At the time of harvesting, proper moisture content ensures lowest possible chance of spoilage during storage. If harvested at little higher moisture content to reduce shattering losses (shattering losses-dropping of the grain from spikelet), drying should followed to bring the moisture of grain in ideal range before storing the grains.
According to some references, grains (wheat, rice, sorghum, corn, millet etc) and pulses (Beans, chickpeas, lentils etc) should contain less than 12% moisture and less than 10% moisture respectively for storage purpose.
High moisture content (more than 12%) in grain during storage results in seed damage as high moisture promotes diseases. In range of moisture content from 13.5 % to 23%, many fungal spores grow. At such storage conditions, food grains will spoil easily and become unfit for use.
One critical factor in successful grain storage is the ideal moisture content of the crop. High moisture content promotes fungal and insect infestation due to respiration and germination and susceptible to storage losses.
Other major factor in successful grain storage is temperature within stored grains. As grains are biologically active after harvest and respire during storage, this process releases heat, water vapours and carbon dioxide.
By reducing the temperature of the stored grains, rate of respiration can reduce and so increasing the storage life by reducing germination possibility. At reduced temperature, the metabolic rate of insects and fungi decreases and so chances of spoilage also reduces.
During storage, a damp or warm spot in grain bed causes increase in respiration rate. As we discussed above, respiration produces heat and moisture. This heat and moisture arises from damp and warm spot can spread in entire storage space by convection, promoting molds and bacteria, which again respire and generate more heat and moisture. It therefore becomes a self-generating process and causes stored grains to spoil quickly.
Moisture and temperature changes in stored grains due to air movement inside the storage. Moisture in stored grain migrates due to change in temperature during different season i.e. winter and summer. Moisture migration can occur in stored bin even though grains are stored at an optimum moisture level i.e. safe for store. Due to this moisture migration, stored grains can deteriorates at top of bin in winter season and at bottom of bin in summer season.
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