I have recently embarked on a new journey, making Sake. Something that I have been thinking about for several years, but had always considered to be too complicated for a non-Japanese speaker. However, two things changed my mind. One was the discovery of the excellent book Brewing Sake, Release the Toji Within by William G Auld, which demystifies the process enormously, and the other was discovering that at least one traditional Sake process uses the same microbiology as sourdough! And it is the latter discovery that leads to me including my first Sake brew in a blog on a sourdough website.
I won’t go into too many details on the history and production of Sake, there are plenty of other websites out there that do that already, but the important thing to note is that Sake is brewed like a beer rather than fermented like a wine. This is because unlike grapes, rice does not contain simple sugars that can be converted into alcohol by yeast, but contains starch, which must first be broken down into glucose and maltose by the action of enzymes. In the brewing of beer this is achieved by the action of malt amylases during the mashing process; in the brewing of Sake it is achieved by the action of amylases, enzymes produced by the fungus Aspergillus oryzae, otherwise known as the Koji-kin.
At a basic level, Sake is the product of two microorganisms, Aspergillus oryzae and Saccharomyces cerevisiae (brewer’s yeast) working in tandem. Whereas in grape fermentation all of the sugar is available at the start, in Sake fermentation the sugars are produced continuously by the action of the koji enzymes on the rice starch. It is this gradual provision of sugars that allows the yeast to operate at higher alcohol levels than are normally encountered in wine and beer making.
So where does the sourdough process come into this? Well, in the 14th century a group of Bodaisen Shoreki Ji Buddhist monks developed a Sake brewing process, called the Bodai moto, which started out with a mixture of polished rice, cooked rice and water that was left out in the open air to become ‘infected’ with lactobacilli and wild yeast. Once the rice starter had begun to ferment, the lactic acid-rich hooch, known as the soyashimizu, was poured off and used in the main mash along with the steamed rice and koji. The results depend on the fermentation of the mash with wild yeast and can be unpredictable, and the method died out around 1925. However towards the 1990s a group of brewers from Nara reintroduced the procedure, and had the soyashimizu introduced into the moto rather than the main mash, relying on cultivated yeast to carry out the main fermentation.