From the “sakana” series.
Close to Mediterranean bottarga, “karasumi” is a product traditionally made by salting a mullet roe and drying it in the sunlight. The taste is fine, complex, pronounced.
Modern technology gets is further. Certain amateurs age the karasumi vacuum packed, without any salt addition. This allows for an anaerobic fermentation process without putrefaction, a less salty flavour, a much longer aging period. Up to 6 years!
Colour darkens with time, taste gets deeper, aromatic length is marking. It becomes a refined, luxury product. The one on the picture was aged for 4 years.
It is a great companion for aged sake or even better, “yamahai” sake(*). Today though, the chef owner of RIN, my favourite restaurant in Shinjuku, was recommending a pairing with red wine. A rare recommendation for a product from the sea.
As soon as the pack is opened, taste will of course evolve, more rapidly, and take some slightly rancid notes.
(*) Yamahai: a sake produced from a particular form of yeast starter: a higher temperature on day one allows for several fermentations to take place in turn, until acidity rises to a level where alcoholic yeast only survives. It results in more complex flavours, with a “wild” or “gamey” character.