Sake (junmai)

Junmai-shu — 'pure rice sake' — is sake brewed only from rice, water, koji (Aspergillus oryzae-inoculated rice), and Saccharomyces cerevisiae yeast, with no added distilled alcohol. It is the canonical form of sake in the traditional sense; the various honjozo, ginjo, and daiginjo designations layer on additional specifications (rice polishing ratio, added alcohol presence) but junmai is the baseline.

Sake is microbiologically unusual: it is the only major commercial alcoholic beverage that uses parallel multiple fermentation. Beer and wine ferment a sugar-rich substrate (malted barley wort, grape juice); the conversion from starch to sugar happens before fermentation. Sake converts rice starch to sugar AND ferments sugar to alcohol simultaneously, in the same vessel, at the same time. Koji produces amylase enzymes that hydrolyze rice starch to glucose; Saccharomyces immediately consumes the glucose and produces ethanol. This is the most efficient saccharification-fermentation system in the brewing world and is responsible for sake's distinctive ability to reach high alcohol levels (18-20% in some traditional preparations) at low temperatures with high purity.

The technical complexity of home sake brewing is genuine. The koji must be produced or sourced (koji-kin spores can be ordered; the koji-making step takes 2 days with careful temperature control); the moto (starter) is a multi-stage process; the moromi (main mash) requires daily additions of more rice and koji over 4-7 days; the final fermentation runs 3-4 weeks at cool temperatures; pressing requires specialized equipment for any meaningful volume. Sake is one of the few traditional ferments where the home version is meaningfully more difficult than the commercial.

Sandor Katz's framing of fermentation as the work of communities of organisms applies particularly cleanly here: sake is two organisms (koji-mold and yeast) doing different jobs in the same liquid at the same time, dependent on each other — koji can't produce alcohol; yeast can't break down starch; together they make sake.