The Magic of Mould: Koji
We’ve covered rice and water - now it is time to introduce one of the most integral ingredients in sake brewing: koji. To put it simply - Aspergillus oryzae, or ‘koji’ to friends, is a type of mould that is used in sake brewing (along with many other fermentation processes), and is auspiciously known as ‘Japan’s national fungus.’
Before you grimace, it’s not the type of ‘bad’ mould that you hope never to find in your fridge. In fact, it is responsible for so many of the wonderful fermented products we all know and love - soy sauce, mirin and of course, sake!
Different types of koji
There are actually several types of koji used in fermentation processes for different types of Japanese alcohol. The main three are:
Yellow koji (ki-koji): The most common in sake brewing, known for its balanced enzyme production.
White koji (shiro-koji): Used primarily in shochu production, creates more citric acid.
Black koji (kuro-koji): Used in Awamori and shochu, it is also recognised for its citric acid production.
Each type imparts unique characteristics to the final product, but yellow koji remains the go-to for most sake brewers.
Why is it important? And fun facts!
In the world of wine, fermentation is pretty straightforward, yeast breaking down the easily accessible sugars in the grapes into ethanol (our trusty alcohol) and CO2. With beers, cereal grains have endosperm with enzymes on standby, ready to digest the carbs down into glucose. Normally, rice would have the same, however during the polishing process in sake, the outer husk and endosperm are removed, leaving no way to access the sugar. And with no sugar, the yeast is going to pack up the party and go elsewhere. To solve this issue, our trusty koji comes in to play. In very….very abridged terms, the rice is meticulously steamed for ideal koji mould enjoyment, cooled and transported to a special room and sprinkled with said koji spores. From here, the koji mould tunnels into the rice grains and releases its enzymes to make a meal out of it, and hey presto: we have fermentable sugars and other delicious yeast nutrients.
What does it do for flavour?
Koji's influence on sake's flavour is extremely important. It produces enzymes that break down rice starches into sugars, and proteins into amino acids. This process creates an array of flavour components, contributing to sake's unique umami, sweetness, and depth. A particularly interesting sake from our portfolio is our Kanadel Kijoshu, using a mixture of white and yellow koji, to create a refreshing acidity alongside the traditional sweetness of this style of dessert sake.
The type of koji, cultivation method, and style of growth all play a role in the final flavour profile, allowing brewers to craft a wide range of sake styles.
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Koji is not just a functional ingredient in sake brewing – it's a living, breathing part of the process which demands respect and expertise. Its role in creating the complex flavours we love in sake is unmatched, making it truly the unsung hero of the sake world.
