Without Koji, sake would not be with us today in its current form.
Rice is a grain just like barley but since it’s polished, removing the germ (the reproductive part that germinates to grow into a plant), it is unable to go through a malting process that beer does. As a result, a different approach using this mystery mould is required.
Koji is actually the term for the rice that has been inoculated with Koji-kin (a mould, micro-organism or fungus usually in a powder form). This magic mould is also used to make soy sauce and miso (fermented bean paste) but also other alcoholic beverages, namely Shochu, Japan’s other national beverage. This is a distilled beverage made from sweet potato (imo), barley (mugi), and rice (kome) that has an alcohol content of around 25%-30%.
Koji-mould is cultured in steamed rice to produce this Koji rice which takes around 48 hours in a room with wooden panels. This is called a koji-muro comparable to a sauna, where the temperature is around 32 degrees. Around 20% of the steamed rice will be allocated for the Koji rice, the rest will be added to the tank in batches, usually over 3 days.
The process of making koji has several stages and is quite intense, not too dissimilar to looking after a newborn baby with a need for it to be check every few hours, and monitoring the temperature and growth (ok, that last part doesn’t apply to a baby). The mould on the rice grain needs to have even growth so requires the clumps to be broken up usually by hand. Some brewers however, are automating the process but where’s the fun in that. There’s nothing better than digging your hands into some koji rice, it borders therapy. Once there is sufficient growth, this furry looking creature is added to the starter with steamed rice, water and yeast. The Koji supplies the shubo (fermentation starter) and moromi (main mash) with enzymes to convert the starch in rice to sugar so that the yeast can convert this to alcohol.
There are three varieties of Koji mould with yellow Koji-kin, scientifically known as Aspergillus Oryzae, being the default option for sake brewers. There are brewers out there such as Niida Honke from Fukushima prefecture with their Odayaka range, who break the mould (pun intended) by using a different strain. They use the Shochu variety (Shiro-koji or white koji-kin) which brings out more citric acidity, comparative to wine as oppose to the standard lactic tones.
There are sake styles where the percentage of rice used for Koji is increased from the standard 20% creating a richer style of sake. One that springs to mind is ‘Tamagawa Time Machine’, which resembles and I quote from their website “rich aromatics resemble Madeira or port wine, with tangy dried fruit notes like a sherry-laden fruitcake or well-matured christmas pudding.”
In an industry that is steeped in tradition and history that can sometime hold you back, you have to admire those experimenting with alternative brewing methods.