Onions are a staple in global cuisine and a vital crop in agriculture. Their post-harvest handling and storage significantly impact quality, shelf life, and market value. Proper techniques can mitigate losses, improve profitability for farmers, and ensure year-round availability for consumers. This blog explores the best practices for curing, grading, packaging, handling, and storing onions, ensuring minimal post-harvest losses and maintaining quality.

The Importance of Curing

Curing is the primary post-harvest treatment required for long-term onion storage.
This process involves drying the necks and outer scale leaves of onion bulbs to prevent moisture loss and decay.

Key Steps in Curing

1. Drying the Neck and Outer Layers: This ensures the necks are tight and the outer scales rustle, reducing the risk of rot.
2. Weight Loss: Proper curing results in a weight loss of 3-5%, which is acceptable for storage.
3. Curing Methods:
   • Field drying in warm, well-ventilated conditions.
   • Artificial heat in damp climates, using ducts at a temperature of 30°C.
   • Shade curing by hanging bulbs in bunches, which improves bulb color and reduces storage losses.

Grading for Market Readiness

After curing, onions are graded to ensure uniformity in size, shape, and quality. Grading enhances market value and reduces storage losses.

Grading Categories

• Extra Large Onions (>6 cm diameter)
• Medium Onions (4-6 cm diameter)
• Small Onions (2-4 cm diameter)

Grading also removes defective bulbs, such as those with thick necks, bolted stems, or signs of decay. Export-grade onions must meet stringent standards, including tolerance limits for size and defects.

Packaging for Transportation and Storage

Proper packaging ensures safe transportation and minimizes post-harvest losses.

Best Practices in Packaging:

1. Use open-mesh jute bags (40 kg capacity) for domestic markets.
2. For export, pack onions in 5-25 kg open-mesh bags or 14-15 kg wooden baskets (for specialty varieties like Bangalore Rose).
3. Nylon net bags are highly recommended for reducing storage losses due to better ventilation.

Handling Onions with Care

Handling practices play a crucial role in maintaining onion quality during storage and transit.

Key Recommendations

• Avoid dropping onions from heights greater than 6 feet.
• Stack onions in layers no higher than 2.5 meters to prevent bruising and rot.
• Use wooden crates instead of gunny bags for better aeration.

Storage Techniques for Longevity

Storage is critical for extending the shelf life of onions, especially for consumption and seed production.

Factors Affecting Storage

• Temperature:
  • Sprouting increases at 10-25°C.
  • Weight loss is higher at temperatures above 35°C.
• Relative Humidity (RH): Higher RH promotes rooting.

Storage Conditions

1. Ambient Conditions: Onions are best stored at 27-30°C with 60-65% RH.
2. Cold Storage: Maintain 0-2°C and 60-75% RH to minimize losses, but beware of sprouting once onions are removed.

Chemical Treatments

• Apply Maleic Hydrazide (2500 ppm) 75-90 days after transplanting to control sprouting.
• Use 0.1% Carbendazim sprays post-harvest to prevent storage rots.

Improved Storage Structures

Traditional storage methods often result in high losses. Improved storage structures are essential for reducing moisture, heat, and pest-related damages.

Features of Improved Storage Structures

1. Raised Platforms: Minimize moisture and dampness.
2. Ventilation: Bottom and side ventilation prevents the formation of hot, humid pockets.
3. Roof Design: Use materials like Mangalore tiles to reduce heat buildup.
4. Stack Dimensions: Limit stack width to 60-120 cm and height to 100-120 cm, depending on onion type and weather conditions.
5. Cubicle Arrangement: Allow space between stacks for better airflow.

These structures can store up to 750 kg of onions per cubic meter and are ideal for maintaining quality over extended periods.

Efficient Transportation

Efficient transport is critical for minimizing damage during transit. Onions are commonly transported using:

• Bullock carts, tractor trolleys, and trucks for domestic distribution.
• Ventilated ships, motorboats, and containers for export to Gulf and Southeast Asian countries.

Conclusion

Mastering post-harvest technology is essential for the onion industry to thrive. From curing and grading to advanced storage solutions, every step plays a vital role in reducing losses and ensuring high-quality onions reach markets. By adopting improved storage structures and handling practices, farmers can enhance their profitability while consumers benefit from stable prices and consistent supply.

Key Takeaways

1. Curing and grading are vital for preparing onions for storage and marketing.
2. Improved storage structures can significantly reduce losses compared to traditional methods.
3. Proper packaging, handling, and transportation ensure minimal damage during distribution.

Investing in these practices will create a sustainable onion supply chain, benefiting all stakeholders involved.