Sun Drying

Drying occurs as warm, relatively dry air passes over the produce and carries away evaporated moisture. In open-sun drying the crop is exposed directly to sunlight and wind; in a solar dryer, the sun heats air that is then drawn through or over the produce, often within a transparent or dark enclosure that raises the temperature and speeds drying while keeping out rain, dust, and pests. Turning or stirring the crop helps it dry evenly.

The aim is the same as for any drying: to reach a moisture content low enough that moulds and insects cannot thrive in storage. Grain dried in the sun still needs to reach a safe storage moisture, and its dryness should be checked rather than assumed.

• Weather dependence: rain and cloud can interrupt drying and re-wet the crop, encouraging mould.
• Contamination: crop dried on bare ground can pick up soil, stones, dust, animal droppings, and pests.
• Uneven and incomplete drying, which leaves pockets of moist grain that spoil in storage.
• Re-wetting overnight from dew or humidity if the crop is not gathered and protected.

• Dry on clean mats, tarpaulins, or raised drying floors rather than on bare ground.
• Spread produce in thin layers and turn it regularly for even, faster drying.
• Gather and cover the crop before rain and overnight to prevent re-wetting.
• Check moisture before storage and finish drying if the crop is still too moist.
• Consider a solar dryer where cleaner, faster, and weather-protected drying is needed.