That bright platter of sticky-sweet candied "yams" - a long-treasured part of the Thanksgiving meal - is often not. Sweet potatoes are often colloquially referred to as "yams," and not just on Thanksgiving. True yams are biologically distant from sweet potatoes, although they are both tubers. Some people further insist that the redder, sweeter and more elongated Japanese varieties of sweet potatoes are "yams" while the paler, rounder, supermarket staple are sweet potatoes. In any case, you are unlikely to find yams in a conventional US grocery.
What are yams, then? And what sets them apart from the familiar, orange-fleshed winter vegetable we so often confuse them with?
A Brief History
Yams are a staple crop of West Africa, and have been grown there for 11,000 years. Anthropologists have dated grinding stones from Africa that may have been used to pound starchy yams back to over 100,000 years ago, even, in the Middle Stone Age. Slave traders who arrived in West Africa may have brought yams back to the Americas during their journeys. But once African slaves were in North America, they found sweet potatoes, native to the New World, as apt substitutes for yams.
Conversely, types of yams referred to as "mountain yams" have been eaten in Asia for thousands of years as well. Often found in Chinese herbal medicine, today one of the most popular Asian mountain yams is called naga-imo in Japanese. It's often grated, to serve as a delicacy with noodles and soups. The viscous texture of these yams, once grated, easily distinguishes them from less-starchy sweet potatoes and other tubers. Its generous starches are also used in batters or as thickening agents in Asian cuisines. Another popular variety is known as ubi or purple yam, the tubers of flowering water vines eaten throughout Southeast Asia.
- Yams can vary in size from that of an average potato to over 100 pounds
- In some West African languages, the word "yam" means "to eat."
- African countries were responsible for 96 percent of worldwide yam production as of 2007.
- The interior flesh of yam varieties can range in color from white to yellow to bright purple (as can those of sweet potatoes, adding to the confusion).
- In Ghana, yams are traditionally served to celebrate the arrival of a new baby.
Most yams grow in tropical and subtropical climates. Different regional varieties are popularly grown for food in Africa, South America, the Philippines, Vietnam, Japan, India and Nepal. These tubers grow from perennial vines in the plant genus Dioscorea, and may grow underground or under water. They are botanically related to water lilies and grasses.
Yams are a laborious crop to grow and store, as they are highly perishable once harvested in the warm climates in which they grow. Most types are produced for an annual harvest, taking six to ten months to grow. These plants thrive in hot and humid environments with plenty of rain, and may become dormant during annual dry seasons. (An exception to this is the mountain yam, which grows well in temperate zones and can withstand temperatures well below frost.) West African farmers do not typically buy new seed tubers each growing season, instead saving small yams and pieces of yams for planting the next season. As a result, any lingering diseases and pests from the first crop are passed onto the next year's, which can result in gradually failing yields and quality. The minisett technique was introduced in the 1970s to alleviate the situation, and involves treating the seed tubers with fungicide and pesticide before planting. This practice has been found to help increase the economic viability for small-scale African farmers in recent years. However, in famine-stricken areas of Africa, the seed tubers that are generally set aside for planting the next year are sometimes consumed in desperation, leading to the destruction of yam cultivation.
As a perennial plant, yams can be cultivated at any time of year, but they are often treated as an annual crop. In West Africa, yams are commonly planted at the beginning of the warm, rainy season and harvested in early autumn of the next one. Peoples such as the Ashanti and Igbo celebrate the harvest of yams with an annual celebration lasting days. Other yams like the mountain yam are winter crops that are planted at the beginning of the cold season and harvested the following autumn or winter.
Requiring about one year and plenty of water to grow, yams are highly susceptible to pest, fungus and diseases. Infected plants have been known to wipe out entire crops in places like Nigeria in recent years. As a result, many studies have been undergone to understand and manage yam healthiness. Another contributing factor to crop failure lies in the storage of yams after harvest; diseases like dry rot can easily destroy yams post-harvest if they are not properly stored and handled. To counteract these threats, yam crops have been treated to a number of chemical pesticides (such as in the minisett technique), both during its growth and post-harvest. It can be difficult to locate or determine non-chemically treated yams in the US market, since they are seldom found outside of small, ethnic groceries. (*And check out our Real Food Rule of Thumb for more information.)
Characteristics and What to Look For
Yams are distinct from other tubers like potatoes for their hairy, rough surface. Most varieties have a more tube-like shape and they can grow quite long and fibrous if not harvested on time. Its flesh is typically starchier and less sweet than sweet potatoes, and can be ground into starches and flours. Yams are seldom eaten raw, except as grated fresh mountain yam, and have a mildly sweet flavor. They are extremely versatile and varied plants, having unique culinary associations throughout the world. However, like potatoes, they are most commonly eaten by boiling, baking or roasting.
Yams are primarily eaten as a source of carbohydrates, but they provide many health benefits in addition to filling one's belly. They are high in fiber, Vitamin C, B-vitamins and potassium. (Unlike sweet potatoes, however, they are not a major source of Vitamin A.) Yams are also associated with intestinal health thanks to their high fiber content, and may help alleviate pains associated with inflammation and the menstrual cycle. Traditional Chinese medicine has long used yams to treat stomach conditions such as indigestion and poor appetite, and for kidney and spleen health.
What to Do with It and Cooking
Yams can be prepared much like potatoes or sweet potatoes--even deep-fried in wedges like French fries. In addition to boiling, roasting or baking them, they can be mashed or pounded into thick soups or porridges, such as the traditional fufu or African porridge. They can be fried and served with a spicy dipping sauces, like the Nigerian dundu. Purple yams are used to make a popular Vietnamese soup. When not used for medicine or for grating onto dishes, mountain yams can be sliced thinly and dressed for a salad. And of course, they can be baked in casseroles with a sweet glaze, such as with candied yams.
Yams are traditionally stored in cool, dark earthen pits before being shipped to market. When you purchase yams, choose ones that are not bruised, visually blemished or discolored, and store for up to two weeks in a cool, airy dark place. If stored too long, they may begin to sprout (like other tubers). They are not recommended for refrigeration or for keeping covered in plastic, to discourage rot or the growth of mold.
Wild African Yam Stew
(from Plant Based Katie)
1 onion, chopped
1-2 tablespoons minced Anaheim pepper
1 tablespoon ginger, ground
1 tablespoon garlic granules
2 teaspoons ground cumin
2 teaspoons ground coriander
1⁄4 teaspoon crushed red pepper
6 medium yams or sweet potatoes, peeled and chopped
2 cups water
24 ounces chopped tomatoes
1 can (15 ounces) garbanzo beans, drained and rinsed (or 1½ cups)
1 can (15 ounces) black eyed peas, drained and rinsed (or 1½ cups)
1⁄2 cup almond or peanut butter, unsweetened
1 1⁄2 cups organic corn
1 bunch of collard greens or kale
- In a large pot over medium heat, add onion and pepper, but no oil. Cover with lid to keep the moisture released from the veggies in the pan. Stir frequently to prevent the veggies from sticking. Add ginger, garlic, cumin, coriander and red pepper. Cook for a couple more minutes, continuing to stir.
- Mix in yams, water, tomatoes, beans and nut butter. Bring to a boil, reduce heat and simmer for 20 minutes.
- Stir in corn and collards. Cook for about 10 more minutes, until yams and greens are tender.
- Serve over brown rice or other whole grain.
Lamb, Yam and Butternut Squash Soup
2 tbsp vegetable oil
2 lb stewing lamb (or mutton)
2 large onions, chopped
1 scotch bonnet chili pepper, chopped
3 beef stock cubes
1⁄2 large yam
1lb butternut squash
3 large potatoes
1 pint chicken noodle soup
1 bunch spring onions, sliced
1 bunch thyme, leaves only
Dumplings, to serve (optional)
- Heat the oil in a large pan. Add the lamb (or mutton) and cook until browned on all sides.
- Add the onions and chilli to the pan and cook until softened.
- Meanwhile, make up a jug of stock with the three beef stock cubes and about 1 pint 12 oz of boiling water, according to taste. Add the stock to the pan and simmer for 40 minutes until the meat is tender.
- While the soup is simmering, chop the yam, butternut squash and potato into pieces.
- Heat the chicken noodle soup in a separate pan add the yam, butternut squash and potatoes. Cook the vegetables until tender. When they are cooked all the way through, drain and reserve the liquid.
- Once the meat is tender, add the vegetables to the first pan and add some of the chicken noodle soup liquid if necessary.
- Scatter the spring onions over the soup along with the thyme leaves.
- Serve hot with dumplings if desired.
(*Real Food rule of thumb: We think that first and foremost, in terms of nutrition, people should eat lots of fruits and vegetables whether they are organic or not. The EWG's guide is a handy list, but we will point out here that the impacts of pesticides are not limited to your ingestion of them - agricultural chemicals also affect farmworkers and local waterways, both good reasons to buy organic, even those vegetables that carry a light pesticide load. Also, it has been demonstrated that produce grown by small-scale farmers, even those who are not certified organic, tends to have a lighter pesticide load than its industrially-produced counterpart, owing to industry's tendency toward large monocrops.)
This post was originally published in December 2014.