Kimoto is the original method of sake-making where lactic acid is not added when creating the yeast starter, and is instead allowed to naturally develop on its own. Because the lactic acid must grow on its own, this process takes longer. This creates a sturdy starter, resulting in a robust, earthy and sometimes funky brew.
Yamahai is a method similar to kimoto, allowing lactic acid to grow on its own. The main difference between the yamahai and kimoto method is that the steaming rice is not macerated with a stick. Yamahai sakes are prized for their rich flavor profile, high in umami and rice flavor.