In autumn the riverbeds of Yamagata fill with pots. Groups arrive with firewood and folding tables, build a fire on the stones, and boil taro until it gives under a chopstick. In Yamagata this has a name of its own, imonikai, and it occupies the weekends of October the way a sport might.

Inland, around Murayama and Mogami, the pot is beef and soy sauce. Cross the mountains to Shonai and it becomes pork and miso. The prefecture is divided on this, cheerfully and permanently, and the argument is part of the pleasure. In the Okitama basin they add tofu and daikon and consider the matter settled.

The origin usually given is river trade: boatmen on the Mogami River boiling taro and dried cod from their own cargo. The riverbank gatherings themselves are more recent than that, becoming a fixed custom only around the eighteen-nineties, which is not long at all.

At the largest events the pot is over three metres across, a crane lifts the ladle, and several thousand servings come out of a single fire. The real thing, though, is the small pot: eight people, a windbreak of cardboard, and someone's uncle insisting on the correct order of ingredients while the others pretend to listen.