Yam is the common name for some species in the genus Dioscorea (family Dioscoreaceae). Although sweet potato (Ipomoea batatas) has traditionally been referred to as a yam in parts of the United States and Canada, it is not part of the Dioscoreaceae family.
I. batatas – the sweet potato is the only crop plant of major importance—some others are used locally, but many are actually poisonous. The sweet potato is only distantly related to the potato (Solanum tuberosum) and does not belong to the nightshade family. I. batatas is one of the approximately 50 genera and more than 1,000 species of Convolvulaceae, the morning glory family. Its large, starchy, sweet-tasting, tuberous roots are a root vegetable. The young leaves and shoots are sometimes eaten as greens.
Differences between Yams & Sweet Potatoes
Specific types of yams include Dioscorea alata (Hawaiian yam), Dioscorea batatas (korean yam) and Dioscorea esculenta (sweet yam).
There are approximately 200 different varieties of yams with flesh colors varying from white to ivory to yellow to purple while their thick skin comes in white, pink or brownish-black . Their shape is long and while their exterior texture is rough and scaly. Yams are closely related to lilies and grasses. Native to Africa and Asia, yams vary in size from that of a small potato to a record 130 pounds (as of 1999). Compared to sweet potatoes, yams are starchier and drier. Sweet potato varieties are classified as either ‘firm’ or ‘soft’. When cooked, those in the ‘firm’ category remain firm, while ‘soft’ varieties become soft and moist. It is the ‘soft’ varieties that are often labeled as yams in the United States.
Creamy or firm when cooked, yams have an earthy, hardy taste and usually a minimal amount of sweetness. Yams should be cooked rather than eaten raw. There are many ways of cooking it – barbecued, roasted, fried, grilled, boiled, baked, smoked and when grated it is processed into a dessert recipe. Research has shown some nutritional advantages to roasting over boiling when it comes to yams, so if you are deliberating over these two cooking methods, we recommend that you choose roasting. At the same time, however, when it comes to a potentially problematic substance like phytic acid (phytic acid can sometimes block absorption of desirable nutrients like zinc and iron), a wet-heat cooking method might be helpful. Because steaming is a wet-heat method that avoids submersing the food in water and risking excessive leeching of water-soluble nutrients, we recommend steaming over boiling when using wet heats (and we always stick with steaming in our own yam recipes).
Nutritious values:
Yam’s importance in the diet of the people in Nigeria and West African countries cannot be overemphasized. It contributes more than 200 calorie per person per day for more than 150 million people in West Africa while servicing as an important source of income to the people. Yam is an attractive crop in poor farms with limited resources. It is rich in starch, and allows many recipes. Yam is also available all year round making it preferable to other unreliable seasonal crops. These characteristics make yam a preferred food and a culturally important food security crop in some sub-Saharan African countries.
Besides simple starches, sweet potatoes are rich in complex carbohydrates, dietary fiber, beta-carotene (a provitamin A carotenoid), vitamin C, vitamin B6, manganese and potassium. Pink, yellow and green varieties are also high in beta-carotene.
Sweet potato varieties with dark orange flesh have more beta carotene than those with light-colored flesh, and their increased cultivation is being encouraged in Africa, where vitamin A deficiency is a serious health problem. A 2012 study of 10,000 households in Uganda found that 50% of children who ate normal sweet potatoes suffered from vitamin A deficiency compared with only 10% of those on the high beta carotene variety.
Choose yams that are firm and do not have any cracks, bruises or soft spots. Avoid those that are displayed in the refrigerated section of the produce department since cold temperature negatively alters their taste. Yams should be stored in a cool, dark and well-ventilated place where they will keep fresh for up to ten days. They should be stored loose and not kept in a plastic bag. Keep them out of exposure to sunlight or temperatures above 60°F (around 15°C) since this will cause them to sprout or ferment. Uncooked yams should not be kept in the refrigerator.
Health Benefits:
Protection Against Cardiovascular Disease and Osteoporosis
Yam provides around 110 calories per 100 grams of product. Yam is high in vitamins C and B6, potassium, manganese and dietary fiber while being low in saturated fat and sodium. A product that is high in potassium and low in sodium is likely to produce a good potassium-sodium balance in the human body, and so protects against osteoporosis and heart disease. Yams are a good source of vitamin B6. Vitamin B6 is needed by the body to break down a substance called homocysteine, which can directly damage blood vessel walls. Individuals who suffer a heart attack despite having normal or even low cholesterol levels are often found to have high levels of homocysteine. Since high homocysteine levels are signficantly associated with increased risk of heart attack and stroke, having a good supply of vitamin B6 on hand makes a great deal of sense. High intakes of vitamin B6 have also been shown to reduce the risk of heart disease.
Yams are a good source of potassium, a mineral that helps to control blood pressure. Since many people not only do not eat enough fruits and vegetables, but also consume high amounts of sodium as salt is frequently added to processed foods, they may be deficient in potassium. Low intake of potassium-rich foods, especially when coupled with a high intake of sodium, can lead to hypertension. Dioscorin, a storage protein contained in yam, may also be of benefit to certain individuals with hypertension. Preliminary research suggests that dioscorin can inhibit angiotensin converting enzyme, which would therefore lead to increased kidney blood flow and reduced blood pressure.
Yam products generally have a lower glycemic index than potato products.
Blood Sugar and Weight Control
Yams’ complex carbohydrates and fiber deliver the goods gradually, slowing the rate at which their sugars are released and absorbed into the bloodstream. In addition, because they’re rich in fiber, yams fill you up without filling out your hips and waistline. And one more benefit, yams are a good source of manganese, a trace mineral that helps with carbohydrate metabolism and is a cofactor in a number of enzymes important in energy production and antioxidant defenses. You’ve just got to hand it to Mother Nature; when She brings forth a food, She makes sure it integrates everything needed to contribute to your health and vitality.
Yams in different countries
– Japan
In Japan, the purple yam is popular as lightly deep fried tempura as well as being grilled or boiled. Additionally, the purple yam is a common ingredient of yam ice cream with the signature purple color.Yamakake is a yam-based Japanese dish prepared from tororo and maguro.
Another variety of yam, Jinenjo, is used in Japan as an ingredient in soba noodles.
– India
In central parts of India, the yam (Khamalu or Chupri alu) is prepared by being finely sliced, seasoned with spices and deep fried. In southern parts of India, the vegetable is a popular accompaniment to fish curry. In Assam, it is known as Kosu (কচু) and is normally boiled, mashed and lightly seasoned with salt.
Also eaten in India, Dioscorea alata, a purple-pigmented species, is known as ratalu or violet yam.
In the southern part, especially in Kerala, you can see both Purple and White colour Yam, Locally known as “Kaachil or Kavuttu”.
Dioscorea alata, known as purple yam and many other names, is a species of yam, a tuberous root vegetable, that is bright lavender in color. It is sometimes confused with taro and the Okinawa sweet potato (Ipomoea batatas cv. Ayamurasaki). With its origins in the Asian tropics, D. alata has been known to humans since ancient times.
In folk medicine, D. alata has been used as a laxative and vermifuge, and as a treatment for fever, gonorrhea, leprosy, tumors, and inflamed hemorrhoids.
– Nepal
Dioscorea root is traditionally eaten on Māgh Sankrānti (a midwinter festival) in Nepal. In Nepali it is called Śakhar Khaṇḍ and in Newari Hī. It is usually steamed and then cooked with spices…
