Steam it, slice it, dry it. Nothing is added at any point — no sugar, no preservative, nothing. That is the whole process, which is why households here still make their own rather than buying it.

The drying is done in the strong wind that comes off the sea. Shipping runs from November to the middle of March, so the season for making it is simply the season when that wind blows.

A white bloom appears on the surface. It is not mould. It is sugar — maltose — crystallising out as the moisture leaves. The raw potato does not contain it; the steaming breaks the starch down and produces it, and then the drying draws it slowly to the outside over a matter of days.

Production took off after two men who ran rice-cracker shops in Nakaminato — now part of Hitachinaka — began making and selling it as a product rather than as something a household dried for itself. This prefecture now accounts for the overwhelming share of the country's output, and most of that comes from three adjacent municipalities: Hitachinaka, Tokai and Naka. The method is about as simple as food processing gets, and the geography is about as narrow. Those two facts usually do not go together.