Summary of koji
Shio koji (塩麹) - Rice malt fermented with salt
Shouyu koji (醤油麹) - Rice malt fermented with soy sauce
Shouyu (soy sauce) koji and shio (salt) koji are traditional Japanese condiments/seasonings that can be used in a variety of ways to increase flavour and umami in food. They are so flavoursome that you can just top it on rice to eat! It doesn’t get more Japanese than that. You can also use it to marinate meat or add to dishes during cooking. You can also just add a dob of it on the side in your next bento box as a dipping sauce.
Koji is usually made by fermenting a starter culture of cooked grain (e.g. rice malt) that has been mixed with a fungus called Aspergillus oryzae. This fungus is commonly used to produce Japanese sake, miso and soy sauce.
In Japan, you can easily buy ready-to-use koji in supermarkets. In Australia, pre-made fermented koji is pretty popular too and can be found in Asian and speciality stores and online, but choices can be limited or it’s expensive. The taste could also be too sweet due to mass production. Luckily, you also can easily make a fermented koji culture at home to your taste, and to use in any way you like. And you can store them in the fridge to use for months once fermented.
In this quick food brief, we describe how to make two types of koji – a soy sauce based one and a salt based one. You will need to purchase a rice malt koji starter culture for this though. We recommend going to https://www.enokidomiso.com.au in Sydney. Or just browse online with the keyword “koji starter kit”.
Recipe guide to preparing shio and shouyu koji
1. Find a jar (we like glass as it is easy to see through), clean and dry thoroughly.
2a. For shouyu koji, add 200g of the koji starter to about 400ml of soy sauce (adjust the volumes as needed, but keep a 1:2 koji to soy sauce ratio).
2b. For shio koji, use a ratio of 230ml water, 200g koji starter, 60g salt. Often there is a recipe that comes with the starter kit, so just follow that for starters. You’ll find recipes will vary wildly when you search online, so it’s best to use this ratio as a guideline and adjust as your taste suits. Just make sure that the koji is well covered with the water.
3. Leave at room temperature to ferment. Do not close the lid to air tight. Just tight enough to let any air out during the fermentation. In summer it may take up to 1 week before it’s ready, and in winter it may take 2 weeks.
This is how it should look like at day 1.
4. You will need to stir through with a clean spoon daily to check the consistency and colour, and to make sure the fermentation is happening uniformly throughout the mixture.
5a. For shouyu koji, once the rice grains are very soft and the consistency becomes gooey, it is done (again it should take about 1 – 2 weeks). If you find the rice grains have absorbed the soy sauce in the first day or two, you can top it up with soy sauce again to about the same volume. The final culture should have the rice malt lose its white colour.
5b. For shio koji, once the grains are soft and there is a sweetish smell, the fermentation is done. This will take up to 1 week in summer, up to 2 weeks in winter. Like the shouyu koji, if water is absorbed in the first day or two, add more water to top up to the initial volume.
5c. Remember to mix the cultures daily!
Day 4 of fermentation. You can still see the grains.
6. If the fermentation goes for too long, alcohol will start to be produced. This will be pretty obvious, and you’ll need to start over. You can do a taste test daily.
7. Once done, you can store in the fridge for 3 – 6 months! How great is that?!
Day 7 - after stirring, the grains appear disintegrated and much smaller.
A closer look at shio koji:
A closer look at shouyu koji:
Using shio koji to make a yummy steak don bento
Ok, so now you have your koji. What do you do?
Using it on a steak is a pretty darn no brainer as it tenderizes the meat and brings out umami. Here are a couple of pictures to get your tastebuds excited. We marinate the steak with shio koji for 30 mins to 1 hour at room temperature, and then cook to liking.
Slice the meat and put on rice with some veggies, and you’ll have a delicious steak don (steak on rice) bento! These were prepared in the Cherry woodgrain 1 tier bento box and Matte White Nuri Wappa 1 tier bento box.
View the making of this bento on YouTube.
Are you ready to prepare some koji?
Well, there you have it. Apart from purchasing the rice malt koji starter, making your own shio or shouyu koji is as really easy. There are TONS of recipes on the web, so you can do some searching first to find one that you feel works best for you. Either way, you’ll have a super seasoning condiment now to prepare mains and side dishes not just for your next bento, but for any meal at home.
