When was the first natto produced? Unfortunately, there is no definitive answer, and the sources of its origin vary. One source gives credit to Shotoku Taishi (574? A.D.--622 A.D.), Empress Suiko's regent who facilitated the promulgation of the first written set of laws, the Seventeen Article Constitution, and who built Horyuji temple, Japan's first UNESCO World Heritage Site. Another source attributes the first natto production to Hachiman Taro Yoshiie (Minamoto Clan, 1039--1106), the ancestor of Minamoto no Yoritomo (1147--1199), who established the Kamakura Shogunate and ruled Japan as a samurai in place of the emperor. Nonetheless, the one point that all sources have in common is that natto was made by "accident" from boiled soybeans preserved in straw.
For soy beans to make their transformation into natto, they need just the right temperature and humidity, and of course, the bacillus natto, a bacterium discovered in Japan that grows in the country's unique climate. Bacillus natto is found naturally almost anywhere, but it propagates most abundantly in straw (dried stems of rice or wheat; may be woven into rope, bags, barrels, etc.). In the old days, natto was wrapped in straw, a method still employed by some manufacturers today. It is said that rice farming was brought to Japan from China toward the end of the Jomon Period (circa 400 BC), and the harvest of soy and other beans is said to have started in the following Yayoi Period. Since the mud tools of that era were fragile, people must have had to crumble and then boil the hard soybean. And in their dwellings, they used to line the floor with straw and dried leaves for warmth. "Boiled soybean" and bacillus natto-rich "straw"... It is not difficult to imagine how natto was accidentally produced.
In the old days, farmers used to make homemade natto for their personal consumption, but by the middle of the Edo Period, there were "natto vendors" who walked around town selling their products from the break of dawn. However, the function of the bacillus natto was not yet understood in those days, so natto was consumed only during the fall and winter months, when the bacterium grew readily. Today, after much research has been conducted on the bacterium, natto manufacturers add cultured bacillus natto to soybeans in order to provide Japanese consumers with "fresh" natto all year round. The latest figures show that over 700,000 tons of natto are produced annually.