Good storage practices for grains and seeds (cereals, pulses and oilseeds) aim to maintain the quality of the harvested product for as long as possible, by acting on the factors and mechanisms that alter quality.
Quality deterioration depends on four major factors:
- grain moisture (water content) ;
- temperature during storage;
- the presence of insects;
- storage time (figure 1).
The first factor, the moisture content of the grain, conditions the development of storage molds (microscopic fungi of the Penicillium or Aspergillus genera). It is therefore imperative that the grain to be stored for several months be perfectly dry. If it is not dry at the time of harvest, or if it contains too many moist impurities (often the case with oilseed crops), it should be dried and, if necessary, the moist impurities separated before long-term storage.
The second factor, grain temperature, conditions the rate of multiplication of harmful insects after harvest: weevils, silversides, capuchin beetles, Tribolium, as well as the rate of mold proliferation, a source of heating in damp grains. Storage at temperatures above 20°C over a long period of time reduces vigor and germination capacity, which is not acceptable for malting barley or seed.
The third risk factor to control is the presence of insects that attack legume seeds (before harvest) or cereals during the storage period.
In the case of cereals (wheat, barley, rye, triticale, naked oats, brown rice (hulled), maize, sorghum, etc.), these insects do not come from the field, but are permanently present in small colonies in grain handling equipment and circuits. The insects that attack cereals after harvest are adapted to living inside the grain mass and in dead spots in circuits (augers, conveyors, elevators, etc., Figure 2) that are inaccessible to cleaning.
The fourth risk factor is long-term storage (one year or more). When the storage period exceeds 6 months, this favors :
- the multiplication of micro-organisms in areas of the stock that have regained moisture (especially in square-section metal cells or flat storage bins)
- the multiplication of insect pests when grain temperatures exceed 13-14°C
- natural aging of the grain.