Post-Harvest Losses in Grain Storage

Grain storage and handling is the process whereby grain is received, processed, stored, and shipped off. Grain storage is an early step in the food value chain, acting as facilitator between producers and feeders/ processors by providing safe and secure storage of grain. Facilities for grain storage and handling must be adequate to ensure that no component of the grains are depleted.

Post-harvest losses of cereal grains during storage account for 1-2% in well managed systems and 20-30% in poorly managed systems. During harvest, the moisture content of grain is around 20-30%, and harvest temperature is 25-50˚C depending on the growing region of the world. This harvested moist and warm grain should be dried and cooled before storage. Moisture content and temperature are the main factors that determine the length of storage time for storing grains without spoilage.

Insects and moulds are the main predators during storage of grains and growth of these insects and micro-organisms increases dramatically when the relative humidity inside the grain bins rise above 70% and temperature is above 25˚C. Prevention of insect and mould growth is a better option than the control measures, and if insect and mould growth couldn’t be controlled at an early stage, there is the potential for total damage of the grain.

The safe storage time of grains decreases with increase in storage temperature and moisture content of grains. Temperature gradients inside the grain bin lead to moisture migration and when moisture from warmer areas migrate to colder areas condensation could occur in cool grain near the top of the bin or on bin ceiling or wall due to moist warm air coming in contact with the cool surfaces. If the ventilation of bin is poor, the moist and warm air cannot be removed from the bin and can create favourable conditions for insect and mould growth.

Depot managers should regularly inspect the product; especially product received with a high moisture content must be closely monitored. In moist product insects multiply much faster than in dry product. Furthermore, depot managers should also be on the lookout for leaks in silo bins/-bags and bunkers that could cause spots to become wet, mouldy and with insects. The trend is often to discard small quantities of wet grain, but it is this product that serve as a breeding ground for insects.

Depot managers should be particularly weary of infestations by insects that develop inside the product, such as weevils and the Angoumois grain moth. By the time you are able to notice live adult insects in the product, it may be already too late as it may have caused considerable damage to the product already.

One of the most dangerous sources of contamination of clean product, is small quantities of the product that is periodically delivered by retailers or agents at the depot for storage. This product is almost invariably heavily contaminated with insects and the later it is delivered after the intake of the crop, the more severe the contamination.

There is no specific percentage for storage loss, but the declared loss should be within acceptable levels based on established local conditions. Factors which largely contribute to storage loss are grain shrinkage and insect infestation. Shrinkage refers to loss in volume in weight of grain placed in the bin and the loss is basically due to moisture reduction and respiration leading to dry matter loss.