Yams, Dioscorea sp.

In some African countries, yams are an important staple food. It is therefore held in high esteem and celebrated in many of these countries. The ‘New Yam Festival’ in Nigeria, for example, which is celebrated during the yam harvest, is famous. In some cases, the newly harvested yams are not eaten until the New Yam Festival has been celebrated.

Yams – a giant tuber

Yams (Dioscorea), also known as yam or yam root, are a plant genus within the yam family (Dioscoreaceae). There are currently around 800 different species of yam known, which are mainly found in the tropics. Some species are important food and medicinal plants.

Yams are mainly grown on small farms; rarely on large farms that grow yams exclusively. Propagation is vegetative through small daughter tubers or pieces of large tubers. The plant grows as a twining shrub and grows up to six meters high. Its leaves are heart-shaped. During cultivation, supports are needed to allow the shoots to twine upwards. For optimum growth, they need a temperature of 25 to 30 degrees Celsius; they generally need at least 20 degrees to grow. High humidity, regular rain and loose, humus-rich soil are also good conditions for growing yams.

The underground tubers reach a length of up to two meters and weigh up to 50 kg. They have a dark brown to black skin and are rich in provitamin A and potassium. Their taste is sweet and similar to that of chestnuts and sweet potatoes. In addition to the popular yams with white flesh, there are also varieties with purple and red flesh.

If handled carefully (no injuries or pressure damage to the tubers) and stored in an airy place, yam varieties can be kept for months. They play a considerable role in local and regional trade. However, the majority of yams are grown for home consumption.

Yams around the world

The plant originally comes from West Africa. There is evidence that wild forms of the yam were eaten here as early as 50,000 BC. It was domesticated in parallel in two independent places: In West Africa and Southeast Asia. Various theories assume that the first domestications took place between 3,000 and 5,000 BCE.

The exact processes by which the yam found its way from West Africa to Asia are not known. Various aspects such as trade, plant migration and local domestication processes established the yam in different regions of Asia. In South America, however, other types of yam played a role: here, indigenous populations used wild forms. The West African yam only reached the continent through the slave trade and colonialism in the 16th to 19th centuries.

Today, the yam is cultivated and eaten in many regions. Currently (2023), Nigeria, the Ivory Coast and Ghana are the countries with the largest yam cultivation areas worldwide.

A staple food

They are an important source of starch in the kitchens of the tropics. Almost all types of yam are toxic when eaten raw due to their alkaloid content. The bitter substance, the poisonous alkaloid dioscorin, is broken down during cooking.

In the African tropics in particular, yam tubers are one of the most important staple foods for the population and are boiled, roasted, baked or eaten as porridge. As with manioc, ‘fufu’ is also prepared from yam tubers in West Africa. In addition to fresh consumption, the production of dried foods (dried flakes = gari, flour, starch) plays a subordinate role for yams.

Prepared as chips or puree, yams make a nutritious side dish. Yams can also be used to make delicious soups and stews – which often include the leaves of the yam plant. A casserole with other vegetables also tastes good. Because of its starch content, yams are very filling.

Traditional medicinal plant

In Asia and on the American continent, the tuber is said to have a rejuvenating effect. The indigenous population of America also knew that certain foods could be used medicinally. It is used to address many different symptoms:

• The yam root can alleviate rheumatic complaints, biliary colic and gastrointestinal cramps and is therefore used for this purpose in various regions of the world.
• Indigenous women used the yam root for contraception and as a painkiller during labor. In modern medicine, secondary metabolites, including diosgenin, from the yam tubers were used to synthesize steroids for the production of the first birth control pills.
• At the same time, yam products are used to treat infertility and impotence. Impotence is treated with yams, particularly on some Japanese islands.
• The bitter yam is used to treat diabetes, as it has a blood sugar-lowering effect.
• Today, wild yam is also used in hormone therapy to alleviate menopausal symptoms.
• The Chinese yam, also known as ‘light root’, is used in anthroposophic medicine.

Sources

S. Rehm, G. Espig, 1984: Die Kulturpflanzen der Tropen und Subtropen
W. Franke, 1992: Nutzpflanzen der Tropen und Subtropen
Eti-Ebong et al. 2023: Indigenous Food Yam Cultivation and Livelihood Practices in Cross River State, Nigeria. Link.
Wikifarmer. Tulisha Malichi: Yam: History, uses, and plant information. Link.
Pflanzenforschung.de: Yams. Link.
Applied Worldwide Nigeria: Yam Festival in Nigeria: its Importance and Celebration. Link.
Menopause Center: Relaxed through the menopause with the yam root. Link.
Anthrowiki: Light root (Dioscorea batatas). Link.