Generally, sake brewing season starts from October until May, but the main part of the season starts from December until February and this period or sake brewed during this period is often called kanzukuri (cold-weather brewing). The kanzukuri system was perfected by the middle of Edo Period around 1700-1750, but before that time, sake used to be brewed throughout the year. With the advancement of brewing technologies, seasonal brewing styles were devised, such as sake brewed from summer until early fall, and kanmaezake made in early winter. The one that garnered attention was kanshu brewed during kanzukuri. As kanshu was brewed in the coldest part of the year, the growth of contamination bacteria was inhibited, and it was easier to control the temperature of moromi (fermentation mash), so the sake brewed then was of the highest quality. Gradually, sake came to be brewed mainly in the coldest season. It is the off-season for farming and fishery, which may be one of the factors that made it easier to hire seasonal workers from other regions.
In fall, brewery workers who had returned to their hometown during summer time come back to breweries for work, and this is called kurairi. The first thing they do when they stepped into breweries is to create a clean environment for brewing, such as polishing and sterilizing the facility, and bailing all water out of the well and cleaning inside the well. Then they hold a sake festival at the breweries or shrines to pray for the safety and success of brewing season by receiving a purification ritual from Shinto priests.
On that night, most of the breweries have a customary gathering for a sake party since workers gather for the first time in a while. This is how sake brewing of the year starts.