By Steven Crook and Katy Hui-Wen Hung

“My grandmother cringed at the very mention of sweet potatoes. She was born and raised in Tainan, and when she was growing up, sweet potatoes were all her family could afford to eat. In later life, the thought of eating sweet potato in any form repulsed her. Even in the 1970s, when I was a teenager, she was still like that. When we went to AoBa Chingye (青葉), Taipei’s pioneering Taiwanese cuisine restaurant, and she saw sweet-potato congee on the menu, she flinched. My mother, however, adored Japanese golden sweet potatoes (日本金時地瓜). They were just the right size for a healthy snack, and could be eaten without having to remove the skin.”

— Katy Hui-wen Hung

Taiwanese have been eating sweet potatoes since at least 1603, when Chen Di (1541–1617), a scholar who accompanied an anti-pirate expedition to Taiwan in that year, noticed indigenous people growing them. But the tuber, known to scientists as Ipomoea batatas, was likely a very recent addition to the local diet.

First domesticated in Central America around five millennia ago, the sweet potato was introduced to the Philippines by the Spanish in the second half of the 16th century. It reached the Chinese mainland sometime between 1582 and 1594. Recognizing that it could help feed the country’s growing population, Ming dynasty officials in famine-prone parts of China encouraged its cultivation.

The sweet potato probably reached Taiwan from Fujian soon thereafter. Yet there is also a chance that seafarers whose Austronesian ancestors had migrated eastward across the Pacific carried it back west after reaching South America. There is even a third possibility, because sweet potatoes found in the Cook Islands have been carbon-dated to 1000 A.D. – and very recent evolutionary scholarship suggests it was “present in Polynesia in pre-human times.”

Whenever and however it reached Taiwan, Ipomoea batatas had emerged as a key crop by the 1700s. Han pioneers spreading out across the western lowlands grew sweet potatoes as a stopgap while converting wilderness into paddy fields. In the early 18th century, a dock in Tainan was called “Sweet Potato Port” because it was a major commodity shipped from there to Fujian.

Unlike rice, sweet potatoes can easily be grown on hillsides, so it soon became part of the aboriginal diet. Among the Bunun people, there was a taboo against eating millet and sweet potato at the same time. Even today, some Taiwanese refer to this tuber as fānshŭ (番薯, “barbarians’ potato”), but the most common – and politically correct – term is dìguā (地瓜). The Holo name, hanji, is often rendered in Zhuyin Fuhao as ㄏ ㄢˇ ㄐ ㄧˊ.

George L. Mackay, the Canadian missionary active in northern Taiwan between 1872 and 1901, observed that farmers typically planted sweet potatoes in September or October, after the year’s second rice harvest. Part of the crop was cut up and dried under the sun for use throughout the year.

During Japanese rule, the colonial authorities famously emphasized the production of sugar and rice in order to satisfy consumers in the home islands. Not so well known is the great expansion of sweet-potato farming during that era. According to Economic Development of Taiwan: Early Experiences and the Pacific Trade Triangle by Frank S.T. Hsiao and Mei-chu Hsiao-Wang, sweet potatoes sustained both humans and hogs throughout the colonial period, and was a raw material for producing alcohol.

Ipomoea batatas “was the third important crop [after rice and sugar],” they write, and from 1934 to 1938 Taiwan was responsible for “3.7% of world production, and ranked fourth in the world behind China, Japan, and the United States… Despite this large output, most sweet potatoes were used domestically. On average, only 2.6% of production was shipped to Japan.”

In households that could not afford rice, sweet potato was boiled to make a porridge or was added to soups. In families that were a little better off, chunks were mixed in and steamed with rice to reduce the amount of the expensive grain.

Due to rice shortages during and for a while following World War II, the formula for locally made rice wine was adjusted to include sweet-potato mash. Into the 1960s, a cheap spirit with a high ethanol content, widely known by its Holo name of thài pe̍h chiú (太白酒) sold well.

Often made from sweet potatoes (it could also be made from rice, and was originally produced from cassava), it was delivered in large jars and sometimes sold by the glass at dry-goods stores. Farmhands and laborers brought their own cups, so they could enjoy a snifter at the end of the work day. As it was what economists call an “inferior good,” production of thài pe̍h chiú ceased in the 1970s when rising living standards meant ordinary folk could afford better beverages.

Despite the association with poverty, a dependence on sweet potato is preferable in some respects to a dependence on rice. As recently as the 1950s it was reported that indigenous children for whom the tuber was a staple were less likely to suffer from thiamine deficiency (which can lead to beriberi), compared to Han youngsters on the lowlands who mainly ate rice.

Taiwan’s sweet-potato production surged throughout the 1950s and 1960s, driven not by human appetite but demand for swine fodder. The 1969 crop was 3.701 million tonnes. By 1977, however, production had halved as livestock farmers embraced corn-based feeds. Over the past decade, around 10,000 hectares of farmland – most of it in Yunlin and Changhua Counties – has been devoted to sweet potato. Annual production has varied between 205,868 tonnes and 241,694 tonnes.

After the Republic of China government relocated to Taipei in 1949, the sweet potato became a symbol of běnshěngrén (本省人, “people native to this province,” the descendants of Han migrants who settled in Taiwan before 1945). At the same time, taro is a code word for wàishěngrén (外省人, “people from outside the province,” those born on the Chinese mainland and their offspring).

In 2000, when Chen Shui-bian became the first non-Kuomintang president in Taiwan’s history, the dessert served at his inauguration banquet was a taro and sweet-potato cake, symbolizing a desire for ethnic harmony.

Chinese-cuisine specialist and cookbook writer Carolyn Phillips suggests that the way in which sweet potato is baked as a street snack reveals a Central Asian influence on Chinese foodways that reached Taiwan after World War II. In her blog, Madame Huang’s Kitchen, she reminisces about a particular sweet-potato vendor in Taipei who used a concrete barrel, “shaped sort of like a traditional tandoori oven…Hot charcoal covered the bottom and vibrantly orange sweet potatoes were hung by hooks around the rim; they would slowly bake into a tender lusciousness as their bottoms roasted over the slow fire and the skins turned a crispy black.”

“When cooked properly, the potatoes will ooze with juices that will first caramelize and then burn,” she raves. “It doesn’t really matter whether you take them out covered with their natural caramel or allow the juices to turn black. It’s all a matter of personal taste.”

Sweet potatoes cooked the traditional way are still a common sight in towns and cities. Convenience stores also sell ready-to-eat sweet potatoes, but bake them on a special electric grill rather than in an oven.

Numerous varieties

For many people, a sweet potato is simply a sweet potato, but those in the food industry are familiar with the different cultivars that are grown in Taiwan. Certain ones are better for baking, others have more delicious and nutritious leaves, and some are processed into starch.

Sweet potato starch is what gives many of Taiwan’s thicker soups (羹, gēng) their viscosity. It is also a key ingredient of oyster omelets (蚵仔煎, usually known by their Holo name, ô á choan), creating their distinctive chewiness. For the same reason, sweet potato flour is often part of the mixture used to bread popcorn chicken (鹽酥雞, yánsūjī).

Different cultivars fetch very different prices, says Ignacio Chang, a manager at Taiwan Sweet Potato International Food Co. The Tainong 43, 44, 45 and 48 varieties – “almost totally without sweetness” but good for making starch powder – are very cheap. For Tainong 57, a popular cultivar for baking and immediate consumption, “the price directly from the farmer is about NT$15 per kg.”

Tainong 57, also known as the golden sweet potato (黃金甘藷), has brown skin and yellow flesh. The flesh of Tainong 66 – the red-heart sweet potato (紅心尾仔番藷 or 紅心地瓜) – is purplish.

The Tainong varieties were developed at the Chiayi Agricultural Experiment Station, a branch of the Taiwan Agricultural Research Institute (TARI). The Chiayi station has been researching Ipomoea batatas since 1922, and continues to release new consumer-friendly cultivars. One of the most recent, Tainong 74, can be stored at room temperature for at least 28 days without sprouting, and so is ideal for exporting to distant markets.

The World Vegetable Center (formerly called the Asian Vegetable Research and Development Center, AVRDC) in Tainan’s Shanhua District was for 20 years a sweet-potato research center of global importance. “Throughout Asia, sweet potato tubers have been an important staple food, and from its founding in 1971, the center conducted research on sweet potato,” says Maureen Mecozzi, the center’s director of communications and information. “By 1973, the center had more than 1,600 accessions of the crop.”

In 1987, the Consultative Group on International Agricultural Research (CGIAR) elevated sweet potato to the status of a high-priority crop. “It was considered under-researched and of vital importance to poor people in many developing countries,” Mecozzi explains.

“The International Potato Center in Peru began intensively researching the sweet potato,” he says. “After 1991, when the AVRDC board of directors decided to halt our sweet potato breeding program because it was costly to maintain, the entire AVRDC sweet potato collection was duplicated and transferred to the International Potato Center, and also to TARI.”

Ignacio Chang’s company sells a cultivar it calls the Taiwan golden sweet potato, grown by contract farmers in Yunlin County. “It’s a hybrid of Japanese and Taiwanese sweet potatoes,” he says. “The skin is purple, and inside it’s bright yellow. From the farmer, the price is around NT$21 per kilo, the highest of any variety on the market now.”

Around 20% of Taiwan Sweet Potato’s output is exported to Singapore and a similar amount to Hong Kong, Chang says. About 40% is sold in Taiwan as whole sweet potatoes, with the remainder turned into ice cream, syrup, chips, and other processed foods.

Chang encourages his customers to eat Taiwan golden sweet potatoes complete with their skin, to get the maximum amount of soluble fiber (which helps you feel fuller and reduces constipation) and flavonoids (some of which have an anti-inflammatory effect). His company uses a micro-bubble ozone system to wash the sweet potatoes, to ensure they leave the packing plant as clean as ready-to-eat lettuce.

According to Chang, there are several reasons why the sweet potato has made a gradual comeback. One is that the tuber and its leaves are no longer negatively associated with pig feed. Also, Chang says, more and more people have discovered the delightful taste of sweet potato, and that it can help one’s digestion. Because they can be bought ready-to-eat in convenience stores, there is no need to seek out a roadside vendor. Most importantly, perhaps, medical studies have identified several health benefits for those who eat sweet potato.

On March 26, 2013, Self, the U.S. women’s wellness magazine, declared the tuber to be their “superfood of the week,” noting that “one medium sweet potato has a mere 105 calories and four grams of filling fiber. Plus, one of these spuds provides a whopping 400% of your daily value of Vitamin A to boost your eye health and immunity.”

However, an article published in the Health section of the local Chinese-language United Daily News website on June 21, 2018 named baked sweet potato as one of six foods that are not as healthy as many people believe.

Once considered unfit for human consumption, sweet-potato stems and leaves are now a popular side dish. Cultivars bred specifically for their leaves, such as Tainong 71 and Taoyuan 2, are rich in vitamins C and B6, and far less bitter than previous iterations.

The Chinese-language website icook.tw, which has compiled more than 160,000 pages of food preparation tips, includes recipes for several popular sweet-potato snacks and dishes. Among the 2,179 entries mentioning dìguā are pages on how to make French fries and lasagna using sweet potato, as well as an unusual recipe for sweet-potato balls (地瓜球, dìguā qiú). Deep-fried, golfball-sized sweet-potato balls are sold in many night markets, but this version incorporates cheese to add complexity to the flavor.

Neither Taiwanese people nor their livestock eat sweet potato in the quantities they once did. In one place, however, the tuber plays the exact same role it did a hundred or more years ago. At Jiaba Shuangzhong Temple (嘉邑雙忠廟) in Chiayi City, the pious propitiate a horse deity. It is said that, if the horse is not well fed, it will break free and trample crops. So far, grass, drinking water, and sweet potatoes seem to have kept it satisfied.