Both names refer to traditional brewing techniques further explained below. The sake made in either ways have a similar tasting profile, with a deeper flavour, higher acidity, and distinct earthy, gamy, umami-driven notes. Nowadays, only about 1% of sake production is done with the kimoto method, and 9% with the yamahai one!
KIMOTO (Japanese: 生酛)
Also known as kimotozukuri (生酛造り), it is the historical predecessor of the yamahai method. Rice and water are mixed by the brewers themselves with oar-like poles for hours, in an extremely time-consuming process. Moreover, ambient lactic acid bacilli are used for the fermentation starter (shubo).
YAMAHAI (Japanese: 山廃)
Also known as yamahai-shikomi (山廃仕込み), this method was introduced in the beginning of the 20th century. As for kimoto, the brewers use ambient lactic acid bacilli for the fermentation starter. However, it does not involve the exhausting pole-ramming process.