Rare sweet potato variety deeply rooted in Japan city

SAITAMA - The harvest season for beniaka, a traditional sweet potato variety, has arrived. I visited Saitama, the birthplace of the potato that has become rare these days.

In early October, I was standing by a field surrounded by houses in Minuma Ward, Saitama.

"It'll take a bit more time for the full-scale harvest," said Haruhisa Asako, 57, as he turned the soil in search of a vivid burgundy-skinned crop of beniaka.

"A scorching summer and lack of sunlight in the beginning of autumn made me worry if the crop would grow well, but it's grown better than I expected," he said. "I think the potatoes will grow even bigger."

The beniaka variety was discovered in 1898 in the village of Kizaki, which is now part of Saitama, by a farmer who came across a mutant type with beautifully coloured skin among a domestic variety that she harvested.

Beniaka became popular for its taste and appearance. In the 1930s and the '40s, beniaka were cultivated mainly in the Kanto region, with the crop acreage reaching 30,000 hectares.

During and after World War II, however, the number of farms cultivating beniaka declined rapidly. It became difficult for beniaka to be found on the market after beniazuma, a type that reliably delivers a big harvest, appeared in 1984.

Among the major production areas of sweet potatoes, Kagoshima Prefecture produces 330,000 tons a year, followed by Ibaraki and Chiba prefectures. Saitama Prefecture produced only 5,500 tons of sweet potatoes last year, but local farmers have started an effort to preserve the rare beniaka.

Asako and other farmers launched a group to study the beniaka variety in 2009. This year, group members planted the crop on about 50 acres of land.

Farmers in the town of Miyoshi, Saitama Prefecture, meanwhile, have also been working to promote local sweet potato varieties.

Beniaka is among varieties they ship under the common label "Tome no Kawagoe Imo" (Wealthy Kawagoe sweet potatoes), using the name of a nearby city famous for the produce.

Asako also produces the beniazuma. Compared to the mainstream variety, "The harvest of beniaka is smaller," he said.

According to Takeyo Noguchi, an official at the Saitama municipal government-run Minuma Green Center, beniaka are sensitive to soil texture, making it difficult to apply the correct amount of fertilizer.

Asako works hard to provide a better environment for the sensitive crop such as by using more nutrients.

Compared with other types, beniaka are vulnerable to bugs and hard to maintain in good quality for a long time after harvest. The green centre is keeping beniaka in a large storehouse to determine the best temperature and humidity to keep them for a long time.

Painstaking work is needed to cultivate beniaka, but the variety is definitely delicious, with a texture similar to chestnuts. The elegant and mild sweetness with a somewhat old-fashioned, simple flavor attracts many people, Asako said.

"It's delicious on its own, but it's also good as an ingredient," he said.

Local pastries use beniaka for making puddings and sweat potato pastes, while schools use it as ingredients in lunch for children.

"It takes time and effort to produce this variety," Asako said. "However, we should preserve the taste that is deeply rooted in this area."


Beniaka are rarely seen on the market. But you may find them at farmers' stands in Saitama or Miyoshi in the year of a big harvest.

Beniaka potatoes become sweeter and more delicious if they are allowed to age for a month or two after the harvest rather than eating them right away.

To keep them at home, Asako recommends they be dried for some time under the sun and wrapped with newspaper before being put in a corner of the kitchen.

They should not be kept in a refrigerator as they are vulnerable to cold. Beniaka potatoes cook fast, and should be steamed for a shorter time than other varieties. This characteristic makes beniaka well suited for tempura.