Koji is a mold that is at the heart of many different Japanese ferments. It is used to make miso, sake, amazake, rice vinegar, soy sauce, and mirin. Koji is grown on rice or barley, which are then used as the starter culture for further fermentation.
Making homemade koji is quite straightforward. The most difficult part of making homemade koji is finding the koji spores (koji-kin). You may be able to find koji-kin in your local Japanese grocery store or you can buy it online. Just make sure that it’s koji-kin, not koji rice.
Once you have koji spores in your freezer, making koji rice or barley is fairly simple.
Options for Koji Incubation
Koji needs to culture at 90 F (30C) for 48 hours. Here are a few options for keeping your koji kin warm enough.
- I have a Brød & Taylor Bread Proofer & Yogurt Maker, which I use for all my heated ferments. If you plan on doing a lot of fermenting, then I recommend making the investment. I use it for yogurt, cheese, tempeh, everything!
- A dehydrator or slow cooker set to 30C is also a great option.
- Alternatively, you can try to grow your koji in the warmest location possible in your house. Try in the oven with the light on, near a radiator or a hot water heater. The only trick is to measure the temperature as you go along because koji mold will start to heat up as it ferments. The right temperature is important because if it’s too cold your mold won’t grow, and if it’s too hot you will kill the spores.
How to Save Koji Mold Spores
If you’ve made koji rice or barley, then making koji-kin is easy. All you need to do is culture the koji mold until it spores.
- Allow the koji-kin to culture for more than 48 hours. You will know that the koji-kin has spored when your koji turns from white to greenish-grey. The green color is mold spores.
- Once the koji is green, remove the damp towel, and allow the koji rice to dry out in the incubator.
- After the rice has completely dried out, store it in the freezer.
- When using homemade koji kin to make koji rice, you only want to use the green powdered mold, not the rice. So sift the mold off of the rice with a fine mesh strainer before using it.
Homemade Koji Rice
Koji rice (and koji barley) is used to make miso, sake, amasake, rice vinegar, soy sauce, and mirin. Here’s how to use koji kin to make koji rice and koji barley. See the sections above for information on incubation options and how to save your own koji kin.
- Prep Time: 15 minutes
- Cook Time: 15 minutes
- Total Time: 30 minutes
- Yield: 4 cups 1x
- Method: Fermented
- Cuisine: Japanese
- Diet: Vegan
Ingredients
- 2 cups rice (white or polished brown)
- 1/4 tsp koji-kin culture (see notes)
Instructions
- Rinse the rice until the water runs clear (to remove all the starch).
- Soak the rice in water for 8-12 hours.
- Steam (not boil) the rice until it has softened. See notes below for my setup.
- Cool the rice to room temperature.
- Thoroughly mix the koji-kin culture into the rice.
- Spread the rice out in a baking dish. Cover with a damp tea towel (to keep it moist but not wet) and maintain it at 90 F (30 C) for 48 hours. See the section above for incubation options.
- Stir the rice every 12 hours to break up the clumps and evenly distribute moisture. After 48 hours, white mold fibers should have started to develop. Stop incubating at this point or the mold will spore.
- Store koji rice in the freezer until you are ready to use it to make miso, sake, or other koji ferments.
- See the section above for details on how to save koji-kin mold spores for future batches of koji rice.
Notes
- Since this is a mold ferment it’s important to keep everything clean and sanitized.
- For koji barley, use pearled barley instead of rice and follow the same procedure. Note: I haven’t personally tried this as I’m gluten-free.
- For steaming, I recommend using a vegetable steamer
or colander
lined with a tea towel. Just boil the tea towel to sanitize it before using it to steam your rice.
- Make sure you buy your koji kin from a reputable source. I recently heard from a reader who bought koji kin that was contaminated with a poisonous mold. It kept sporing with grey mold after just 24 hours. So if the recipe doesn’t seem to be working, it could be because the koji kin is contaminated.
or colander
lined with a tea towel. Just boil the tea towel to sanitize it before using it to steam your rice.Keywords: koji kin, koji barley, vegan, gluten free, sake, miso, soy free, nut free
Hi Emillie,
Thank you for your generosity in providing information and healthy recipes. I am interested in making Rice Koji and amazement. I have purchased a Brod and Taylor proofer and slow cooker all in one. I was just wondering if you have the same model do you use the proofer with water in the tray? Would be grateful if you could advise. Kind regards
Paul
Hi Paul, I do have that Brod and Taylor. Though I’ve never put water in the tray, I use the proofer to cook my koji rice… and pretty much every ferment! It’s good at keeping a reliable temperature.
Thanks so much for your prompt reply Emillie. I will follow your advice seeing you have had success with it. Was glad to hear you can do other ferments too
Hi Eillie,
Would be grateful if you could answer a couple more questions. The koji kin has arrived and just about ready to embark on my first ever rice koji. Re the baking tray- do you have to have a stainless steel tray or would a non stick tray be ok?
Regarding other ferments do you put the glass containers in the Brod and Taylor for your ferment?
There is a very quick recipe for Miso – it’s from the good british chef’s. They make it in 5 days. I have made it and it is quite light but tasty.
Kind regards
Paul
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Hi Paul. You could use a non-stick tray. I haven’t tried it, but it should work. I would put the containers for koji rice in the Brod and Taylor, but not miso. I usually leave miso in a cupboard to ferment (because I leave it for 6 months!) Interesting about a quick miso. I might try that next time.
Thanks again Emillie. Really appreciate your help.
Thanks again for your help Emillie. I thought you may have had to use a stainless steel tray. I have made miso using the 5 day recipe from Kuvings.
Thanks again Emillie. I thought you may have had to use a stainless steel tray. Yes, the quick miso recipe is an interesting one. It appears in a Japanese recipe using the Kuvings Yoghurt/ pickle maker. As I said it is light but I find it ok.
Keep up your good work.
Regards
Paul
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Thanks! I’ll look out for that.
can i make koji rice without koji spores
No… the risk of contamination is too great. Rice can contain Bacillus cereus which will cause food poisoning. You can buy koji online or at a Japanese grocery store.
Hello! I’m very much looking forward to making my first batch! If using a dehydrator, would we still want to cover the tray in a damp towel? If the dehydrator has a fan, should we turn off somehow? I’m a bit nervous about using it and wondering if it would be better to use the oven-light method instead. Thanks!
I have the same proofer. Though I’ve never added water to the little tray. I think that’s mostly for proofing instant yeast bread. I LOVE my proofer. Hope it works for you!
I already have rice populated with Koji that I’ve ordered from a Miso company I really like. Is there a way for me to propagate the same culture using the existing grain? My initial thought was to grind up a quarter cup or so into powder and use that as the starter.
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The koji rice will be too diluted for a good culture. You need to collect koji spores. So culture your rice, and allow it to continue fermenting until the mold spores (usually about 48 hours into the ferment). At that point you can collect the koji kin spores from the rice (or just grind up the rice).
I actually haven’t done this myself, but it should work. Cheers, Emillie
Emillie
I have a bag of dried koji rice. How should I culture it? Jus soak in water?
Usually koji rice is used to make other ferments. Try amazake: https://www.fermentingforfoodies.com/archives/1044
If you are wanting to make koji kin, continue fermenting for up to 48 hours, then skim off the sporing mold from the top of the rice.
Thank you Emillie for your advice. I just tried today by putting 1 portion of the dried koji rice, one portion of cooked rice and water enough to soak them and put in an air tight container. Now i just have to wait for 48 hrs to see some spore.
Did that sound right to you?
Are you able to maintain the heat? If not, then it might take longer to grow. Also, I wouldn’t have the container air-tight. Just keep a lid loosely on so that it keeps the moisture in. Let me know how it goes!
Hi Emillie,
I have had success with the Brod & Taylor proof box.
I place a 9″ pyrex pie plate on the bottom to serve as a reservoir for hot water. This can be periodically exchanged/refilled
The koji tray is supported above this by some cans of tomato paste at the periphery of the ”lower” level.
I was able to harvest about 500g.
I am not consistently successful in producing good steamed rice that is not clumpy. Is there a particular kind of rice that works best? Thanks
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Great! Glad it worked for you. Not sure how to make rice less clumpy. The rice needs to be sticky.
Thank you Emillie for this great recipe. Can koji rice be made with brown/ red rice?
I haven’t tried it, but I think it should work.
Hello
after only 24 H my rice get totally wet soaked ! , it tastes sweet and has a good smell , but is nothing like it should be /see from pictures the more i leave it the watery it get , what do i do wrong ?
bestsand thanks , stefano
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Hum, I don’t know, since I’ve never had that problem. The steamed rice should be quite sticky but not wet. And the only additional water is from the damp cloth. It should taste sweet. So maybe just leave it with a dry cloth, or stop there?
HI there, ever use the yogurt setting on an insta pot? I was thinking about trying that?
Thank you!
I don’t have an insta pot, but I’m sure it would work! The only reason why it might not be the best, is transferring the yogurt from the insta pot to containers for storage will probably cause a bit of separation (yogurt from whey).
I’m not sure how the insta pot works, but I have nested jars of yogurt with lids on in my slow cooker. Then poured water halfway up the jar, and kept them warm that way.
Heyo!
Im looking into growing my own spores from some locally made koji rice. You say to ‘culture your rice’. Could you explain what that means please?
This is the best resource I have found by far! Thank you so much for all your work. I can’t wait to try it out!
-Amanda
Thanks! Culturing means fermenting, or in this case allowing the mold to continue to grow. Does that make sense?
Hello Emillie
Can I use Saccharomyces cerevisiae (bread yeast) instead of Koji-kin (Aspergillus oryzae)? Unfortunately, there is no chance to find Koji-kin in my area.
Thank there
Sorry. Yeast is not the same as koji kin, which is a mold. Also trying to “catch” a mold culture is very risky. Which country are you in? You can often find koji online or in a Japanese specialty store.
Currently, live and work in Yerevan, Armenia and sadly there is no Japanese specialty store in the city.
So there is no chance to make Koji without koji-kin, is there?
by the way, thank you so much.
Sorry, not that I know of. It’s probably a long-shot, but are there any online local forums where you might be able to post a “wanted” ad?
I guess not. at least I don’t know, maybe there is. I’m a foreigner here in this country. After I have read your informative articles about fermentation, decided to try some of them in my free time. besides I love sake and can find plenty of excellent kinds of rice here to make it but…
Anyway, I enjoy your site and keep read your words…Thanks a lot for your kind replies
Thanks!
I was on another site and found that they will send it anywhere. i wasn’t really looking for that as I’m in Australia aand get it from an Australian site, but here is the link https://thejapanstore.jp/cart
Hi,
does it nesesary to steam rice,
can we skip that step?
And if we cant skip, whay we need to steam?
THank you.
The rice needs to be softened, but not too wet for the koji mold to culture well. I don’t think that soaking alone would soften the rice enough to culture.
So, in thery, I need to found way to soften rice or barley or corn etc. but not to be too much wet. Sounds posible 😀 Thank you.
Is the towel supposed to dry out? I am making koji now in a dehydrator, but I am worried that it wont work because the towel has dried out. Should I wet it?
I would re-wet the towel. The dehydrator does increase the risk of it drying out.
Thank youso much for being so prompt and thanks for your very imformative site.
My rice dried out. Do you think it is ruined, or should I try to keep it moist and keep going?
Actually, I think some rice i still moist, so I will keep going and ee what happens. It seems that I have to keep wetting the tea towel every couple of hours which i a real pain
Sorry to hear about the difficulties with keeping the towel wet. What if you used two towels? Also, depending on how warm it is, you could just turn off the dehydrator. If the mold has started to grow it will generate some of its own heat.
That is exactly what I am doing. I flicked a little water on it, mixed it in and put a second towel on and left it a couple of hours more. the towel had started to dry out, but had reached 41 degrees C so I broke up the clumps and left the heat off. It reached 40 degrees after about 5 hours – maybe sooner but I wasn’t able to check it earlier. It is starting to smell sweet and tastes sweet, but only about 1/4 of the grains have gone that stark white. I am pleased that it is working. it has now been going 50 hours but because of the way it looks I believe it needs longer. I will keep checking. I read that if you make Amazake with it and it works, you will know that it is OK. If I put it in the fridge then find it needs longer, do you know if I can keep going with the process?
By the way, I was thinking of buying the Brod and Taylor proofer and yoghurt maker to save further hassles. I clicked on the site and it was $169 US. As I’m in Australia I thought $240 Aus plus postage it might be worth it. But no, they wouldn’t let me order there because I am in Australia. If I go on the Australian Amazon site, it is $360 Aus. So unfair. I’m not going to get it. On some other sites it is even dearer. Not blaming you of course, just letting you know.
Sorry to hear that the Box is so expensive! It is rather large, so maybe that’s the issue with shipping? What a good idea to test your koji rice with amazake before trying a longer ferment. Besides amazake is delicious.
I think you should be able to continue culturing the rice after refrigerating. It will probably be a bit slow to start, but lots of my ferments pop in and out of the fridge.
Thanks, I’ll let you know how the amazake goes. I’ll make it tomorrow.
It is not the shipping; it is just that in Australia we get ripped off. Not sure why. It happens even for light weight products.
I think the amazake dried out. Not sure that it worked. May have to try again.
Hum, clearly a dehydrator isn’t a great option. Do you have a yogurt maker or slow cooker? You might be able to vent them to get the right temperature.
I bought some hulled barley as I thought it’s healthier than pearled.
Will the recipe work for hulled barley?
I’ve never used barley with a hull on it. I don’t know whether the hull is too thick and hard for the mold to grow through. I wouldn’t think so, I don’t think of barley hulls as particularly tough. If you try it can you let me know how it goes? Thanks! Emillie
Hi
I have a few questions, and please answer them.
1-Is koji rice the same thing as Malt rice? If isn’t: can you tell me what the malt rice is and how we can make it?
2-Does miso contain alcohol?
Hi Usama,
I had some server issues last week, and it unfortunately erased everything that happened during those few days! Including your previous comment and my response. Sorry about that.
Anyways, koji rice is not the same as malt rice. Malt rice is rice that has been malted (sprouted, dried and then toasted.) The malting increases the accessible sugars. Malt rice is usually used for brewing gluten free beer or making malted rice syrup, which is a sweetener. I recommend buying malt rice if you need it for a recipe. Either at a homebrewing shop or online.
Alcohol is generally made when yeast consumes sugar. Miso is a mold based ferment (koji kin is a mold culture) so I don’t think it contains alcohol.
Cheers, Emillie
I understand that they advocate making amazake to test the koji rice but then you’ve used it up so there isn’t any left to make miso with? If you grow the spores from the koji rice (as you have suggested in the comments) how do we know how much is enough to make miso (especially if we just grind up the rice with them)? Surely this should be a continuous process-something we can continually make once you have the initial mold, whether from koji rice or kojikin?
You can’t use amazake or miso to make koji rice, however, you can make larger batches of koji rice. Just make as much koji as you need to make miso, amazake, etc. Then leave some of the koji rice to spore for future batches of koji kin. You can even freeze koji rice for future fermentation, so making extra is always a good thing!
Hi! Thanks for your helpful instructions.
My rice dried out and I re-wet it a few times. It grew more koji, but now some parts are a little too mushy and slightly pink. Should I be worried about the pink color? The rice smells good and a little sweet and a little funky. But I’m worried about the slight pink color and mushiness. I’m going to take off the towel, let it dry out, and see what it looks like. I also don’t seem to be getting big chunky bricks or fully inundated grains like I see in pictures, but it does look similar to your picture. What do you think? Should I start over? Maybe try and make amazake instead of miso?
Pink isn’t a good colour. If just part of it is pink, remove that piece and try making amazake with the rest. I’ll admit growing mold is a bit tricky. Maybe try a container with less ventilation so you can control the moisture a bit better?
HI Emilie, I am currently at hour 56 and my rice has a yeasty and sweet smell but I don’t see the koji coating growth or dry clumps like I would see in Google images or youtube tutorials. My rice is white translucent in color (like normal rice color with clumps of white powder from rice flour I used to distribute the koji with), damp and the grains are independent of each other ( rolling easily if I tilt my tray and I do see a growth but most of them are at the bottom of the rice on the tray (while in most pictures and tutorials I see it on top of the rice). Is this normal? How do I know the koji rice is ready to use or if I need to start over?
It sounds fine. I think the added rice flour might make it harder to see the mold. If you’re concerned, try making a quick koji ferment (like amazake: https://www.fermentingforfoodies.com/homemade-amazake/ ) to test the rice before making miso or sake. I wouldn’t let it go too long because you don’t want it to spore. Good luck!
My name is Bob and I’m an instant fan. Thankyou for not sharing detailed, torturous journeys to the recipes. .
Hello. I purchased some koji-kin. I would like to make Mirin. Do you have advise for making Mirin? I’m not able to find shochu in my area. I’ve located sake and soju. I am not sure that either of these would be a suitable substitute for shochu.
Thanks,
Yolanda
Hi, I haven’t made mirin. However, you might be able to use sake instead of shochu. I’ve got a batch of koji rice right now… maybe I’ll join you in attempting something new. Good luck!
Hi Emillie!
I really appreciate this post, I’m a fan of Koji but I have never seen directions for how to grow your own koji-kin before. I have a question for you. I would like to maintain my own koji culture so that I don’t need to buy koji rice or koji kin every time I want to make a ferment. Is it better to culture extra koji rice and dry that, or is it better to grow extra koji rice, let it sporulate, then save only the spores to start the next batch? It seems easier to just dry the cultured rice, but that doesn’t explain why people use Koji-kin a lot. Thank you!
Kevin
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I’ve only just cultured rice. However, you could certainly let the mold spore and collect more koji-kin for future batches of koji rice. Personally, I find that sporing mold bothers my allergies. 🙂
Hi Emillie,
I have tried your recipe to make rice koji and twice ended up with gray matters growing while keeping warm for 48 hours.
I thought that I did not sanitize the tools enough.
So this time I sanitized every thing very carefully.
But at 24 hours, ai saw again spots of gray on the rice.
I carefully took them away, but am afraid that I am still doing something wrong.
Could you instruct? I am a bit lost.
Thank you.
Yuki
The grey sounds like the koji is sporing. Though that should be more of a green-grey than pure grey. Either way, it sounds like you have very active koji kin! Try stopping after 18-20 hours and test your koji rice on something quick like amazake. If it works, then you’re fine to use it for miso and sake. Good luck!
Hello Emillie. Thanks for sharing your expertise! I eat a lot of fermented foods, including miso, amazake, tempeh, etc., and would like to have a go at making koji rice from koji-yin to make red miso once (to see if I can do it – allowing it to ferment for a year), and white miso more regularly, perhaps once every month or two. I will highly likely try making amazake also, but as I am just one person I might not need to be fermenting very regularly. I don’t have a freezer as I don’t eat frozen foods, so my question is how can I store any koji-yin that I make after it has spored? Is it possible to sift off the spores after the rice has dried out, and then keep the spores in an airtight container instead?
Thank you in advance!
Glad to meet a fellow fermenter! Yes, you can store cultures as a dried out powder, however, I still recommend keeping them in the fridge or freezer. Cultures just last longer that way. If that’s not possible, then just make sure you regularly use and make culture. I can’t say exactly how long a culture is shelf-stable without refrigeration… but probably a few months at least. Enjoy!
Nice and easily understandable recipe. I did koji rice for sake some years ago, and that was a job and a half. But sake was nice.
This time it will be for baking sourdough bread, so there will be a batch of wheat, rye and barley and maybe oats going into the proofer to see which one will make the best bread.
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How interesting! You’re going to use koji for bread? I’ve never heard of that and would love to know what you’re doing. Thanks for sharing!
Hi Emillie,
Love your site, I have made Koji rice twice now and am about to start on my second batch of miso.
For all your readers who are interested, I made up a device for incubating the rice at the specific temperature.
I used a polystyrene box with lid, a heat mat ( for starting seedlings on – thus waterproof), cake racks and glass jars as shelves and supports. With a variable voltage plug adaptor to adjust the temperature and a hole in the lid with a thermometer to monitor temperature. The first time I used a box with a light globe (small ie for a fridge) and the plug adaptor (variable rheostat basically).
Both times very successful.
Should be able to pick up that sort of plug from an electrical store, the rest is pretty easy to come by and the cost is minimal.
I used pyrex baking dishes for the rice, which I soaked overnight and steamed in a wok and bamboo steamer setup.
I like your idea of collecting the spores and will explore that in the future. I still have plenty that i bought a while back.
Should I keep it in the freezer? I see you mentioned that, it’s been in a jar on the shelf for over a year and is no less effective.
I also do a bunch of other ferments, yoghurt, always have made sourdough for years, just started on a Nukazuke (ricebran pickle) tub.
Hi Jim,
Thanks for sharing your DIY incubator. It sounds perfect for all sorts of ferments!
Definitely store both your koji rice and your koji kin in the freezer. I think that comment about letting it sit in a jar on the shelf for over a year was referring to miso not koji. Miso will last forever… and I’ve never had any problems with it. Enjoy!
Hi-I just bought a Brod and Taylor on your recommendation, managed to successfully make some koji barley, and am now making shio koji from it, so thanks! I’m looking forward to doing more. In the meantime, I have a question that may not be within your purview, but…there are a couple companies that are using what they call “koji protein” as a meat substitute. They claim that they culture the koji fungus filaments to the point where they become large fibrous masses that can then be cut, treated, and sold as “meat.” Since koji is a microorganism and the fibers I have seen are very small, it seems unlikely they could be grown to such a size—and then used as mass-produced protein. Does this make sense to you?
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The only way it makes sense to me is if they’re using the koji to bind together something else… beans, nuts, grain. However, there is a host of mushroom proteins coming on the market, so maybe they’re feeding it some sort of nutrient substrate to get it to grow into a mass? I don’t really know how they work, but it’s an up-and-coming thing! Cheers, Emillie
Hello i need your help can i use tempeh starter instead of koji starter to make koji rice
Thank you ☺️
Hi Rasha, While tempeh and koji are both molds, you can’t just swap them. Koji is quite different. If you don’t have koji kin, maybe you can find koji rice? If you have a really good Japanese grocer they should stock it in the freezer.
Good luck!
Small point: While your instructions will probably work with long-grain rice or basmati rice, I would suggest that beginners first learn with short-grain rice, which is usually starchier than those other varieties. Ideally it would be a Japanese variety, but I’d expect that European or American short-grain rice would have similar results to Japanese rice.
If you use repeat the process over multiple generations (using the same kind of rice each time and the spores from the previous batch), the koji should adapt to the characteristics of whatever rice you’re using. Natural selection.
Thanks for sharing!
Thank you for the post on your blog. Do you provide an RSS feed?
I do have an RSS feed. But my sharing app doesn’t have it as an option. However, you should be able to subscribe through your viewer. Cheers!
Definitely, what a great site and revealing posts, I will bookmark your site.All the Best!
Thanks!
some genuinely interesting information, well written and broadly user friendly .