment. Bacteriophage (viruses that infest bacteria) is a natural enemy of bacillus subtilis natto, and sundry bacteria may increase after the phage became active. Sundry bacteria can proliferate quite easily especially in the case of boiled soybean before the increase of bacillus subtilis natto. Even if it is home-made for the home consumption, some consideration needs to be given for hygienic aspects.

In certain cases, people who don't like natto call it 'rotten boiled soybeans,' and so on. However, the difference between rottenness and fermentation is based on the value judgment as to whether or not the result of the action of microorganisms is harmful (fruitless) or useful. Therefore, natto is an excellent 'fermented food' because it is produced as a food in a sufficiently sanitary manner, is enjoyed by many people (although it may be only a part of the world), and has high nutritional value.

If bacillus subtilis natto, which forms highly heat-resistant spores and has an active propagating power, is mixed into steamed rice in the process of producing sake (a Japanese liquor), it may increase faster than Aspergillus oryzae and neutralize the latter. In such a case, bacillus subtilis natto becomes an unwanted sundry bacterium that generates sticky rice malt. This is the reason why eating natto is prohibited for sake brewing professionals during the preparation period for the sake brewing.

How to eat natto

The most typical way to eat natto is the so-called natto gohan (literally, boiled rice with natto), in which one eats it along with steamed, polished rice. Generally, natto is combined with soy sauce or another type of sauce and mustard. The mixture is stirred until sticky threads appear before eating. It is often eaten mixed with various foods such as egg of hen or quail, leek, Japanese ginger, grated daikon radish and katsuobushi (small pieces of sliced dried bonito). It is known that in some areas natto isn't served over cooked rice but is eaten independently. It is also known that in some parts of Hokkaido and the Tohoku region, sugar is added to natto.

Leek and mustard are considered as excellent condiments for natto because they can reduce its ammonium smell. Some say it tastes better if leek or mustard isn't added while stirring but small quantity of them are placed on the top after stirring, similar to the manner of adding leek or wasabi (Japanese horseradish) when eating soba (buckwheat noodles). Some people who don't like the smell of natto use wasabi instead of mustard.

In order to enjoy eating natto, it is important to knead it sufficiently. This is because the excessive moisture could prevent the generation of the sticky substance that includes glutamic acid (umami ingredient) if sauce is added before stirring. Although there is a groundless belief that if it's stirred approximately 100 times the polyglutamic acid can be changed into glutamic acid, changing polyglutamic acid into glutamic actually does not take that much stirring.

Natto is also used as a topping for Japanese-style spaghetti, an ingredient for okonomiyaki (savory pancake with various ingredients), or a topping for curry and rice or ramen (Chinese soup noodles). Natto jiru, which is prepared by adding finely chopped natto to miso soup, was eaten more often that natto gohan during the Edo period.

Because cooking natto with heat can cause a stronger odor, some favor cooked natto but others don't. However, in the case of natto tempura, a considerable proportion of the odor disappears by being deed fried and by the coating of batter, so it becomes easier to eat.

Selling method

Although the number has decreased in recent years, traditionally peddlers called 'natto uri' used to sell natto on the road. The peddler's cry was 'Natto, natto, natto; natto, natto, natto, i' (with a rise in pitch at the end).

Today, while natto is mainly sold in supermarkets, sales through automatic vending machines have increased. In Ibaraki Prefecture and Kawagoe City, Saitama Prefecture, natto is sold as souvenir (local specialty).

Packaging method

The traditional packaging methods were wrapping natto in warazuto (straw wrapper) used in the manufacture of natto or wrapping in kyogi (paper-thin sheets of wood).

Since 1960 and onward, foamed polystyrene containers have generally been used, because such packaging facilitates efficient shipping and distribution. Formed polystyrene containers are formed so that they can be stacked up, and in many cases they're sold in sets of two to four. A method has been devised to make the bottom of container hubbly so that it is easier to stir the natto in the container until threads appear.

The popularization of foamed polystyrene containers has helped achieve a dramatic increase in the consumption of natto. Compared to rice straw, however, it is less permeable and absorbs less odor, and the unique odor tends to become stronger. Because of such difference in flavor and for the purpose of showing the image of a 'natural food,' rice straw and kyogi are used even today for certain high-class products, nature-oriented products and souvenirs.

Currently, mustard and sauce for natto are usually attached to the natto package.

In 2008, Mizkan launched products packed in an improved type of foamed polystyrene. In this product, instead of attaching a conventional bag containing a liquid sause, a jellied sauce is directly injected into a small space in the container. Through this arrangement, the film that would otherwise separate the natto and the bag of sauce is eliminated, thus improving the permeability and making it easier to mix the sauce with the natto. However, it is disadvantageous in that it can't be transported or stored for a long period with the container in a tilted state.


In addition to the types described below, natto can be classified according to the soybean grain size, and large-size soybeans are generally preferred in the Tohoku region. There are certain types of natto with local features including shio natto made and eaten in Sakata City, in Yamagata Prefecture, which is a type of natto seasoned with salt, konbu kelp and other ingredients, and also Kinzanji natto in Kumamoto Prefecture, which is a type of natto made of soybean, wheat and salt, and seasoned with konbu kelp and ginger.

Shiokara natto (soybeans fermented with komekoji (mold grown on rice) and salt) (tera natto (natto made in a temple))

Today, if we mention natto we refer to the so-called itohiki-natto (sticky natto), which is produced by fermenting bacillus subtilis natto. There is also a type of natto called shiokara natto (tera natto), which is made by fermenting soybeans with Aspergillus oryzae, and drying it and then letting mature. Natto produced by koji mold was found in ancient Chinese remains uncovered in or around the second century B.C. In Japan there were two types: enshi (later shiokara natto) and tanshi (which vanished into history after the Heian period), and they are believed to be shi (pronounced as "kuki" in Japan and the kanji "久喜" was also used for the word) which is deemed to have been introduced in around the Nara period. They were not used independently but together as seasoning agents.

The word shiokara natto can be found in the literature from the Heian period, but it is thought that it spread among the general public in the Muromachi period and afterward. Around that time, itohiki natto also appeared and, in order to differentiate itohiki natto from shiokara natto, shiokara natto came to be called as kuki and itohiki natto as natto. Also during this period, since priests who visited the Northern Sung and Southern Sung dynasties brought back shiokara natto in Japan again and it spread in the country, it also became known as tera natto. Even today, Daitokuji natto (natto made in Daitoku-ji Temple), Tenryuji natto (natto made in Tenryu-ji Temple), Ikkyuji natto (natto made in Ikkyu-ji Temple) and Hama-natto (Hamana natto (soybeans fermented with komekoji (mold grown on rice) and flour, pickled in saltwater and dried)) are still produced.

Hikiwari natto (crushed natto)

Natto made with ground (hence "crushed") soybeans
It is often used for natto jiru. It is said that it ferments more quickly natto and is easier to be digested than the usual natto. In contrast to hikiwari natto, the usual natto, for which non-ground soybeans are used, is called 'tsubu natto' (whole-bean natto).

This technique had been used in Akita Prefecture since the old times, and it is said that Yamada Foods first introduced it throughout the country. According to Yamada Foods, each grain is divided into approximately six parts. Yamada Foods also sells 'kizami natto' (literally, minced natto) for which a grain is divided into approximately fifteen parts.

Soboro natto (natto mixed with kiriboshi daikon (thinly sliced and dried strips of daikon))

A specialty of Ibaraki Prefecture
It is also called oboro natto or shoboro natto. Soboro natto is prepared by mixing minced kiriboshi daikon in natto and adding a seasoning agent such as soy sauce. It is eaten as nibbles for drinks or with rice.

Hoshi natto (sun-dried natto)

A specialty of Ibaraki Prefecture
Natto has been dried in the sun so that it would keep for a long time. Even if natto is dried, the bacillus subtilis natto will not die out. It is eaten as it is, or by reconstituting with hot water or together with ochazuke (boiled rice with tea poured over it).

It is said that hoshi natto was originally prepared as a preserved food, but today it is brought with when traveling to overseas destinations where natto is unavailable.

Age natto (fried natto)

It resembles hoshi natto, but it is prepared by frying natto in fat or oil in order to eliminate the stickiness. The characteristic odor of natto isn't too strong. Special manufacturing technique is used so that bacillus subtilis natto doesn't die out even when deep fried. It is usually eaten as nibbles for drinks without cooking. It is seasoned with soy sauce, salt, umeboshi (pickled "ume," or Japanese apricot) and/or ground red pepper. it is served as a snack on the international flights of Japan Air Lines.

Shio natto (natto made in Kochi Prefecture, fried with salt and rice bran)

A local dish in certain parts of Kochi Prefecture
Natto is sprinkled with salt and bran and then parched with an iron pan. In the traditional manufacturing method, steamed soybeans (instead of natto available on the market) are placed in rice husks and used once the threads become noticeable.

Ama natto (sugared red beans)

It is quite different from the above-mentioned natto, which is a fermented food; ama natto is a Japanese confectionery developed in 1857 by Eitaro. Initially, it was named amana natto, being modeled after hamana natto (hama natto). It was only after the Second World War that the name was shortened to "ama natto." In the Kinki region, the use of the word "natto" can sometimes refer to ama natto.

Akita Prefecture

There is a monument indicating 'Birthplace of Natto' in Misato-cho, Senboku-gun (Akita Prefecture). Also, in Akita ondo (folk song), 'hiyama natto' (natto from Hiyama, in Akita Prefecture) (the Hiyama district of Noshiro City) is mentioned as one of specialties of Akita.

Mito City, Ibaraki Prefecture

Since the Meiji period, in keeping with the opening of the railway (Mito Line), natto has been sold as a souvenir (it is said that the first one was Tengu natto), and this area is famous for the production of natto. On March 10 (day of Mito) of each year, 'natto hayagui taikai' (literally, a competition of eating natto quickly) is held.

Kumamoto Prefecture

As an exceptional case, natto has been widespread in Kyushu since the old times. It is said that because there is a legend that, at the time of the Bunroku-Keicho War, Kiyomasa KATO loaded wet soybeans onto the back of a horse which fermented because of high body heat of the horse, and became natto. There is a natto manufacturing company that operates on a national basis (e.g. Marumiya). Also, natto is regularly sold in supermarkets, so the consumed amount is impressive.

Generally speaking, the amount of consumption is greater in eastern Japan, particularly in the area from northern Kanto to southern Tohoku. Ibaraki Prefecture is the top producer, and Fukushima Prefecture is the top consumer. It is understood that in western Japan (especially the Kinki region) people do not eat natto often, and the amount of consumption is smallest in Wakayama Prefecture. However, in recent years about ten different brands of natto products are sold in supermarkets in the Kinki region, and the amount of display space has become nearly equal to that of the Kanto region.

Natto overseas

In the U.S. state of Hawaii, which is home to large numbers of Japanese-American immigrants, local tofu manufacturers actually produce and sell natto.

In the following regions, soybean-based fermented foods similar to natto are sold.

Southern Asia, covering Nepal at the base of the Himalayas and the area from China's Yunnan Province to Southeast Asia

Korean Peninsula: 清麹醤


In the cultural program 'Hakkutsu! Aru Aru Daijiten' (Encyclopedia of Living) broadcasted by Kansai Telecasting Corporation and Fuji Television Networks, Inc. on January 7, 2007, it was announced that natto was effective for dieting. As a result, many consumers bought lots of natto and caused a temporary shortage of supplies. However, it was later revealed that the data introduced in the program was a fabrication.

[Original Japanese]