Yams: there are many edible varieties from all over the world but most of them are grown in Africa, Papua New Guinea, South East Asia, West Indies, China, Japan, Korea, Thailand, India and even Australia. Yams which are grown uncultivated are highly poisonous (dioscorine) and a good way (the safest way) to test this is to cook the yam and feed it to the chooks and see what happens, as one cup of flesh of the wrong species can kill a person if eaten. Some varieties can loose this poison by washing and cooking it. In Mexico some species of yam are used for oral contraceptive production: it contains steroidal sapogenins (mostly diosgenin).
Yams grow in rich deep loam in lower parts of gullies, mounded up and planted beside posts, bamboo poles done as a tripod or against trees no closer than 1.5m apart, as this is a herbaceous climber. The direction of the growth of the vine as it climbs helps determine the variety of the yam. The leaves and hairy or prickly rootlets also help identify the yam. Cultivation of yams is declining and being taken over by Cassava, Sweet Potato and Taro which have a better taste and are much easier to grow.
Yams are usually planted from mature cuttings of the stem that will produce roots, and planted during dry weather with plenty of manure. The vine grows for about 9 to 10 months and when the leaves die back to the ground, the tuber is ready to dig up and this is usually a big job. I planted mine in the top of waxed boxes stacked 4-5 high and cut open when mature to reveal the tuber, but some species are too large for this method. Yams vary in size from 1 kg to 30 kg in weight and from purple to white in colour and they keep for months if kept in a cool place.
Yams are cooked whole in the skin or peeled and cut (covered with water to prevent browning) before cooking. Yams contain 1.2 % protein, 0.1 % fat, 23 % carbohydrate, 15mg ascorbic acid, 0.5mg iron, 0.10 mg thiamine, 0.03 mg riboflavin, 0.5 mg niacin and 15 mg calcium.
DATE: August 1997
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