- “House” yeast; “on-the brewery” yeast
In kimoto-school (kimoto and yamahai) yeast starter, a series of micro-organisms including nitrate reducing bacteria and lactic acid bacteria work in succession, with the result that finally yeasts which can grow in an environment made acidic by lactic acid take precedence in growing. In breweries where production has gone on for generations, yeast which has survived during the brewing process is found on floors and walls due to splashes from shubo, moromi, and so on. The yeasts particular to such breweries are called ie-tsuki-kobo (literally “yeast on (attached to) the house”). It is often said that breweries which have a long history of producing fine, mellow sake have superior “house yeast” in residence.
However contemporary brewing methodology generally sees the use of pure cultures of reliable yeast strains as distributed by the Brewing Society of Japan and others, so sake products showing information to the effect that they are made with ie-tsuki yeasts have become much fewer. Well-known examples include HY yeast ( Sakuramasamune Company, Limited ）, Kikumasamune Yeast ( Kiku-Masamune Sake Brewing Co.,Ltd. ）and Gokyo (long second “o”) Yeast ( Sakai Sake Brewing Co.Ltd. ）.