No vinegar goes into it. Sake goes in instead — not cooking sake but the local lye-treated rice wine of Kagoshima, poured over until the rice is soaked through with it.

Rice and ingredients are layered into a wooden tub, the sake is poured across each layer, and a weight goes on top, adjusted by hand as it settles. Four or five hours later it is ready. In that time the enzymes in the sake ferment the rice and the filling very slightly and pull sweetness and depth out of both of them. When the lid comes off, the smell arrives before anything else does.

The practice is said to go back to the Edo period, and the tub and the weight have not been improved upon since. Prawn, sea bream, ark shell, octopus, butterbur, bamboo shoot, shiitake, shredded omelette, fried fish cake. The rule is that anything which suits sushi may go in, which is not really much of a rule.

The origin story concerns a mistake. After a cherry blossom party given by the lord of Satsuma, a servant is said to have put the leftover food and the leftover sake into a tub together and gone to bed. The next morning the tub smelled wonderful. A failure to clear up became a dish, and people have been recreating the accident deliberately ever since.