05/10/2025

Shipping Onions

Ventilation and Odor Tips

Fresh onions packed in cardboard boxes prepared for shipping.

Onions are a staple in kitchens worldwide, but shipping them requires meticulous attention to detail to ensure they arrive in optimal condition. Proper ventilation, temperature and humidity control, sprouting prevention, and odor management are essential to maintain their quality during transit. This article provides a comprehensive guide to the best practices for shipping onions, incorporating advanced technologies and lesser-known insights to enhance efficiency and reduce spoilage.

Understanding Onion Physiology

Onions are bulb vegetables with high water content (82-88%) and are sensitive to environmental conditions. They respire, releasing heat, carbon dioxide (CO2), and water vapor, which can lead to self-heating if not properly managed. Onions are also sensitive to ethylene gas, a ripening agent produced by fruits like apples and pears, which can accelerate sprouting. Maintaining a cool, dry, and dark environment with adequate air circulation is crucial to preserve their firmness, flavor, and nutritional value.

Ventilation Requirements

Adequate ventilation is critical to prevent moisture buildup, which can cause mold, decay, and self-heating. Onions' respiration process generates heat and CO2, and without proper airflow, this can create a cycle of spoilage. Key ventilation practices include:

Breathable Packaging: Use wide-meshed jute fabric or plastic bags, crates, boxes, or cartons to allow air circulation. Avoid small-meshed bags, as they have low air permeability and can trap moisture.
Container Ventilation: Ensure shipping containers have sufficient vents to promote airflow. For refrigerated containers, maintain a ventilation rate of 60-80 air circulations per hour with a continuous fresh air supply. For general cargo, a rate of 25 air circulations per hour with constant fresh air is recommended.
Light Protection: Protect onions from light during ventilation to prevent sprouting, as exposure to light can trigger growth.
CO2 Monitoring: Keep CO2 levels below 0.5 vol.% to avoid fermentation and rotting due to inadequate oxygen levels.

These practices reduce the risk of spoilage and ensure onions remain fresh during transit.

Temperature and Humidity Control

Maintaining precise temperature and humidity levels is essential to prevent physiological damage to onions. The following guidelines are recommended:

Temperature: Ship onions at 32-40°F (0-4°C) to maintain quality, with 32-36°F (0-2°C) preferred for extended periods. The maximum admissible temperature is 86°F (30°C), as temperatures above 104°F (40°C) can cause "scalding" (physiological heat injury), leading to rot, spoilage, sprouting, and self-heating. Onions can withstand gentle freezing to 27°F (-3°C), but this should be avoided, as frozen onions are prone to bruising and rotting when thawed.
Humidity: Maintain relative humidity at 75-80% when shipping at 32-40°F (0-4°C). If shipping at higher temperatures, such as 59°F (15°C), reduce humidity to 65-70%. Keeping the outermost scale leaves dry prevents rot, root growth, and sprouting.
Pre-Transport Preparation: If onions are from a new harvest, post-ripen or dry them for at least two weeks before transport to reduce moisture content.

Regular monitoring of temperature and humidity during transit ensures optimal conditions are maintained.

Preventing Sprouting

Sprouting is a common issue during onion storage and shipping, particularly when exposed to ethylene gas or improper conditions. To prevent sprouting:

Cool, Dark Storage: Store onions in a cool (32-40°F (0-4°C)), dry, and dark environment to minimize sprouting triggers.
Ethylene Management: Avoid storing or shipping onions with ethylene-producing fruits like apples or pears, as ethylene can accelerate sprouting and spoilage. Consider using ethylene-absorbing materials or controlled atmosphere systems in the shipping container to reduce exposure.
Low Humidity: Maintain low humidity levels to discourage sprouting, ensuring the outermost scale leaves remain dry.

Interesting Fact: Onions are one of the few vegetables that can continue to grow after being harvested, making them particularly prone to sprouting if not handled correctly. Their sensitivity to ethylene gas means that shipping them with fruits like apples or bananas can trigger unwanted growth, emphasizing the need for careful cargo planning.

Odor Management Strategies

Onions are known for their strong odor, which results from sulfur compounds and essential oils. Effective management relies on existing practices:

Ventilation and Temperature Control: Proper ventilation (60-80 air circulations/hour) and temperature control (32-40°F (0-4°C)) minimize the evaporation of essential oils, reducing odor intensity.
Container Hygiene: Thoroughly clean the shipping container before loading to prevent odor contamination from previous cargoes.
Sealing: Seal the container properly to contain odors and prevent them from affecting other cargo or the transport environment.
Dedicated Containers: Where possible, ship onions in containers dedicated to produce or with compatible cargo to avoid odor transfer.

These strategies help maintain a pleasant shipping experience and prevent odor-related issues.

Packaging and Handling

Proper packaging and careful handling are vital to protect onions from damage and maintain their quality:

Packaging: Use breathable materials like wide-meshed jute fabric or plastic bags, crates, or boxes. Avoid plastic wrapping or non-breathable materials, as they trap moisture and reduce shelf life.
Handling: Handle onions with care to avoid bruising, which increases respiration and self-heating. Rough handling can lead to internal decay and spoilage.
Stacking and Spacing: Keep stacks of bags or boxes at five feet or less to prevent pressure damage. Store bagged or boxed onions at least one foot away from walls and other pallets to ensure proper air movement.

These practices minimize physical damage and maintain airflow during transit.

Interesting Insights

Self-Heating Risk: Onions can self-heat due to respiration, releasing heat and CO2. Without proper ventilation, this can create a cycle of increased respiration and spoilage, making airflow critical beyond just moisture control.
Vidalia Onions: Vidalia onions, grown only in a specific region of Georgia due to unique soil and climate conditions, require extra care during shipping to preserve their sweet flavor, often involving refrigerated transport and careful handling.
Historical Significance: Onions have been used for thousands of years, not only as food but also for medicinal purposes and in mummification in ancient Egypt, highlighting their cultural importance.

Conclusion

Shipping onions requires careful consideration of ventilation, temperature, humidity, sprouting prevention, odor management, and disease control. By following these best practices and leveraging advanced technologies like controlled atmosphere systems and IoT monitoring, shippers can ensure onions arrive at their destination in top quality, ready for consumers to enjoy. Understanding onion physiology, such as their sensitivity to ethylene and risk of self-heating, further enhances the ability to maintain quality throughout the supply chain.