The mournful chant of the ishi-yakiimo-ya or stone-roasted sweet-potato seller advertising his wares is a cherished part of the late fall and winter landscape in Japan. The sing-song chant is often accompanied by the thin, penetrating tone of a whistle, which seems to echo the sound of the wind. Braving the cold to rush out and buy a piping hot sweet potato wrapped in newspaper, holding it in freezing hands, blowing on it to cool it down while saying “Achi! Achi!” (“Hot! Hot!”) is a precious memory from my childhood.
Unfortunately , the ishi-yakiimo-ya vending cart is no longer as ubiquitous as it used to be, though with the recent nostalgia for the postwar Showa Era, they, along with other traditional street-side food vendors, may be making a slow comeback.
While several kinds of imo, the Japanese word for “potato,” are consumed in Japan — jagaimo (white potato), satoimo (taro), yamaimo (mountain yam) and more — the satsumaimo or sweet potato holds a special place in its culture and history.
The Satsuma part comes from the southern region of Kyushi which is present-day Kagoshima Prefecture, a subtropical land with rich farmland as well as the longtime international trading port of Nagasaki. Originating in South or Central America, the sweet potato entered Japan sometime in the late 16th century from China, probably via the kingdom of Ryukyu (present-day Okinawa). Cultivation of the tuber quickly grew in the southern Japan areas of Kyushu, Shikoku and southern Honshu, since it was well suited to the mild climates there. As early as 1719, a Korean envoy observed that steamed satsumaimo were being sold from open stalls in the then Imperial capital of Kyoto.
You’ve probably heard of the Irish Potato Famine of 1845-52, when millions of people starved to death or were forced to emigrate from Ireland because of massive potato-crop failures. In Japan 100 years earlier, the sweet potato saved people from dying of famine, rather than causing one.
In the mid-18th century, rice crops failed for several years running, particularly in the Kanto region. Since Edo (present-day Tokyo) was located in the Kanto region, this was a very serious matter for the Shogunate, for besides making people suffer, crop failures and hunger made them riot.
A man named Aoki Konyo, a scholar of both Confucianism and rangaku, the study of Western science and philosophy, experimented with growing satsumaimo plants from the south in gardens in the Kanto area. At the time the region was thought to be too cold to grow satsumaimo crops, but he was able to prove otherwise.
Satsumaimo crops spread rapidly, especially in the area directly north of Edo, which today is Saitama Prefecture, and which had been particularly hard hit by rice crop failures. In just a few years, the satsumaimo was well established as an alternative carbohydrate source, and Aoki came to be known as the “Potato God of Edo.”
You can still see signs of the gratitude people felt toward the humble satsumaimo to this day, in the form of several imodera and imo jinja, Buddhist temples or Shinto shrines dedicated to the tuber scattered around the Kanto area.
Just like apple-picking is a fixture of the fall months in many parts of the United States, imo hori (potato digging) is a rite of fall in Japan, and is especially popular as an outing for kindergarteners. A row of small, red-faced children pulling on a stubborn plant with all their might is quite a sight.
The typical Japanese satsumaimo has a bright red-purple skin and pale cream-colored flesh, which darkens to a light golden-yellow color when cooked. Popular named varieties include Beniaka, Beniazuma and Kintoki. (Beni means “scarlet,” and kin means “gold.”) The flesh is more starchy and a bit sweeter than the orange-colored American sweet potato.
A fairly recent development is the murasaki imo, or purple sweet potato, which has a startlingly deep purple color when cooked. Besides being eaten as is, it’s popular as a soft-serve ice-cream flavor and a natural food coloring.
Despite their sweet flavor, satsumaimo are often used in savory dishes such as stews and soups, and one of the most popular ways to enjoy them is to cook them with rice. This is called imo gohan (potato rice), a dish that would appear on the dinner table almost every day during the main satsumaimo season at my grandparents’ house in Saitama.
Another satsumaimo-based fixture of the colder months, especially in the Kanto region, is the daigaku imo (university potato) sweet-potato pieces that are deep fried then candied in a sweet-salty syrup and sprinkled with toasted sesame seeds. This snack probably originated in the small eateries that sprung up around the major university campuses that were established in the Tokyo area after the Meiji Restoration of 1868.
Daigaku imo was cheap, sweet and filling, perfect for hungry students. They are still a popular fall and winter street snack and are often served at fall school festivals; many people eat them as part of a meal, too.
On the opposite end of the dainty scale from daigaku imo is a Western-style dessert that is confusingly also called “suwīto poteto” (sweet potato), and consists of sieved satsumaimo with butter, cream, brandy and cinnamon, nutmeg or vanilla, which is stuffed into a small tartlet dish and baked until browned on top. It might be closest in flavor to an American pumpkin pie filling.
The easiest way to enjoy a satsumaimo is to simply steam or bake it. You don’t need a special roaster, although you can buy one if you want.
If baking, heat up the oven to a fairly low temperature, around 150 degrees C; this allows the sugars in the satsumaimo to develop as it cooks. Pop in your sweet potato, and bake until the skin starts to blister and a skewer or chopstick can be inserted into the middle easily. You may see a squirt of sugary syrup come out when it pierces the skin.
If steaming, use a steamer large enough to hold the satsumaimo, and cook until a skewer or chopstick goes through easily, about 30 minutes to an hour.
Satsumaimo are flavorful enough to eat without any additions, but some people like to add a sprinkle of salt or a little butter to counteract the sweetness.
Still, a home-cooked satsumaimo somehow doesn’t match the experience of buying a red-hot imo from an ishi-yakiimo seller. So if you’re lucky enough to hear that plaintive chant in the evening, grab your purse and chase after the cart. It’ll be worth it.