Storage is the act of preserving commodities in a safe place for future use. Agricultural produce is preserved over a certain period to serve as a continuous source of food materials, seed, merchandise, or strategic stock.
The duration of storage is determined by economic, social, and structural features of the specific postharvest system.
Storage, a critical postharvest operation, relies on structures varying in shape, capacity, construction materials, durability, cost, and effectiveness.
A wide range of plant and animal products, including dried and smoked fish, meat, hides and skin, timber products, and household goods such as clothes, carpets, tea, and cocoa, are preserved for varying periods.
Crop products, forming the staple diets in most parts of the world, constitute the major class of stored agricultural commodities. These are grouped into durables, semi-durables, and perishables.
Durables, such as grains from cereals and pulses/grain legumes (e.g., rice, maize, sorghum, millet, wheat, groundnut, beans, soybeans, cowpeas, Bambara groundnut), can be stored for months or years.
Semi-durables, including roots and tuber crops like cassava, yam, potato, and cocoyam, can only be stored for a short time and form the main energy source in the diets of most developing tropical countries, requiring specialized storage structures.
Perishables, such as fruits and vegetables (e.g., oranges, mango, cashew, pear, pawpaw, watermelon, tomato, onion, cabbage), have limited storage durations.
Storage structures generally possess features conducive to good preservation, often constructed with natural, locally available materials and relatively inexpensive.
Designs and capacities vary based on commodity type and harvest size. Storage structures are broadly classified into two types: ventilated and unventilated (hermetic) structures.
Root and tuber crops are also stored, though not for as long as grains and pulses.
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Storage Methods for Grains and Pulses in Agriculture
Storage structures for grains and pulses possess features conducive to effective preservation and are classified into ventilated and unventilated (hermetic) structures.
Common ventilated structures in tropical Africa include cribs and bags, featuring vents or small holes that provide ventilation to the stored commodity and any pests it may harbor.
At the small farming scale, grains are stored traditionally in various containers made from clay, thatch, mud, wood, or stones, which are cost-effective and environmentally suitable.
Larger granaries, designed for storing substantial quantities for extended periods, may use more permanent materials like metal silos or wooden granaries with iron sheet roofs.
Open storage structures, such as wooden platforms on stakes or posts, support crops in heaps or regular layers. Harvested crops may be hung on frames inside houses or tied as sheaves to tree branches outside.
A more protected system is the crib, a four-cornered wooden structure with ventilated sides covered with woven straw, grass stalks, or wire netting.
Closed granaries, varying in size and made from mud, woven straw, or a mixture of mud and chopped straw, may be four-cornered, spherical, or conical, with straw roofs and protective lids or resting on foundation stones.
Grains inside granaries are well-protected against rain and insect pests. Smaller grain quantities are stored in calabashes (gourds), clay pots, sacks, woven baskets, or jerrycans, facilitating frequent consumption.
Hermetically sealed jerrycans and jars with a stone on top deplete oxygen and increase carbon dioxide, eliminating insect pests.
Concrete or metal silos, holding 5–10 tons of grains, are used by medium- and large-scale farmers. Plastic sacks, bags, prefabricated iron halls, and flexible plastic silos are gaining popularity.
Large warehouses and metal silos, common among cooperatives and traders, can store over 3,000 tons of produce.
Plastic bags, ideal for preserving legumes and cereals due to their portability, are filled with grains and sealed hermetically, sometimes after dosing with fumigants like aluminum phosphide (Phostoxin) or pirimiphos methyl (Actellic EC or Dust). These fumigants pose hazards if mishandled.
A safer method, double or triple bagging, uses one or two layers of transparent polyethylene with the plastic sack, eliminating the need for fumigants.
Sacks are filled to three-quarters of their volume, sealed by twisting the neck and tying tightly, and stacked on platforms or wooden pallets to avoid moisture absorption. Bags are arranged in a criss-cross manner to prevent falling.
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Storage Techniques for Root and Tuber Crops
Root and tuber crops, classified as semi-durables, can only be stored briefly. Cassava tubers deteriorate rapidly within 3–4 days post-harvest, developing bluish discoloration around vascular bundles, known as vascular streaking, caused by enzymatic processes.
Streaking is prevented by dipping tubers in warm water (53°C for 45 minutes), storing under anaerobic conditions, submerging in water, or refrigerating.
Starch quality in tubers declines during storage. Cassava roots can be stored in boxes with moist sawdust for eight weeks after curing at 30–35°C and 80–85% relative humidity.
High cyanide or prussic acid content in most cassava cultivars necessitates elaborate processing before consumption.
Yam is stored in barns made of vertically arranged wooden poles, 3–4 meters high, with tubers tied longitudinally using twine. Barns, shaded and located in well-ventilated areas, prevent humidity buildup that favors rotting and overheating from respiratory activities.
Regular inspection identifies and removes rotting or sprouting tubers to prevent disease spread, especially after rain, which spreads inoculum from rotted tubers to neighboring ones, particularly those below. Shading, ventilation, and constant inspection are essential for effective yam storage.
Sweet and Irish potatoes are cured post-harvest to heal wounds and toughen the skin (periderm), minimizing microbial infection and enhancing resistance to handling damage.
Curing occurs for 4–5 days under ambient conditions, followed by storage at 13–16°C and 85–90% relative humidity. Sweet potatoes are often stored in underground pits lined and covered with dry grass, on platforms, or in baskets.
Leaving tubers in the ground until needed increases vulnerability to weevil attacks. Ascorbic acid content decreases during storage.
Storage Practices for Perishable Fruits and Vegetables
Fruits and vegetables, classified as perishables, cannot be stored naturally for long. Low temperatures or ventilated containers are optimal for storage.
Fruits like mango, oranges, pawpaw, and guava should be harvested at physiological maturity or half-ripe, completing ripening in storage or transit.
They are transported in ventilated structures like perforated cartons, jute woven bags, or open vans. Vegetables like tomatoes, harvested half-ripe, are transported in woven baskets or under refrigeration.
Onions can be stored for 3–4 months when spread thinly on floors lined with dry sand or grass, after curing by sun- or shade-drying for 3–4 days. Stored onions require ventilation and periodic inspection to remove rotting or sprouting bulbs.
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