Every autumn, something odd happens on the riverbanks around Yamagata City: families, coworkers, and whole neighborhood associations haul pots, propane burners, and sacks of taro down to the water’s edge and spend the afternoon cooking and eating together outdoors. The dish is imoni — a soy-simmered taro and beef hot pot — and the custom of cooking it riverside, called imoni-kai, is one of Tohoku’s most distinctive and least internationally known food traditions. If you’re in northern Japan between September and October, it’s worth planning around.
What Is Imoni, Exactly?
Imoni (芋煮) literally means “simmered potato,” though the main ingredient is satoimo (taro), not potato. In Yamagata’s standard Murayama-region version, peeled taro is simmered in a dashi-and-soy-sauce broth with thin-sliced beef, konnyaku (konjac), and long green onion until the taro turns creamy and slightly sticky — that starchy thickening is actually the point, and locals judge a good pot partly by how velvety the broth gets. Across the mountains in the Shonai region near the coast, the same dish is often made with pork and a miso base instead, so you’ll hear Yamagata people debate “beef-and-soy” versus “pork-and-miso” imoni the way other regions argue about ramen styles. Sendai, in neighboring Miyagi, has its own pork-miso take as well, so don’t assume every “imoni” you see on a Tohoku menu is identical.
The Riverside Imoni-Kai Tradition
What makes imoni culturally interesting isn’t just the recipe — it’s imoni-kai, the practice of cooking it outdoors in large groups, usually on a gravel riverbank. The tradition is said to date back generations, originally tied to harvest-season gatherings where farmers would cook taro and dried fish together near the water where they were washing the crop. Today it’s closer to a autumn barbecue: groups rent or bring a big pot, set up camp chairs, and spend a Saturday afternoon cooking, eating, and drinking by the river before the weather turns cold. The Mamigasaki River running through Yamagata City is the most famous site, with riverside sections getting so busy on autumn weekends that some areas require reservations through the city for cooking spots.
Yamagata’s Giant Pot Festival
The tradition’s biggest public showcase is the Nihon-ichi Imoni-kai Festival (日本一芋煮会フェスティバル), held on the Mamigasaki riverbed in Yamagata City, usually on the first Saturday and Sunday of September. The signature attraction is a genuinely enormous pot — several meters across — stirred with a construction crane fitted with an oversized ladle, cooking thousands of servings of imoni in one batch using tons of taro, beef, and soy sauce. Bowls are sold to the public for a nominal fee, historically around ¥300, though you should check the current price and exact dates on the Yamagata City tourism site each year since both can shift. Expect large crowds, food stalls, and a genuinely festive, slightly absurd atmosphere watching a crane stir soup.
Best Time to Go
Imoni is strictly a cool-weather, early-autumn food — this isn’t a dish you’ll find served fresh in summer or deep winter. The sweet spot is mid-September through late October, when the weather is cool enough to want hot soup outdoors but not so cold that riverside picnicking is miserable. Early September usually brings the giant festival; weekends through October are when ordinary imoni-kai groups fill the riverbanks. If you’re combining this trip with other Tohoku snow-country travel later in the season, Yamagata’s mountains get serious snowfall by December, which is also when the region’s backcountry becomes a destination for renting snowshoes for walks beyond the ski resorts — but that’s a different trip, well past imoni season.
How to Get to Yamagata
Yamagata City is reachable directly from Tokyo on the Yamagata Shinkansen (Tsubasa line), a roughly 2 hour 40 minute ride from Tokyo Station with no transfer, running on regular JR tracks rather than a fully dedicated shinkansen line. One-way fares run approximately ¥11,000–11,500 for an unreserved seat, less with a JR rail pass that covers the route. From Yamagata Station, the Mamigasaki riverbank festival site is about a 20–30 minute walk or a short taxi ride; local buses also run during festival weekends. If you’re building a wider Tohoku itinerary, the region’s other food specialties are worth detouring for — Hokkaido-bound travelers connecting through this part of the country sometimes also stop for Oshamambe’s famous crab rice ekiben, and Tohoku’s coastal rail lines offer their own worthwhile detour via the Sanriku Railway along the reconstruction line.
Where to Try Imoni Without Your Own Pot
You don’t need to organize a riverside cookout to taste imoni — plenty of options exist at every budget level:
- Budget: Attend the September festival and buy a bowl for a few hundred yen, or visit during a regular autumn weekend when community imoni-kai groups along the Mamigasaki sometimes welcome curious onlookers (never assume you can simply join and eat without asking first).
- Mid-range: Izakaya and local restaurants around Yamagata Station serve imoni as a seasonal set menu, typically ¥1,500–2,500 depending on whether beef or extra sides are included. Many only put it on the menu from September through November, so ask before assuming it’s available year-round.
- Splurge: Some ryokan in the Yamagata and Zao Onsen area work imoni-style taro dishes into their autumn kaiseki courses, and a handful of outfitters rent full riverside imoni-kai setups — pot, burner, folding tables, ingredients — for private groups, running upward of ¥5,000–10,000 depending on group size and whether staff cook for you.
If you’ve got downtime after soaking up the riverside atmosphere, the region’s onsen towns also have simple public foot baths worth a stop — see our guide to Japan’s free public foot baths for how to spot and use them without undressing.
Common Mistakes to Avoid
The biggest mistake is timing: imoni is a seasonal dish tied to the autumn harvest, and showing up in summer or winter expecting fresh riverside imoni-kai will leave you disappointed, even if a restaurant still serves a version off-season. Second, don’t confuse Yamagata imoni with Sendai’s pork-miso version and assume one recipe applies everywhere in Tohoku — ask which style a restaurant serves before ordering if you have a preference. Third, if you want to watch or photograph the giant-pot festival, arrive early; the best viewing spots near the crane fill up fast on festival mornings. Finally, remember that riverside imoni-kai spots during busy autumn weekends are sometimes reserved through the city in advance — wandering down expecting an open patch of gravel on a popular Saturday may mean a longer walk to find space.