Sweet Potatoes: Japan's Enduring Sweetheart

Pile of sweet potatoes
(Photo courtesy of Ibaraki Prefecture.)

   As the fall breeze starts to blow, many Japanese people find themselves craving for sweet potatoes. But while sweet potatoes are undoubtedly an iconic taste of fall to people in Japan, in recent years, their deliciously sweet flavor has started to be enjoyed all year round as well. Let's find out more about the allure of sweet potatoes, a crop near and dear to Japanese peoples' hearts since long ago.

The Sweet Famine Fighter

   Sweet potatoes are root vegetables that originate from Central America, and found their way over to Japan sometime around the 1600s. In Japanese, they came to be known as "satsuma-imo" because they spread to mainland Japan from the Satsuma region (now part of southern Kyushu) in the south of the country. In 1732, Japan's shogun (the military commander-in-chief who ruled Japan at the time) strongly encouraged people to cultivate sweet potatoes as a so-called "emergency crop" that could act as a back-up if rice harvests turned out poorly — or worse, failed entirely and caused a famine. This is what led to sweet potatoes being grown in every region of Japan. Capable of growing even in poor or depleted soils and highly nutritious to boot, sweet potatoes have proven time and again to be a key source of nutrients whenever Japan has been hit by food shortages.

Sweet potatoes with reddish-purple skin and yellow flesh are the most widespread varieties in Japan.

Harvesting plump and fully grown sweet potatoes out of the soil. (Photo courtesy of Ibaraki Prefecture.)

The Root Vegetable That All Ages Root For

   Unlike regular potatoes, the sugar content of sweet potatoes increases when they're cooked, with some varieties even surpassing fully ripe bananas for sweetness. Because of this, they're often used in treats, sweets and candies as well. To Japanese people, sweet potatoes have a long and beloved history as a snack.

   In the past, sweet potato varieties like Naruto Kintoki and Beniazuma, which have low water content and a soft, flaky texture similar to chestnut, were the most commonly available types. However, advancements in selective breeding have given rise to sweeter and moister varieties like Anno Imo and Silk Sweet, which have more of a gooey and sticky consistency. There are currently as many as 60 varieties in circulation, so you can pick out whichever type suits your fancy.

Sweet potatoes come in lots of different varieties. Some specialist stores even let you taste and compare different types for flavor and mouthfeel. (Photo courtesy of Yakiimo Marujun.)

   Sweet potatoes are used to make a wide range of dishes loved by kids and adults alike. For example, they can be coated in batter and deep-fried to make tempura, steamed, sliced and dried in the sun to make hoshi-imo, or cut into long, thin French-fry strips, deep-fried and candied to make a sweet snack called imo-kenpi. They can also be used to make imo-jochu, a type of alcoholic spirit that utilizes their natural sugars in the distillation process.

Sweet potatoes are one of the most popular ingredients for tempura.

Hoshi-imo is made by drying sweet potato slices in the sun, which concentrates their natural sweetness without needing to add more sugar.

Imo-kenpi has a deliciously crunchy texture.

Imo-jochu has a high alcohol content, so many people like to drink it diluted with hot or cold water.

   Because they're grown all across the country, digging for sweet potatoes is an annual fall tradition for many of Japan's kindergartens and elementary schools. Eating a sweet potato that you've gathered yourself is a good way of learning about how crops grow, and gives kids a first-hand experience of the joys of harvesting. For many Japanese people, sweet potatoes are a crop that's been near and dear to them since their childhood.

Digging for sweet potatoes is a fall tradition that many Japanese people experience in their childhood.

Yaki-imo Baked Sweet Potatoes Are in Hot Demand Around the World!

   One delicious way of cooking sweet potatoes is to make them into yaki-imo by baking them with the skin left on. Not over an open flame or in an oven, though — the best way is to immerse them in piping-hot stones. When left for long enough, the far-infrared waves radiated from the stones gently cook the potatoes through, increasing their sugar concentration and removing excess water to bring out the natural sweetness.
   In the past, the only way to buy sweet potatoes baked in this way was from food trucks fitted with specialized stoves, which drive around towns and cities selling freshly baked sweet potatoes in the winter. As they work their way through the streets, the vendors shout out "STOOONE-BAAAKED SWEET POTATOOOES" ("ISHIYAAAKI-IMOOO" in Japanese) in a distinctively tuneful way that attracts droves of customers to their trucks. These days, there are also electric ovens capable of producing similar results to stone-baking, and baked sweet potatoes are sold at supermarkets all year round too, so they've never been easier to enjoy.

Piping-hot yaki-imo baked sweet potatoes, still in their skins. They smell sweetly fragrant and appetizing. (Photo courtesy of Ibaraki Prefecture.)

The sweet potatoes are slowly cooked by the far-infrared waves radiated from the hot stones.

Freshly baked sweet potatoes are moist and sticky on the inside.

Traveling food trucks selling stone-baked potatoes are a hallmark of Japanese winters.

   In recent years, there has been a surge in the popularity of yaki-imo baked sweet potatoes in South East Asian countries such as Thailand and Indonesia, where Japanese varieties are now sold in stores. The distinctive sweetness of Japanese sweet potatoes, combined with baking methods that really draw that sweetness out to its fullest, seems to be capturing many hearts in this part of the world.

Baked sweet potatoes are becoming popular in South East Asia.

   Another thing that's gaining popularity is chilled baked sweet potatoes, which are cooled in a refrigerator after they're baked, then sold cold. Chilling them gives them an even moister texture and sweeter taste, elevating them to a new level of deliciousness loved not just by those in Japan, but by people all over South East Asia too. And that's not all: the many carbohydrates found in sweet potatoes soften up and become easier to absorb into the body when they're chilled, which can help prevent blood sugar spikes, among other health benefits. It's no wonder they're proving such a hit.

The humble sweet potato has had modern makeovers in more and more fancy sweets and treats, including French 'Mont Blanc' desserts and elaborate parfaits. (Photos courtesy of Oimoya, Emporio Armani Caffe Omotesando.)

   Cakes, parfaits, shaved ice, custard puddings — the variety of desserts made with sweet potatoes is increasing, and there are even specialist stores just for sweet potato desserts. As new varieties of sweet potatoes emerge, along with new ways of enjoying them, their appeal will only grow bigger and brighter. Japanese people's love for sweet potatoes shows no signs of slowing down.