Yam plants have thick tubers (generally a development of the base of the stem) which often have thick, almost barklike skin. The long, slender, annual, climbing stems bear lobed or entire leaves that are either alternate or opposite. The unisexual flowers are borne in long clusters. The flowers are generally small and individually inconspicuous though collectively showy. Each consists of a greenish bell-shaped or flat perianth of six pieces, enclosing six or fewer stamens in the male flowers and surmounting a three-celled three-winged ovary in the female flowers. The ovary ripens into a membranous capsule, bursting by three valves to liberate numerous flattish or globose seeds.
Yam tubers consist of about 21% dietary fibre and are rich in carbohydrates, vitamin C and essential minerals.
The tuber is the main part of the yam plant which has high carbohydrate content (low in fat and protein) and provides a good source of energy. Unpeeled yam has vitamin C. Yam, sweet in flavour, is consumed as boiled yam (as cooked vegetable) or fufu or fried in oil and then consumed. It is often pounded into a thick paste after boiling and is consumed with soup. It is also processed into flour for use in the preparation of the paste. Its medicinal use as a heart stimulant is attributed to its chemical composition, which consists of alkaloids of saponin and sapogenin. Its use as an industrial starch has also been established as the quality of some of the species is able to provide as much starch as in cereals.
Storage of Yam Tuber
Roots and tubers such as yam are living organisms. When stored, they continue to respire. To reduce post-harvest losses during storage, the reduced temperature in storage facilities should be maintained. The best temperature to store yams is between 14-16°C (57.2-60.8°F), with high technology controlled humidity and climatic conditions, after a process of curing. Most countries that grow yam as food staple are too poor to afford high technology storage systems.
There are several traditional storage structures used for yam storage including leaving the tubers in the ground until required, the yam barn, and underground structures. Leaving the tubers in the ground until required is the simplest storage technique practised by rural small-scale farmers. When carried out on-farm, this type of storage prevents the use of the farmland for further cropping. Harvested yams can also be put in ashes and covered with soil, with or without grass mulch until required.
The yam barn is the principal traditional yam storage structures in the major producing areas. Barns are usually located in a shaded area and constructed so as to facilitate adequate ventilation while protecting tubers from flooding and insect attack. Barns consist of a vertical wooden framework to which the tubers are individually attached