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Koji-kin fail due to light exposure?

Hi all, new to the forum. I’ve read almost all the posts here that I can follow since I don’t know much about this yet.

I ordered the vision koji-kin powder, and decided my first endeavour would be to get myself a good supply of koji-kin so that I wouldn’t have to keep reordering it.
I decided on using an old mini-fridge as my incubator, and a dual 50w grow light setup as my heat source. The koji grew very slowly, at less than half the rate Taylor describes in his guide. It did stay white, but did not seem to penetrate as well as his guide describes. After the initial koji growth, I removed the moisture source as directed. The first batch dried up to the point of being crunchy, which was my suspect for it failing to continue the process. The second batch did not get crunchy, however also failed to continue the process where it should begin to turn yellow and then continue on to green. Only very isolated small clumps of rice appeared to somewhat continue the process, but after letting it go for a couple extra days seemed to turn into the wrong type of mold…
First batch discarded… second batch waiting at home… I may take pictures to see what you guys think.
I have two ideas about this… first being that the koji is light sensitive, and the growth could have been retarded by the exposure to the harmful light waves emitted by the bulbs… second being… maybe my koji-kin powder got hot in the mail and the heat damaged the spores somehow also hindering normal growth.

I understand this is a lot from a newcomer, but I would greatly appreciate any help you guys could give.

I also used some of this apparently sub-par koji in a moto… which looks more like oatmeal and does not seem to be liquifying like most of the pictures that I have seen online.

I can’t find any source that says anything about koji being light sensitive one way or the other. Honestly, the omission of any information regarding the incubation temperature makes me think that there is a variable that maybe needs to be monitored more closely.

Incubation temperature for both attempts was set at 35.5C with a 0.6C band. I don’t have a method of humidity control yet, but I just ordered a controller that looks very similar to the stc-1000 I already have for temperature.
I have continued reading more posts on making tane-koji (think thats what it’s called) and apparently I also need a source of fresh oxygen as well?? How is this accomplished using an ice chest as the enclosure?

I’ve been working 12 hour shifts for the past month, but I had been checking it a few times between getting home and going to bed, then another couple times in the morning before leaving. The highest temperature I saw was 37.7C, which shouldn’t have prevented the koji from replicating.

I think it’s safe to say at this point, that the koji I have made is sub-par. I added the yeast to the moto two days ago and it just now started making bubbles… the rice still does not appear to be noticably liquifiying.

Wait…you’re not aerating your koji? No wonder it’s dying on you! Aspergillus oryzae is highly aerobic, man. That’s the one of the reasons why you have to take the koji out every few hours and give it a stir. If you’re keeping it sealed up with no access to oxygen, you’re suffocating the mold to death.

I feel ya on the 12 hour shifts, man. I’ve worked on the Alaska north slope. :slight_smile: If you can’t be available to stir the koji once in a while, then you need to come up with a way to ventilate your incubator. How are you going to do that with a cooler? I don’t really know. I only suggest using a cooler because they’re cheap, portable, commonly available, well insulated, and don’t need any assembly. The caveat is you have to be available to babysit your koji for 40 to 50 hours.

Edit: if you’re just trying to make tane-koji to inoculate future batches of kome-koji (to make sake with), you don’t need an incubator. It will take more like a week, and the result is unsuitable for brewing sake due to low enzyme production, but you really only need room temperature to successfully make tane-koji.

Oh wow… I have to laugh at myself a bit on this one… I completely misunderstood the “highly aerobic” part. If I can make tane-koji at room temperature, it sounds like I don’t need the enclosure at all after the initial 24 hours. No wonder the mold wasn’t growing correctly!
Looks like I’ll have to wait for more koji-kin to come in the mail before I can take another swing at it.

On a different note, I’ve heard of different kinds of koji-kin… some supposedly of higher quality than others… where do you get the better koji-kin?

I don’t have a good answer for that one, sorry.

Thanks a ton for the help. I can’t beleive something that should have been common sense escaped me so easily!..almost everything that grows needs oxygen. That must have been why my koji didn’t get fuzzy like your picures show… it was just starving.

You mentioned only room temperature is needed for tane-koji… is this after the koji process is complete, or after initial inoculation?

I plan to write an entire article on making tane-koji in the near future (when work and family life permit me time to do so), but here’s the basic outline:


  • Koji grows just fine at ambient room temperatures, just slower.[/*]
  • At this lower temperature, the mold doesn't produce the high quantities of enzymes that brewers are after. [/*]
  • Potassium promotes mycelial growth. Hardwood ash (2% dry weight) is the traditional source of potassium used in production of tane-koji.[/*]
  • Brown rice is also traditionally used, but that stuff is very time and energy intensive to steam. Plain white rice is less of a PITA to deal with.[/*]
  • I’ve ran across several web articles mentioning using additives to their substrate to promote the tane-koji production. How is this measured and applied to our process? (off hand I would guess it is simply mixed into the rice)

    I just odered a 50g packet from vision… well “just” meaning two weeks ago… so if you need any help experimenting let me know, I don’t know a lot, but I’m willing to try and help… and I’ve learned a lot every time I’ve failed so far!

    Hi Bob,

    Your previous articles has been a major influence to me liking sake brewing, and I will look forward to reading your article on tane-koji. I have never got around to reading that much about koji as I would have liked, so this is a most welcome initiative. The entire transformation part from kome-koji to tane-koji is particularly interesting, and I hope that you will cover this part.

    This is not really correct. A lot of fungi and bacteria are facultative anaerobes, meaning that they do not require oxygen for growth. There also exist fungi and bacteria that are obligate anaerobes, meaning that they only grow when no oxygen is present.

    For most parts during sake fermentation, yeast grows, whilst fermenting sugars into alcohol, in anaerobic conditions.

    • Claes
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