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:
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?