Various Drying Methods for Agricultural Products

Sun Drying Sun drying is one of the oldest and most traditional methods of drying crops and grains, relying on solar energy to remove moisture from the product.

Advantages of Sun Drying:

• No fuel or mechanical energy required.
• Simple operation.
• Maintains the viability, germination, and baking qualities of the product.
• Reduces microbial activity and insect/pest infestation.
• No pollution involved.
• Low capital investment.
• Relatively low operating costs.

Disadvantages of Sun Drying:

• Uncontrolled and non-uniform drying leads to sun checks (cracks in kernels).
• Dependent on weather conditions; not possible in rainy or cloudy conditions.
• Cannot be done 24/7 or year-round.
• Losses due to shattering, birds, rodents, etc., typically range from 0.1% to 0.4%.
• Requires specially constructed large drying floors.
• The process can be unhygienic.
• Labor-intensive, requiring a large number of unskilled laborers.
• Not suitable for handling large quantities of grain in a short period.

2. Mechanical Drying Mechanical drying uses mechanical means to circulate heated air through the grain to remove moisture. It does not rely on natural sources like the sun.

Features of Mechanical Drying:

• The rate of drying is controllable by adjusting the temperature and humidity of the hot air, which can improve milling quality and reduce grain cracks.
• Can be done independently of weather, both day and night.
• Automatic processes with minimal skilled labor, except for a trained operator.
• No losses due to birds, rodents, or insects.
• The entire process is hygienic.
• Can operate round the clock and throughout the year.
• Suitable for handling large quantities of grain in a short time after harvest.
• Requires minimal space for operation.

Disadvantages of Mechanical Drying: Fuel, electricity, or mechanical power is required to operate the system, making it more expensive than sun drying. Commercial drying costs are higher.

3. Types of Mechanical Dryers Mechanical dryers can be classified into three main types based on the drying mechanism:

• Contact Drying (Conduction Drying): In this process, heat is transferred from a solid surface (usually metallic) to the wet material mainly by conduction. The drying occurs as moisture is transferred through direct contact with the heated surface. Used in smaller-scale drying applications.
• Convection Drying: Hot gases (drying agents) come into contact with the wet material, supplying heat and carrying away the vaporized moisture through convection. More popular in grain drying systems. Higher fuel consumption per kg of moisture evaporated compared to contact drying, due to energy losses in air movement.
• Radiation Drying: Based on the absorption of radiant energy (from the sun or other radiant heat sources), which is transformed into heat energy by the material. Sun drying is an example of this method. Less energy-efficient than convection or contact drying but still widely used for small-scale, traditional drying practices.