If the central store operator rejects a load because of excess moisture, do not load this grain into a sealed store where there is no escape for the moisture. In a sealed silo, there is no free venting and therefore no escape for moisture in the headspace. Grain must be stored below 12 per cent moisture content. Even grain loaded into an unsealed store must have less than 12 per cent moisture content as moisture can still migrate and condense in the upper layers and there will be some venting of moisture to the atmosphere. This area of the grain is at high risk from insect colonisation.
Grain is a living organism and releases moisture as it respires.
This is carried upwards in a silo by convection currents of air. These air currents are created by the temperature difference between the warm grain in the centre of the silo and cool silo walls, or vice versa. When grain is stored at less than 12 per cent moisture and is free of insects, the moisture increase in the upper layers of the grain will not be significant. If it is stored at above 12 per cent moisture content, enough moisture may be carried into the upper layers to place the grain at risk of going mouldy. Insect activity releases moisture and heat into the spaces between the grains.