Yeast starter, starter (seed) mash

The initial stage of brewing, dedicated to the growth of the yeast fungi that produce the alcohol which is the objective of moromi fermentation.   As sake quality is closely related to yeast quality, the handling of the yeast starter has long been considered to be a foundation of sake brewing, and great attention has been paid to the propagation of large quantities of good, pure sake yeast in shubo.

Lactic acid plays an important role in preventing contamination by unwanted micro-organisms and ensuring the growth of yeast alone. There are two schools of shubo, the kimoto school in which lactic acid bacteria are propagated during the early stages, and sokujo (“quick-fermenting”) school, which sees lactic acid added to the mash at the outset. This includes ko-on- toka shubo (high temperature saccharification shubo), in which the raw materials are sterilized by high temperatures before yeast is added. Today, the quick-fermenting school using lactic acid is most widespread.

Shubo and moto are synonyms.   Moto (implying “origin” or “”base”) is the older term, but, as it is not a general-use character but only used in a sake context, the use of shubo has become more common. Shubo is written with the characters for “sake mother”.