Frequently asked questions about Koji

What is Koji?

Koji is the term for a grain or bean that has been inoculated with Aspergillus Oryzae, a special fungus that has been domesticated for about 9000 years. 
White Rice Koji is made by steaming white rice and then allowing spores of Aspergillus Oryzae to germinate and multiply on it. 
This process is carefully controlled to ensure conditions are perfect for koji growth, with both temperature and humidity monitored continually. The fungus then converts starch within the rice into a range of enzymes, which go on to create the delicious range of savoury/umami flavours within foods like miso and soy sauce.

Can you eat Koji?

Koji can be eaten raw, but is at it’s best when added to other ingredients to create an umami flavour in the food.

Does Koji contain any allergens?

Koji does not contain any of the 14 allergens named by the UK food standards agency, and can be used to make allergen free alternatives of popular Japanese foods such as miso (e.g. using fava beans or green lentils), or soya sauce (using fava beans)

Is Koji vegan?

Yes, Koji just contains rice and a fungus and is completely vegan.

If you have any more questions about Koji, or how it is used, please leave a question in the comments and we’ll do our best to answer it.  

17 thoughts on “Frequently asked questions about Koji

  1. Hi,
    Do you make koji yourself, in the UK? Or is it imported?
    Thanks

    1. We make all our koji here in the UK – in rural Worcestershire. It’s all handmade in small batches.

  2. Hi, how long is the shelf life? Where should I keep it before opened and after?

    Many thanks.

    1. The shelf life is four months from manufacture, so will generally be 3+ months from purchase.

      Before opening it can be stored on a shelf/in a cupboard – just as you’d store uncooked rice.

      After opening it is very important that it stays dry. I have stored open koji for many several months here, but there is a danger it will go bad if exposed to moisture. If possible, store in an airtight container.

  3. Hi. I wonder if you sell just the fungus (Aspergillus Oryzae)? If so, what’s the price per, say, 15g?
    Thank you.

    1. Sorry, due to the agreement we have with the Japanese spore producer we are unable to sell spores – only koji rice.

  4. Hi,
    If im making koji water (blending koji and water and sieve it well) is there an easy (or multiply) way to stabelize it? so it would hold in a fridge longer than 5 days?

    1. It will probably be OK in a fridge for a lot longer than 5 days, but I have to remain on the cautious side of things. The easiest way to get it to last longer is to increase the salt content – or you could add some neutral alcohol. You can also freeze it, or even dehydrate it.

    2. Hi! Keen to try, but I’m interested To know what prevents the growth of Bacillus Cereus when producing the rice koji? Steamed rice at room temperature would normally give optimum conditions for that to grow?

      1. Yes, Bacillus Cereus is something that koji growers have to be aware of. The rice is steamed, which kills any Bacillus Cereus present. The steamed rice is then cooled quickly, giving any remaining spores as little time as possible to germinate. The steamed rice also has a very different texture to cooked rice – it is drier (has a much lower aw) which means conditions aren’t favourable for the B cereus. All the conditions are stacked in favour of the koji, which means the B Cereus doesn’t have a chance. Our koji is also lab tested at regular intervals to check our processes, ensuring B cereus isn’t an issue.

  5. If I have a rice allergy or mold allergy should I consume rice koji or koji of any kind?
    I do take aspergillus in a digestive tablet with no reaction.

    1. If you have a rice allergy you should not eat rice koji or anything made with rice koji.
      I’m afraid I can’t advise on the mold allergy – that depends on the type of allergy you have. There are thousands of different fungi and without testing I couldn’t say whether it would be safe. If you have eaten aspergillus oryzae in the past then it may be fine. But do not eat if you have a rice allergy.

  6. Hi …… Do I get the same nutrition value if consuming Koji Spore in raw form without and cooking or marination involved.
    Is it safe to consume Koji Spore in raw form?

    Thanks

    1. The nutritional power of koji is obtained by using it to ferment other things. The koji creates a range of nutrients, including all the essential amino acids that the body needs, when used to make things like miso or amazake. If you’re after as much benefit as possible from the koji then do not cook the miso after making it – eat it raw.

      Rice koji is safe to eat raw, but it would be like eating raw rice, so I wouldn’t recommend it.

  7. Hi there, I was wondering if rice koji is safe to eat raw, would it apply to all koji products like barley koji, soybean koji? Given that it would go through the same process: soaked -> steamed -> inoculated -> maintenance. I am attempting to use barley koji as an outer shell/component for a dessert.

    1. Yes, fresh barley koji is safe to eat raw.

      1. Thank you!

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