Not a single grain of salt goes into it. The leaves of red turnips are chopped, dipped briefly in hot water, and mixed with a starter kept from the previous year's batch. Lactic bacteria do the rest. It is kept warm at first and then left in the cold for about a month, and what comes out is sour rather than salty, with a smell closer to yoghurt than to anything in a pickle jar.

Kiso is deep in the mountains and a long way from any sea. Salt had to be bought and then carried in over passes, which made it the most expensive thing in the house. There was a saying here: lend your rice if you must, but never lend salt. The pickle exists because the ingredient everyone else relied on was the one thing this valley could not spare.

Nobody can date it exactly. It appears in a linked verse by Basho's circle, and in a document from about a hundred and fifty years ago, which puts it at three centuries at the very least and probably more.

Because the starter is carried forward, every household's sunki tastes slightly different from its neighbour's. Last year's barrel seeds this year's, and has done so for as long as anyone can account for. That continuity, rather than any written recipe, is what the thing actually is.