Soku (first) jo (brew) moto (starter) is a very simple method of starting sake and preventing contamination. First of all, water, lactic acid, koji and yeast are mixed at the temperature of 10-12℃, then mixed with steamed rice. The temperature is slightly higher than used for ki-moto and yamahai-moto. Thanks to the higher temperature, saccharification and yeast cultivation are faster than other methods. It takes about 14 days to reach full yeast cultivation.
This method was invented at the National Institute of Brewing Research (Shurui sougou kenkyusho) in 1910. Despite its simplicity (and cost effectiveness due to reduced labor), it brings a clear and smooth, low umami flavor, so is widely used among most sake breweries.