Until the middle Jomon Period, our ancestors primarily ate fish, shellfish, flesh meats and minor cereals. It was in the latter part of the Jomon Period that rice farming was introduced from around the lower the Yangtze River in China into the northern parts of Kyushu, which is now the towns of Itazuke, Fukuoka prefecture and Nahatake, Saga prefecture.
Before long, rice farming spread throughout Japan, replacing millets and other minor cereals to firmly establish itself as the staple food of the country. It is still our staple diet and there are sufficient reasons behind this.
It is said that the main producer of the rice plant is the evergreen forests (silva zones of broad-leaved evergreen forests growing within the subtropical zones to the temperate zones) covering the areas from the province of Yunnan, China to the East Indian region of Assam. Nevertheless, since the rice plant originated as cereal plants growing in marshy regions, it suited the hot and humid climate of Japan.
Moreover, it yielded large harvests, and furthermore, they tasted good. It seems natural that the Japanese people found it to their liking.
As rice established itself as the staple food for the Japanese, people made attempts to brew sake from it. Naturally, the method used was that of making sake from cereals, the "Kuchihami".
It is believed that the "Kuchihami sake" was introduced into Japan from the people growing root vegetables in southern Asia and until recently, it has been brewed as an offering in the festivals of Ainu people and also in the main and surrounding islands of Okinawa.
Since sake was used for the black magic and the religious ceremonies, it is believed that those who performed the "Kuchihami" procedure have been limited to virgin maidens or to "Miko", maiden spiritualists who serve God. (Contrary to this, in "Okuma Country Fudoki (the records of the culture and geography of the province)", it is documented that "men and women gathered around chewing rice in their mouths, spitting the chewed rice into a brewing vessel...")
In the Japanese language, the act of brewing sake is called "Kamosu (brew)" which is derived from the word "Kamisu (chew)".
When the rice is chewed, the starch in the rice acts with salivary amylase (diastatic enzyme) within the saliva, turning it into glucose. When the chewed rice is left in a pot, naturally occurring yeast in the atmosphere mix, fermenting and turning it into sake. This is the principle behind the process of making "Kuchihami sake".
In the latter part of the Jomon Period to the Yayoi Era (BC300-AD300), wet-rice agriculture spread from western Japan throughout the Japanese archipelago. People's lifestyle of the old, which depended on hunting and gathering, was transformed to the agricultural lifestyle with rice becoming their main diet. This marked the start of the Yayoi Culture.
Sake made from rice was readily brewed and became popular among the people.
One problem with "Kuchihami sake" was that it can not be made in large volumes at a time. Interestingly, in a 3rd century Chinese historiography, "Gishiwajinden", we find a passage which says "Wajin (Japanese people) of all ages and sex are hardy sake drinkers". The scene described was that of a gathering after a funeral ceremony so there must have been many people and likewise a large quantity of sake.
Could it be that a "rice sake" brewing technique beyond "Kuchihami" already existed at that time? In fact, a literature supporting this theory exists. In an early Nara Era ethnography, "Harimakoku Fudoki (records of the culture and geography of a province)", there is a story where, "the 'Mike' (the rice offering to the gods) offered on the household Shinto altar got moldy because of the rain so people brewed sake using the moldy rice, paid tribute to the gods, and held a banquet afterwards". This proves that the people had already discovered how to brew sake from rice malts. The origin of rice sake brewing is clearly evident here.