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May 15th, 2011 at 5:53 pm

Aroma during koji production

Today as I am making a test batch of koji that I am working on as a new offering (Special Ginjo Koji-kin), I am led to thinking about the aroma of the growing koji. What is that smell? Where does it come from? Well it seems that the answer, at least at the level I can discuss here, is not that complicated.

The aroma of a fresh batch of koji is often described as being chestnut like. This aroma was noticeable during my check of the growing koji at 20 hours into the process, not strong but definitely there. As the time goes by the aroma is strengthening. I am not sure if I would equate the smell of koji with chestnuts but I find the smell nice and even comforting. So what is making this aroma?

It seems that the aroma is coming from a combination of phenylacetaldehyde, 1-octen-3-ol and 1-octen-3-one. Production of phenylacetaldehyde seems to stop at around 40 hours into the process while the production of 1-octen-3-ol and 1-octen-3-one continue and can even double their concentration during the final stages of koji production (hours 44-50). However, as 1-octen-3-ol and 1-octen-3-one concentrations overwhelm those of phenylacetaldehyde a more mushroom like aroma becomes noticeable. Individually phenylacetaldehyde and 1-octen-3-one have a rose like and a mushroom like aroma respectively.

As mycelia grow they produce linoleic acid. From linoleic acid 1-octen-3-ol is created and 1-octen-3-one is an enzymatic oxidation of 1-octen-3-ol. So the more mycelia growth there is the more 1-octen-3-ol and 1-octen-3-one there will be. One study found 5 novel compounds that are important to koji aroma:

Compound Aroma
1-octen-3-one Mushroom-like
2-methyl-2-hepten-6-one Nut-like
methional Potato-like
phenylacetaldehyde Rose-like
(Z)-1, 5-octadien-3-one Geranium-like


Finally, one study showed that they could reproduce the aroma of koji by blending 2-methyl-2-hepten-6-one, methional, 1-octen-3-one, 1-octen-3-ol, and phenylacetaldehyde. This indicates that while phenylacetaldehyde, 1-octen-3-ol and 1-octen-3-one are the primary components of the koji aroma, a little more is needed for the full effect.

And there you have it. Anyone want a koji aroma perfume?


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  • Claes Nilsson
    2:51 am on July 11th, 2011 1

    What studies are you referring to? I would like to read more about it 🙂

  • Will
    11:02 pm on July 11th, 2011 2


    The studies I am referring to are mostly from google searches for “koji aroma” and the like. I have not recorded them. I am traveling so I don’t have the access needed at present to give you a better answer. I’ll try to do so later.

  • Will
    10:06 pm on July 24th, 2011 3


    Three of the studies I was referring to are:

    GC-Olfactometry analysis of the aroma components in sake koji. by TAKAHASHI MIE et. al., in the Journal of the Brewing Society of Japan
    Change in the aroma of sake koji during koji-making by Takahashi et. al, in Journal of the Brewing Society of Japan (May 2007)
    Analysis of Volatile Compounds in Shochu Koji, Sake Koji, and Steamed Rice by Gas Chromatography-Mass Spectrometry by Yumiko Yoshizaki et. al., J. Inst. Brew. 116(1), 49–55, 2010

    Hope this helps,


  • sasi
    10:45 pm on December 15th, 2012 4

    Hi, your writing about koji is interesting, do you have any other idea about shochu, koji, or anything related,for my research proposal:).thx

  • Will
    12:21 pm on December 17th, 2012 5

    Sasi, You will need to say more about your research proposal for me to answer this.

  • Josh
    7:14 pm on February 16th, 2015 6

    Hello, my first batch ever of koji is smelling like urine. I had heard about the wonderful aromas of koji, but I am not finding this wonderful. It’s been over 24 hours since starting it and most of the rice grains are coated with the white powder now. Is a urine aroma a sign of a koji ferment gone bad? Or will the smell change in the next 24 hours? Thanks!

  • Will
    7:53 am on February 17th, 2015 7

    Josh, I have never heard of a smell like this but perceived aromas, like tastes, have a high degree of individual sensitivity. That is, we don’t all smell the same things just like we don’t all taste the same things.

    Anyway, I don’t know if the aroma will change but it sounds like the koji is progressing just fine. You can taste a kernel and it should be just a little sweet.




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