A white sweet, made from four things: yam, rice flour, sugar and water. Steamed for twenty minutes or more, the batter sets into something springy and half-sponge, and a cut surface shows a fine even scatter of holes.

The yam matters. The long, watery kind will not do it; the wild mountain yam is what works. So a bad year for yams pushes the price up, and in the worst years the sweet becomes difficult to make at all. A confection whose cost is set by what the hillsides did that season is not a common thing.

It appears to have been created in Satsuma somewhere between the 1680s and the 1710s, and the reason is unusually clear. Wild yam grew by itself on the volcanic ash plateau that covers this region, and sugar from the Ryukyus and the Amami islands could be had more easily here than almost anywhere else in the country. Both of the difficult ingredients happened to be close by.

Most of what is sold now is the filled version, karukan-manju — a ball of the same batter steamed around sweet bean paste, which has become the more usual form. The plain white kind, with nothing inside it at all, takes a little more looking for, and it is the one that tells you what the yam is doing.