My last three batches of Miso - yellow, barley and chickpea - all had a somewhat unpleasant pungent bitter taste. My prior batch of 2 month sweet white miso did not have this. Yesterday I opened a 4 month black soya-barley miso, and it had this same flavor but very faint. I've been eating store bought miso for decades, and never once tasted this in a store bought miso. I make my own koji, and the only thing these batches had in common was the same apsergillus strain.
I don't really know how to describe this taste - it's not spoiled, it's not bad, it looked fine and to all appearances was edible, it just had this weird taste to it. I know it's hard to tell with actually tasting it yourself, but have any miso makers here ever had their miso batch turn out with a less than pleasant taste?