we want to make miso and we have some koji ready. It's not that much though and we are wondering if using a 5L jar for about 1.5kg of miso might be a problem. Are there issues with air circulation or surface exposed to the air?

Thank you

1 Answer 1


I have been into miso for a short time, so I am far from being an expert and I won't attempt a complete answer. However, let me raise two points which I think are relevant:

  1. It is common to remove and dispose the thin dark layer that was in contact with the air when harvesting the miso. The reason is that LAB bacteria present in the air often proliferate on that layer, yielding a rancid and acid layer of miso which you are not looking for. A larger pot will likely have a bigger surface cross section which will yield a bigger layer in contact with the air. In other words: putting little miso in a large pot will yield you less finished product. In my opinion it is a pity to think you will be throwing away a good proportion of something you waited months to make!

  2. According to the Noma Guide to Fermentation, you should put a weight of about 50% the total mass of the miso during the fermentation process. I believe that what is really relevant here is not the mass on the top of the 'miso cake' but rather the pressure exerted on cake. If that is correct, using a big pot for a small cake will probably require you to put more than 50% of the cake weight in order to get the same pressure 50% mass would exert in a smaller pot (and in the extreme case to distribute it well accross the surface).

Maybe you have already crossed these videos, but if you have not I recommend watching this, this and its follow up to see the recipients and weights they use.

  • 1
    thank you for your answer. The pot I plan to use is somehow vertical so there's not much difference in the cross section. For sure a low, wide pot would be a bigger problem.
    – Chobeat
    Jan 11, 2019 at 17:36
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    @Chobeat, if the only thing that changes in using this 'tall pot' is the height and not the radius of the cross-section, I think really there is no difference to a smaller pot. Just make sure to properly sterelize the jar walls before putting the miso and cover the air-miso interface with cling film. Jan 14, 2019 at 9:29

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