The Main Ferment – Moromi

Discusses the main fermentation stage of the sake brewing process, moromi.

Once san-dan-jikomi is complete and the final addition has been made we enter into moromi. Moromi starts the day after the final addition, which is tomezoe. It lasts until fermentation is almost complete. This can take anywhere from 2 weeks to about a month.

The time needed for moromi is based on both temperature and koji characteristics. In particular the characteristic diastatic power the koji can muster at the moromi temperature.  The yeast work faster at the low temperatures of moromi than do the koji enzymes.

At the end of the moto the alcohol content was anywhere from about 5% to 10%. With the san-dan-jikomi additions the concentration of alcohol was also cut in the same way as the yeast and acid. However, as some yeast has been reproducing some have been producing alcohol. So by the start of moromi we have regained much of the alcohol concentration we had at the end of the moto. Continue reading “The Main Ferment – Moromi”

Sake Yeasts

Discusses yeast, sake yeast and what yeast need to do a good job fermenting.

Yeast: a single cell fungus whose activities have been known to man for far longer than we have known about yeast itself. We have evidence of yeast being used as far back as four thousand years ago in Egypt. They used yeast for both baking and brewing. Wine was also present in this period.

In 1857 Louis Pasteur proved that fermentation was the results of living yeast rather than a chemical reaction. In this work, Pasteur showed that as oxygen is added the growth of the cell count increases and fermentation slows. Not only did this show the significant of yeast but also its two distinct modes of operation: the aerobic and the anaerobic. In the aerobic mode, yeast reproduce by budding, a process of a child cell being created and split off from the parent cell. The anaerobic mode proceeds with little to no growth in the number of cells but with increased alcohol and CO2 production. Alcohol and CO2 are produced in equal amounts based on the following formula:

C6H12O6 -> 2 C2H5OH + 2 CO2 Continue reading “Sake Yeasts”

Sake Yeast Mash – The Moto

This article looks at the three types of Sake yeast mashes, also known as moto and shubo. The differences between these three moto are examined.

Moto (元), Shubo (酒母), Yeast mash are all names for the Sake yeast starter. In this article I will only use the term “moto” but the three can be used interchangeably. Moto is where the number of yeast cells is increased to the needed level. The moto is used to inoculate the main sake fermentation, the Moromi (諸味). To build the moto we start with rice (米), koji (麹) and yeast (酵母). These three ingredients along with water were the only ones used for moto originally. The method to produce this original moto is known as Kimoto. It features a vigorous mixing, taking many hours, to produce a puree of the ingredients. It was thought this vigorous mixing, called Yama-Oroshi, was needed for the ingredients to properly work together.

In 1909 a modification to the Kimoto method was developed. The modification was to drop the vigorous mixing. As it turned out, the mixing was not really needed. The modified process was called Yama-Oroshi haishi moto or Yamahai moto for short. Continue reading “Sake Yeast Mash – The Moto”