Drying
[画像:postharvest-drying-manual-2]Drying reduces grain moisture content to a safe level for storage. It is the most critical operation after harvesting a rice crop.
When rice is harvested, it will contain up to 25% moisture. High moisture level during storage can lead to grain discoloration, encourage development of molds, and increase the likelihood of attack from pests. It can also decrease the germination rate of the rice seed.
drying-systems-diagram Click to zoom
It is important to dry rice grain as soon as possible after harvesting— ideally within 24 hours. Delays in drying, incomplete drying or ineffective drying will reduce grain quality and result in losses.
Paddy drying methods include traditional and mechanical systems with varying technological complexity and capacities for either farm or commercial level.
Traditional drying systems
Traditional drying systems are still practiced in many areas because of its low cost and ease of management. These include methods, such as:
- Sun drying - spreading grains under the sun, on mats and pavements
- Mat drying - used in small to medium-scale drying where threshed grain are placed on mats, nets, or canvas
- Pavement drying - often used in large-scale drying for grain collectors and millers, where grains are laid on pavements specifically made for drying
- Field drying and stacking - a method for pre-drying hand-harvested crops before threshing where farmers cut rice panicles in the field and stacked them in small piles on top of the crop stubble
Although field drying and stacking is still practiced in some areas, it is not recommended because it can lead to high losses when grains become overdried and shattered.
Drying systems
Drying can be done using either traditional or mechanical drying systems.
Drying basics
Since drying practices can have a big impact on grain quality or seed quality, it is important to understand some fundamentals of grain drying.
Drying strategies
When developing a drying strategy, it is important to consider other activities in rice post production system, and look into the economic criteria
The Solar Bubble Dryer
Solar drying is the latest in drying technology. In this method, sun drying is simulated using a solar bubble dryer which protects the grains despite changes in weather patterns and thus, prevents postharvest losses.
In-store drying
In in-store drying, the drying process continous until it reaches the equilibrium moisture content; thus, over drying of the bottom layer is minimized.
Sun drying
Sun drying is a traditional drying method for reducing the moisture content of paddy by spreading the grains under the sun.
Economic aspects of drying
A guide to site-specific assessment on the potential of mechanical drying
Measuring moisture content
Different moisture contents are required per postproduction operation. These should be followed to ensure good quality of paddy.
Heated air drying
Heated air drying allows for suitable drying air conditions to be set. In this method, drying can be carried out any time of the day or night.