Onion is one of the vegetables that are relatively difficult to store during winter. In addition to traditional storage methods, utilizing natural cold conditions and maintaining proper temperature control can help ensure a successful winter storage, allowing for consistent supply to the market throughout the season.
Green onions have a high resistance to low temperatures, capable of withstanding as low as -20°C. When frozen at this temperature, they can gradually thaw at 0°C or above without losing cellular viability. This makes them well-suited for low-temperature storage. The ideal temperature for this method is around 0°C, with a relative humidity of 85% to 90%.
For micro-freezing storage, the suitable temperature range is between -3°C and -5°C. If low-temperature conditions are not available, green onions can be stored at room temperature for a short period, ideally in an environment with 80% humidity. However, higher humidity levels can lead to spoilage more quickly.
When storing green onions for extended periods, it's important to choose varieties with high soluble solids content and harvest them at the right time. Harvesting too early can reduce storage stability. Commonly used storage techniques include:
1. **Racking Method**: Suitable for small spaces and long-term storage. In open areas, sheds, or indoors, wooden poles or steel frames are used to create 2–3 tiers of shelves, each about 80 cm high. Dried onions are bundled into 7–10 kg groups and placed on the shelves, leaving space for ventilation to prevent decay. A tarp or grass cover is used to protect against rain and snow. Regular checks are necessary to remove any spoiled onions.
2. **Flatland Storage**: Dry sand, 3–4 cm thick, is spread on a shaded flat surface. Dried green onions are tightly packed in rows, with roots facing downward and spaced 1.5 meters apart. After arranging, 15 cm of sand is added around the roots. Once the inner part of the bundles cools slightly, straw curtains or covers are placed on top to protect from rain and sunlight.
3. **Shallow Ditch Storage**: A shallow ditch, 20–30 cm deep and 50–70 cm wide, is dug in a cool and ventilated area. Bundled green onions, weighing about 10 kg, are placed into the ditch and surrounded by corn stalks to help maintain a cool environment below 0°C. The top is covered with straw or corn stalks to provide insulation.
4. **Kiln Method**: After drying for several days, green onions are bundled into 10 kg units and placed in a dry, sunny, sheltered location to continue drying. Once the temperature drops, they are moved into a kiln. The kiln should be kept at around 0°C, with attention given to controlling heat and moisture.
5. **Cold Storage Method**: Pest-free, undamaged green onions are tied into 10 kg bundles and placed in boxes or baskets. These are then stored in refrigerated warehouses at 0–1°C with 80–85% humidity. Regular inspections are needed to promptly remove any spoiled onions.
No matter which storage method is used, maintaining a stable and low temperature is crucial. Avoiding repeated freezing and thawing is essential, as this can significantly increase losses and lower the quality of the stored onions.
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