Sun drying

postharvest-sundryingSun drying is a traditional drying method for reducing the moisture content of paddy by spreading the grains under the sun. The solar radiation heats up the grains as well as the surrounding air and thus increases the rate of water evaporating from the grains.

It is the most common drying method in Asia because of its low cost compared to mechanical drying. It requires little investment and is environmentally friendly since it uses the sun as the heat source and therefore produces no CO2.

However, sun drying tends to be labor-intensive and has limited capacity. Temperature control is also difficult in this method and grains can easily be overheat causing cracked grains which leads to low milling quality. It is also not possible to sun dry at night or during rain.

Options for sun drying

The following are recommended options for sun drying:

  • Mat drying
    The paddy are placed on mats, nets, or plastic sheets (canvas) to dry. It is the most hygienic sun drying practice because grains become less contanimated with stones and other dirt. It also allows easy collection in case of rainfall. However, there is danger of re-wetting from soil moisture.

  • drying-traditional-pavementPavement drying
    Farmers, grain collectors, traders, and millers use drying pavements, which are usually specifically constructed for drying. This method can dry a high capacity of grains and can be partially mechanized by using wheel tractors.

Fact sheet: Sun drying