Koji is a type of Japanese fermentation starter – a grain (usually rice) that has been inoculated with a type of mould called Aspergillus Oryzae. While yeast is the magical key to many western food favourites – bread and beer being just two examples – koji serves a similarly vital role in Japanese cuisine, kicking off fermentation in sake, soy sauce, miso and mirin, to name a few.
The wording around koji can be a little confusing at first, as it refers both to the specific mould and to the grain that has been inoculated with the mould. Although rice is the most common grain used to make koji, other grains like barley can be used, or even legumes like soy beans. Nuts and seeds can also be used to make koji, if you’re feeling particularly experimental!
To make koji, partially steamed rice is inoculated with koji grains or spores and left to ferment in a warm, humid atmosphere for 5–7 days, where the mould feeds on the rice and breaks it down until the carbohydrates transform into sugars and produce glutamate (also known as that magical ‘fifth flavour’, umami). This can then be used as a ‘starter’ to make many fermented products such as sake, miso, soy sauce or a seasoning paste known as shio koji.
The recipe below comes from Dean Parker, head chef at The Manor restaurant in Clapham. Use this to try making your own miso paste, including Dean's cacao nib miso or toasted sesame miso. You can also use koji in porridge, blend it into smoothies or add it to rice pudding – the possibilities are endless.
For this recipe you'll need a fair amount of kit, including:
1 x spice grinder, powerful blender or food processor to grind the koji rice
1 x shallow perforated gastro tray with well-fitting lid
1 x deeper gastro tray for the perforated gastro tray to sit in
Large pieces of muslin cloth
A steam oven or rice cooker
Lengths of elastic or string
Cling film
A temperature-controlled environment, such as a dehydrator
Sterilised utensils
You can use your koji to make homemade miso. While miso is traditionally made by mixing koji with soy beans, you can have fun experimenting with any bean, nut, seed or legume. Dean Parker’s recipes for cacao or toasted sesame miso are delicious used in sweet or savoury dishes.
Another popular and easy use for koji is koji salt or shio koji, a sweet, mild miso-flavoured paste often used as a marinade, pickling solution or low-salt, umami rich flavouring for stews and soups, such as Rosana McPhee's Japanese cream stew recipe.
