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Sweet Potatoes, Yams, and the Yam Bean

by Jacqueline M. Newman

Vegetables and Vegetarian Foods

Summer Volume: 2001 Issue: 8(3) page(s): 17, 18, 19, and 20

Tubers were probably the first plants man domesticated. The three detailed in this article, sweet potato, yam, and the yam bean, are all known in China today, but were not all known there in earlier times. The yam has been used there the longest, the sweet potato the newest import, and the yam bean’s length of time is open to question. The use of yams continues to decline in China while the use of sweet potatoes does not. The latter are China’s third most important crop after rice and wheat. Actually, in the past ten or fifteen years, the use of sweet potatoes as a staple has declined and been relegated to minor roles. The reason is that as people become more affluent, they use this and other tubers less and less.

These three tubers are discussed together in one article to help undo some of the confusion associated with them. They are presented in order of importance in China’s current dietary. Recipes for them will be provided in decreasing order of current use. And, keep in mind that though taste and texture will certainly change, each of these tubers can be substituted for any of the others in any recipe that includes one or more of them. That may add to your confusion, but we hope not.

SWEET POTATOES: are the earliest remains of a tuber not found in China, but in Peru. They are dated as more than ten thousand years old. These prehistoric vegetables were probably a hybridized version of a vegetable found even earlier in the northern part of South America. Though well known in China now, they did not make their way to Asia and on to China until thousands of years later and probably arrived using a variety of routes. The tale most frequently touted is that a Spanish explorer, in the early part of the 15th century, brought these vegetables to the Phillippines. Decades later, during a famine in the Fujian province, either an overseas merchant from Luzon in the Phillippines brought them to the then Governor, Hsuen-tseng in 1594, or the Governor sent an expedition to Manila or Luzon, where many Chinese were living, in search of food plants.

Still another view of their arrival is even earlier, when traders came to China with these tuberous vegetables from India; they went to Yunnan. Others say that traders came by boat to the port of what was then known as Chang-chou bringing sweet potatoes in to China via that route. Were these choices not enough to ponder, there is yet another report that the sweet potato was in Tali, near the Burmese border circa 1563; and that it came to China from there. Still another thought or report, they came via the Silk Road from Persia and/or Turkey.

No matter which is considered correct, all will agree that the sweet potato began its life in China called chin shu. That name held for those that were golden, the more common name today is hong shu or red potato. There are white sweet potatoes, too, and they are called bai yu; and sometimes one or another go by the names of shan yu or mountain tuber, di gua or earth melon, or even hong tiao or red trumpet creeper. Many people do confuse them with yams and so the sweet potato may also be called kan shu and even fan shu, the latter name politely means foreign tuber. With this large number of names, clarity of species is important, but often not known. No matter, these imports quickly supplanted the yam and other below-ground roots, rhizomes, or tubers; and they did so rather quickly because the Chinese were hungry and because they are not nationalistic when it comes to foods.

The Chinese do not resent eating or adopting imports as long as they adapt them to their own tastes and cooking styles. This makes new food items integral parts of their cuisine. So Iponoea batatas, the botanical name for this multi-colored, multi-faceted, plant with purplish flowers related to the morning glory, became popular very quickly.

The part of it that grows below ground is used as both starch and vegetable. It is dense and tasty, some say more so than the yam, which it rapidly but not completely replaced. Above ground, this flavorful vegetable food has delicious variously shaped leaves and they are loved but not consumed in very large amounts because to do so in very large amounts invites poisoning oneself.

Sweet potatoes grow in mountainous terrain and on flat, even sandy soil, and they grow in marshy and salty areas. Probably because of this and the fact that they mature rapidly, they quickly became a staple food in China. The need for them due to famine in so many locations, their speedy growth, and an Imperial edict that encouraged farmers to grow even more of them than they were made them easily available. As such, they were fed to young and old, and even to pigs, chickens, and dogs.

Today, China produces more than half the world’s crop of this tuber and they are used in most provinces and in many different ways. They are found on street corners baked and whole in winter where they are seen hanging on wires suspended over buckets and cooking over charcoal. In winter and during the rest of the year, they are used dried, pressed, or cut into rice-shaped pieces, shredded, steamed, rolled into strips, made into flour and noodles, even into teas, wines, distilled liquors, and more. In a myriad of ways, families at every economic level consume this commonplace food. Despite this widespread usage, sweet potatoes are not popular because they are considered food for the poor, many of whom eat them out of necessity three meals a day every day. So the affluent do not like it known that they, too, eat sweet potatoes.

In many regions of southern China and in the middle of the country, during and post fall harvest times, slices of this vegetable are found drying on hillsides and roadsides. They are referred to as 'sweet potato money' and as such, these discs are kept for use in winter when the price of fresh ones rise.

The best known recipes for them, like their use, transcends their image. They are found at all types of events from breakfasts to banquets held celebrating weddings. At the latter, that special meal might begin with Glazed Sweet Potato Balls, the tuber mashed and mixed with sugar to wish for a sweet life for the couple. They can have another starch mixed with them, be stuffed with another similar-wishing food such as sweet bean paste, coated with a thin batter, dipped in sesame seeds, and then deep-fried. The rest of the banquet meal might include Imperial Fragrant Duck made braised with or stuffed with sweet potatoes. An ordinary winter-style home meal we once were invited to in the Sichuan Province included Steamed Beef served on cubes of steamed sweet potato and meat, probably pork. For holidays, the sweet potato is made into a popular candy to be given to friends and relatives wishing them a sweet year.

The leaves of this vegetable are used as a green, often in small amounts as a base upon which another dish sits. They are also used in soups, and they are stir-fried with lots of garlic. The reason no one consumes the leaves in large amounts is because they do contain hydrocyanic acid. Eating small amounts is not a cause for worry any more than eating spinach is which contains oxalic acid.

Besides concern for the amount of leaves eaten, attention should be paid when buying sweet potatoes. Avoid those with cracks, spots, or bruises. This vegetable does not like the cold, so also avoid any that have been refrigerated. And, do not eat more than two of them or the equivalent amount of sweet potato skin, as that eaten in excess can also be problematic.

Sweet potatoes are considered sweet, their nature is neutral when cooked, and they are thought to be slightly cool if eaten raw; not a popular use in China, nor a real healthy one. Also known for their medicinal properties, the part that grows underground is used to relieve constipation, aid those with night blindness, and help reduce pain in nursing mothers with ulcers in their breasts. Eating them is said to improve a person’s qi as well as moisten their lungs and stomach. They are also considered an aid for urinary problems. The leaves are thought to reduce pus-infected regions, even eliminate them when used as a poultice. The leaves are also used to reduce coughs when cooked with lots of sugar and taken in small amounts.

This rather new vegetable to China, may not be loved by everyone there, and as indicated, some may not even admit they eat them. But actually they do, because in China many new manufactured foods have them as a component. They are used in them to help maintain the texture of the end-product.

YAMS: are often confused with the sweet potato and visa versa. Yams are starchier and less flavorful than the sweet potato; and they have a long history of use in China. They were known at least as early as Han Dynasty times (206 BCE - 220 CE), and they can be similar in size and shape to the sweet potato, but the relationship ends there. They are not as easy to use, do not cook as quickly; and in addition, many wild species of yams are toxic and therefore never eaten. Yams grow in wet or marshy or in dry-land areas, and many varieties of them require a long process of scraping and soaking before they can be consumed.

Botanically in the Dioscorea family, there are many different dry-land and wet-land areas. They are called shan yao meaning mountain medicine and are used for both food and healing purposes. They are also called shu yu or yam potato, shan yu or mountain potato, and huai shan or mountain food. Yam cultivation in Southeastern China was detailed thousands of years ago. Then, they were described as purple-skinned and thought to bestow longevity on those who ate them. Shortly thereafter, the Chinese used poisonous varieties of the yam as a means to catch fish.

It is important to know which variety of yam you are purchasing or at least be assured that that particular one is edible. One of the most popular ones used by the Chinese is Diascora esculenta, known as Asiatic Yam or the Fancy Yam. It has no toxicity but must be cooked a long time, as must many others. This yam is used in soups and stews, and is popular mashed and fried. Diascora alata or the Greater Yam, is also known as Air Potato; it is used boiled, roasted, baked, mashed, made into chips, and fried, and when made into a flour, used as a thickener.

You may know of this and other yams by an African name because the flour is used in many African countries; that is called fufu. This yam has aerial tubers or bulbils that are made into many different foods. Diascora opposita, known as the Chinese Yam, can grow in colder climates. It is also known by its aroma, as Cinnamon Vine. It is called wai shan and most often boiled, baked, grated, and made into noodles. Also known as the temperate variety yam, it does not bind well and is most often cut in pieces and cooked in soups and stews. It is also fried and can be used as a starch that bears the name Guiana arrowroot, but be aware that is a weak thickener.

Not very popular now since sweet potatoes became known in China, the yam was and is often found in Chinese poetry. We like when it was mentioned as a temptation and suggested to departed souls offering them promises of its earthly delight. Now, the yam is used for gaining strength, increasing appetite, for those with asthma, indigestion, and for diabetics. When used as a food, its flavor, considered sweet, is thought to act on lungs, spleen, and kidney. It is also believed that eating it can improve sexual energy.

YAM BEANS are a large food item that have many names. They are called 'cool potato' or liang shu, 'earth melon' or tu gua, 'bean potato' or 'potato bean' and duo shu and ge shu or 'kudzu potato.' The yam bean was known earlier in China as ko or fan ko and is botanically known as Pachyrhizus erosus. In the United States and much of the western world, this vegetable is known by its Spanish name, jicama, pronouncing the letter 'j' as an 'h' saying 'hicama.' It is popular in Mexico, Cental, and South America and known there as the 'Mexican water chestnut' and the 'Mexican turnip.'

Yam bean is a plant that confuses because the edible part is not a bean. Much has been written about this vegetable yet information about this botanical, whose name is Pachyrhizus erosus or P. tuberosus gets mixed up with the root sometimes known as the Oriental Yam Bean or kudzu. The latter is botanically known as Pueraria lobata. While the former is large and turnip-like, the latter is not and it is frequently consumed as flowers or leaves, the root made into noodles and used as a jelling agent.

This root vegetable has very large tubers that most often are somewhat like flattened balls, but there are round varieties that are confused with yams. As with most roots, the yam bean is eaten peeled and cooked. This particular food is sweet and can be eaten raw or cooked. The Chinese mostly cook it cubed or add it in a variety of shapes to many dishes. Sometimes it is used as a substitute for water chestnuts. When using it raw, young roots are the best as they are less fibrous than are the older ones. In western China, this root is grated and added to other dishes, also served raw and shredded and mixed with chili sauce, and made into a starch and used as a flour.

The leaves of the yam bean are best avoided as they are considered narcotic and more toxic than the leaves of the sweet potato. Medicinally, the seed and the tuber are used, the leaves are not. Chinese pharmacopeia touts the seed as something that can kill parasites and help in the cure of scabies. They do warn that the seed is poisonous and that it has an effect on the lungs. The tuber does not. It is said to promote the secretion of saliva, stop thirst, and affect the stomach. Its nature is believed warm, its flavor sweet.

Medicinally, this vegetable has considerable appeal because it is touted for those with chronic alcoholism, mixed with sugar and chewed several times a day. The Chinese do like the yam bean as medicine and they adore it as a vegetable, probably because it remains crunchy even after cooking. It is a popular starch in puddings and custard-like foods.

Below are several recipes for these underground wonders. Remember that one can be substituted for another in most instances. Enjoy them all.
The editor wishes to thank Laura Brown, a teacher in the New York City school system, for many of the materials she provided to her about the sweet potato.
Glazed Sweet Potato Balls
1 pound sweet potatoes
2 Tablespoons brown sugar
1 Tablespoon granulated sugar
1 cup flour
1 teaspoon sesame oil
1/4 cup sesame seeds
1 quart corn oil
1.Peel, quarter and simmer sweet potatoes until soft in a pot of hot water. Then drain and mash them.
2. Mix them with the sugars and half of the flour and the sesame oil. Roll into one-inch balls.
3. Mix flour with one-quarter cup of water mixing making a thin batter.
4. Heat corn oil until about 325 degrees F, then dip a few balls in the batter, then dip the top of the ball into the sesame seeds and deep fry until light golden in color. Drain and repeat until all of the ball are fried, then serve.
Yunnan Yam Stew
1/2 pound lotus root
1/2 pound yams
1/2 pound boneless beef shank, cut into half-inch slices
10 pitted Chinese red dates
3 Tablespoons fermented black beans
1 Tablespoon Lychee Chinensis or Chinese wolfberries (optional)
1 Tablespoon rice wine
2 Tablespoons yam or sweet potato flour or cornstarch mixed with two tablespoons cold water
1. Peel and sliced lotus root in half the long way then cut each circle in half. Repeat this process for the yams. Put both into a heat-proof casserole or Yunnan Pot.
2. Blanch the beef slices and add to the pot along with the dates, black beans, wolfberries, and the rice wine. Then add a scant cup of water and cover, put this casserole into a steamer over boiling water and steam for one hour. Then remove the casserole from the steamer.
3. In small pan, heat the flour/water mixture adding a half cup of the liquid from the casserole. When thickened return to the casserole, mix well and serve.
Spicy Fish with Yam Bean
1 pound boneless skinless flat fish fillets
1 egg white
1 Tablespoon ginger juice
1 Tablespoon cornstarch
1 cup corn oil
1 clove garlic, minced coarsely
12 Sichuan peppercorns
4 dried chili peppers, seeded and crushed coarsely
1 small yam bean, peeled and cut into thin strips
1 Tablespoon thin soy sauce
1 Tablespoon rice wine
1 Tablespoon Swatow wine vinegar
1 scallion, cut into one-inch pieces
2 Tablespoons coarsely chopped olive pits or almonds
1. Cut fish into one-inch by two-inch thin slices.
2. Mix egg white, ginger juice and cornstarch and marinate the fish in this mixture for twenty minutes. Heat wok, add oil then deep fry half of the fish at a time for three minutes. Repeat for the second batch. Do not overcook. When removing the fish from the oil, separate the pieces on paper towels so that they cool quickly. Discard all but one tablespoon of oil from the wok.
3. Heat remaining tablespoon of oil and add garlic, peppercorns, and yam bean and fry for one minute, then add soy sauce and rice wine and the fish and fry another minute until the fish is heated. Stir in the scallion pieces, stir and serve immediately garnished with the olive pits or almonds.

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