Homepage → Sustainable Storage Technologies → Hermetic Storage of Dry Grains and Other Durable Agricultural Products → Historical Storage
Historical Storage
Underground Pits
Underground pits
The considerable literature on sealed storage of grain termed "air-tight storage" or "hermetic storage" is well summarised by Hyde et al. (1973), and De Lima (1990). From this a clear picture emerges of underground storage in pits, from pre-historic times until the present day as a traditional method that is frequently sufficiently air-tight to enable insects and other aerobic organisms in the grain-mass to reduce oxygen (O₂) concentrations below those permitting insect development. These pits were excavated into the soil or rock, and are sometimes lined with supporting walls of brick or cement. However, the ideal situation of O₂ depletion and carbon dioxide (CO₂) accumulation as demonstrated in laboratory experiments of Oxley and Wickenden (1963) is rarely achieved. This is generally because of gas-exchange through the pit walls and roof, and the sorption of CO₂ by the grain itself and sometimes by the pit walls (Hyde and Daubney, 1960).
Semi-underground structures
Large-scale construction for prolonged storage of grain surpluses in Argentina during the second world war consisted of below- and above-ground concrete lined trenches covered with flexible roofs (Anon., 1949). Later attempts at achieving hermetic storage were the Cyprus bins constructed in the 1950s (Hyde et al., 1973). These consisted of concrete lined conical pits surmounted by domed concrete-shell roofs. They were successfully used under hermetic conditions for a number of years. Improved versions of these structures were later constructed in Kenya for hermetic storage of the national grain reserve (De Lima, 1990).
Small-Scale Structures
Above-ground small-scale structures
Another traditional method used by subsistence and small-scale farmers has been the storing of grain in sealed gourds, though these provide an incomplete hermetic seal unless treated with a sealing material (McFarlane, 1970). A related method adopted in a number of tropical countries has been the adaptation of empty oil-drums and other metal drums for storage (Pattinson, 1970; Sakho, 1971). To prevent development of heavy infestations before control is achieved, these metal drums should be completely filled. This is because when only partially filled, the headspace volume may remain large (in relation to the grain mass) and developing populations may cause perceptible damage before O₂ concentrations are sufficiently reduced to arrest development.
Underground Flexible Structures
Here the main approach to achieving lower levels of O₂ and higher accumulations of CO₂ has been by lining pits with plastic liners in order to improve the hermetic seal (Donahaye et al., 1967; Dunkel et al., 1987). With similar intent small scale underground storages have been developed for farmer storage of corn and dry beans in Brazil (Sartori and Costa, 1975; Sartori, 1987). Clearly this technology does not lend itself well to multiple usage.
