Around the 1640's, Edo and around Edo which was one of the places where soy-sauce was consumed the most because of its large population, the idea of 'koikuchi soy-sauce' which took a year to make came out.
1640年代頃、寛永年間、巨大な人口を抱えて醤油の一大消費地となっていた江戸近辺において、1年で製造できる「こいくち醤油」が考案された。