Mackerel is salted and left for ten days or a fortnight. Then it goes into rice bran and stays there for something like ten months. The liquid the salting draws out of the fish is often put back in as seasoning, and soy sauce, mirin, shochu or sake lees may go in with it, depending on the household. It was made to get a household through a winter, and the timing was set by that and by nothing else.

What comes out is brown and coated in bran. You brush most of it off and hold the fish briefly over a flame. It is very salty, so a small piece goes on top of rice, or into tea poured over rice, or beside a drink. One slice will finish a bowl of rice on its own.

Several explanations exist for the name. One says it comes from an old verb for pressing fish down into a barrel. One says it is a worn-down form of an old word for a salted paste. There is even a suggestion that it came from Ainu.

Salt, bran, and time. Nothing else goes into it, and it takes ten months. A preservation method built for a season that no longer threatens anybody is still being carried out at the same speed, and a well-aged one can apparently be eaten raw, without the flame at all.