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If grain moisture content is too high, even the best aeration equipment and monitoring management will not keep the grain from spoiling. All stored product insect pests, micro-organisms, including molds, require moisture to survive and multiply. If the moisture content in a product going in to store is too low, insects and micro-organisms will be unable to grow provided that the moisture in the store is also kept low.
This moisture content is referred to as the safe moisture content Due to excessive humidity, multiplication of fungi particularly Aspergillus spp., which produce dangerous toxins (Aflatoxins), will make grain unfit for human consumption. Wet heating: increase in the grain temperature due to the activity of fungus in presence of high moisture.Dry heating: increase in the temperature due to the activity of insects and their respiration.Equilibrium moisture content: it is the point at which the grain not loose nor gain the moisture from surrounding air. Safe moisture content levels for cereals and pulses stored below 270c
Product Safe moisture content (%) Cereals: maize flour 11.5 Maize shelled 13.5 Millet 16.0 Rice (milled) 13.0 Rice 15.0 Sorghum 13.5 Wheat 13.5 Wheat flour 12.0 Pulses: broad bean, cow pea 15.0 Lentil, pea 14.0
Moisture content in foodgrains storage:
Produce contains moisture which is present in grain in two main forms, water of composition and absorbed water or free water. However, the quantity of free water held by the grain product is a critical factor which place a vital role in safe storage of food grains. It has been defined by IS as loss in weight brought about by heating for two hours at 130 to 133 0c. In another definition, It has been defined as amount of water that can be removed without changing the chemical structure of grain.
The amount of water in dry foodgrains varies from about 0.05kg/kg to 0.30kg/kg. The activities of biotic factors are also governed by the moisture content of stored products. Besides the rate at which chemical and physical changes take place, increase very rapidly with increase in the moisture content of the grain. The more important factor is that at low moisture content, the grain and their products can be stored for longer period safely.