Storage of yam tubers and yam seeds

Introduction

Yam is the common name for some species in the genus Dioscorea (family – Dioscoreaceae). These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, – Latin American, the Caribbean and Oceania. There are many cultivars of yam.

Yam is a versatile vegetable. It can be barbecued; roasted; fried; grilled; boiled; baked; smoked and when grated it is processed into a desert recipe. Yams are a primary agricultural and culturally important commodity in West Africa where over 95 percent of worlds yam crop is harvested and 71 percent is been harvested from Nigeria. Some varieties of these tubers can be stored up to six months without refrigeration, which makes them a valuable resource for the yearly period of food scarcity at the beginning of the wet season.

Yam tubers can grow up to 1.5metre (4.9 feet) in length and weigh up to 70 kilogram (1541b) and 3 to 6 inches high. The vegetable has a rough skin which is difficult to peel, but which softens after heating. The skin vary in colour from dark brown to light pink. The majority of the vegetable is composed of a much softer substance known as the “meat”. This substance ranges in colour from white or yellow to purple or pink in mature yams.

Due to their abundance and importance to survival, the yam was highly regarded in Nigerian ceremonial culture and is part of many West African ceremonies.

Definition and importance of yam tuber

They are monocots, related to lilies and grasses. Native to Africa and Asia. Yams vary in size from that of a small potato to over 60 kilograms. There are over 600 varieties of yams and 95 percent of these crops are grown in Africa while 71% were from Nigeria.

Importance of yam tuber

Yam tubers are important to man in the following ways:-

  • For consumption
  • High cultural value
  • Source of carbohydrates
  • Major source of income (food export)
  • Provision of job employment
  • Used in industry

Reasons for storing yam tubers & seedling

  • To have enough to eat throughout the year
  • To prevent it from spoilage
  • To make available good seeds to farmers during farming season
  • To encourage farmers to grow more yams
  • To supply food to food industries all the year round
  • To see that it is available during difficult periods
  • To regulates the prices of yam tubers

Causes of yam spoilage

  • Physical injuries (improper harvestry)
  • High moisture
  • Insect pest
  • Rodent
  • Excessive Heat
  • Germs & Diseases (Micro-organism)

Signs of yam spoilage

  • Softening of the tuber (yam rot)
  • Sprouting (break of dormancy)
  • Hard and bitter taste
  • Internal discolouration
  • Presence of insect
  • Mouldiness
  • Shriveling

Curing of yam tuber

  • Field curing
  • Curing with heated air
  • Bulk system for curing onions
  • Emergency curing

Curing root and tuber crops such as sweet potatoes, potatoes, cassava and yam is an important practice if these crops are to be stored for any length of time. It is accomplished by holding the produce at high temperature and high relative humidity for several days while harvesting wounds heal and a new protective layer of cells form.

While curing can be initially costly, the long extension of storage life makes the practice economically worthwhile.

Temp0   R.N Days
C F %  

1 – 4

32 – 400 90 – 104 90 – 100

Field curing: Yams and other tropical root and tuber crops can be cured out-doors if pilled in a partially shaded area cut grasses or straw can be used as insulating materials and the pile should be covered with canvas, burlap or woven grass materials. Curing requires high temp0 and high relative humidity, and this covering will trap self-generated heat and moisture. The stock should be left for about four (4) days.

Storage methods for yam tubers

–           Delay harvest occasionally

–           Burying underground after harvest

–           Yam Barn (Storage structure for yam tubers) yellowish kkkk for storage

Yam barn

–           Clean the tubers before storage

–           Tie tubers one-by-one to erect poles using long pieces of fibres looped round each am and pulled tight.

–           Place each row of poles 2 metres apart so that a “yam barn” may occupy a considerable area.

–           This system enables the farmers to inspect each yam daily and remove any sprouts or rotting tuber as soon as they appear.

–           Construct a roof of palm or grass thatch to keep out rain and sun

Improved yam barns

–           NSPRI has improved the technique of storing yam in barns

–           A ventilated shed has been designed, constructed and tested for yam storage

–           In the improved yam barn, the unbrushed and undamaged tubers are arranged on slatted flat forms or shelves in such a way that the sprouting ends can be reached very easily.

–           Sprouts are manually removed from the yam as soon as they are detected.

–           NSPRI has been able to store yams with less than 5% spoilage for 5 – 6 months by this method.

Design and construction of a ventilated yam barn

An improved yam barn comprises a number of yam shelves sheltered by a yam shed the yam shed is constructed in the following steps.

–           Choose a well drained site with free air movement.

–           Mapping out the rectangular base of dimensions 480cm x 360cm and mark the position of the roof supporting poles alone by the sides.

–           Dig a hole of 120cm diameter and 30cm deep on sports for pole locations.

–           Treat all sawn woods for shed construction with wood preservatives (e.g solighum).

–           Erect vertical poles of 75m x 100mm sawn woods in the holes being 210cm above ground level and 30cm below.

–           Construct a double pitch thatch roof on the stand poles with a horizontal over-hang of at least 60cm.

–           Excavate a wall of cement block to a height of 60cm (3 layers of blocks) leaving out a door space on a shorter side.

–           On the wall space, construct a double hinged door of wood of wall dimension 180cm x 90cm

–           Fix a wall of wire netting round the side of the shed above the low solid walls.

–           Round the shed flow with sand crete

–           Build yam shelves of wood inside the shed.

 Yam processing products

–           Yam chips

–           Yam flour

–           Pounded yam

–           Drying

–           Frying

–           Roasting

–           Boiled e.t.c.

Storage methods for yam chip & flour

–           Use bruised fresh yam tubers that will not be consumed immediately.

–           Dry the processed yam slices to a moisture content of 15% or less. Using moisture meter.

–           Usually, newly produced yam chips are not infested.

–           Package the chips in polythene lined sacks for easy fumigation.

–           Bulk fumigation could be done when the yam chips have been stacked.

–           Protect the dried yam from re-wetting by rain or water.

–           Store on flat form in a store for about 6 months.

–           Keep away rats from the store by the use of trap.

Recommended storage practice for yams and products

–           Harvest mature yam

–           Avoid mechanical damage

–           Store only wholesome tuber

–           Allow yam to cure

–           Store in an improved yam barn

–           Process into yam chips, pounded yam using well cured yam.

–           Damaged yam can also be processed into yam chips, yam flour and pounded yam.

–           Processed products can be stored in airtight containers, bags and in stores.

–           Bagged yam chips can be disinfected using fumigants.

Conclusion

The role of a ventilated yam barn cannot be over emphasized in storage of yam tubers and seeds. Because of its economic importance and other reasons stated above. Yam is an annual crop so the need to store it is very important and ventilated yam barn is the best storage structure for storing yam tubers.

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