AN INTRODUCTION TO SAKE
KOJI 麹 :
MAGICAL MOLD
KOBO 酵母 :
MOTHER OF FERMENTATION
Koji-kin (麹菌), or in scientific terms Aspergillus
Oryzae, is a type of mould spore that has been
a foundation for the fermenting food culture of
Japan for many years. It is a beneficial and safe
variety of bacteria used for miso, shouyu (醤油, soy
sauce), sake, mirin (味醂, sweet sake for cooking),
rice vinegar, shochu and various other ingredients
in Japan.
Yeast or kobo (酵母) in Japanese plays a critical
role in determining sake quality. Until the early
twentieth century, sake was made using naturally
occurring yeast. Over the decades, technology has
improved and there are more and more methods
of purely isolating and selecting yeast from the
main ‘mash’ or moromi, (醪) of a brewery that has
produced good sake. Many breweries have their
own ‘prosperity yeast strains’ which were discovered
by and exclusive to them.
Grape juice contains sugars which ferment in the
presence of yeast, but with beverages made from
grains such as sake and beer, it is first necessary to
use enzymes to break down the starch in the grain
to convert it to sugar before yeast fermentation.
In beer brewing, malt is used as the source of
these enzymes, but for making sake, ‘kome-koji’ (
米麹) is the key player. Kome-koji is steamed rice
inoculated with koji-kin, and it creates enzymes
that convert rice starch into sugar, which the kobo
(酵母, yeast) feeds on.
Koji also produces the other type of enzyme that
breaks down protein and produces amino acid and
peptide, which creates the unique characteristics of
each sake. Koji production is the heart of the sake
brewing process, and this process is most exercised
in the mind of master brewer. It requires constant
control and adjustment of temperature throughout
its 40-48 hour process in koji-muro (麹室), a special
temperature-controlled room and traditionally
covered with cedar wood with an electric heating
wire or convection heater. In modern settings more
and more stainless-steel covered koji-muro can
be seen. The koji itself releases heat and the koji
temperature has to be checked every two hours
during the day and night.
Since 1906, yeast selected in this manner has been
distributed largely and widely by the Brewing
Society of Japan as Kyokai-kobo or Brewing Society
Yeast (協会酵母). Kyokai-kobo is numbered, and
packed in ampules. Currently, the most widely
used yeasts are Sake Yeast kyokai #6, #7, #9, #10,
and #14. Each produces its own aroma and taste
characteristics and the specific choice depends on
the desired sake quality. More recently, brewers
have been utilising microbial technology to produce
yeasts designed to increase the amount of esters
delivering a fruity aroma.
Since the 1990s, numerous yeast strains produced
by several prefectures with advanced area of study
have appeared in the market such as Shizuoka kobo,
Yamagata Kobo, Akita Kobo and Fukushima Kobo.
AN EXPLORATION
The world of sake is full of contradictions and
surprise, and we hope that through the Museum of
Sake Journal we can help with the understanding,
exploration and enjoyment of this fascinating drink.
MUSEUM OF SAKE JOURNAL 9