Storage
Roots and tubers such as yam are living organisms. When stored, they continue to respire. The respiration process results in the oxidation of the starch (a polymer of glucose) contained in the cells of the tuber, which converts it into water, carbon dioxide and heat energy. During this transformation of the starch the dry matter of the tuber is reduced.
Amongst the major roots and tubers, properly stored yam is considered to be the least perishable. Successful storage of yams requires:
- initial selection of sound and healthy yams;
- proper curing, if possible combined with fungicide treatment;
- adequate ventilation to remove the heat generated by respiration of the tubers;
- regular inspection during storage and removal of rotting tubers and any sprouts that develop and;
- protection from direct sunlight and rain.
Storing yam at low temperature reduces the respiration rates. However, temperatures below 12°C (53.6°F) cause damage through chilling, causing a breakdown of internal tissues, increasing water loss and yam's susceptibility to decay. The symptoms of chilling injury are not always obvious when the tubers are still in cold storage. The injury becomes noticeable as soon as the tubers are restored to ambient temperatures.
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.
Sprouting rapidly increases a tuber's respiration rates, and accelerates the rate at which its food value decreases.
Certain cultivars of yam store better than others. The easier to store yams are those that are adapted to arid climate, where they tend to stay in dormant low-respiration stage for much longer than yam breeds that are adapted to humid tropical lands where they do not need dormancy. Yellow yam and cush-cush yam, by nature, have much shorter dormancy periods than water yam, white yam or lesser yam.
Storage losses for yams are very high in Africa, with insects alone causing over 25 percent harvest loss within 4 months.
Read more about this topic: Yam (vegetable)
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