Technologies and methods for storing onions in a vegetable store

How to Preserve Onion Quality and Freshness: Proper Post-Harvest Preparation and Storage Technology

Do you want your onions to stay fresh, firm and market-ready - and stand out on supermarket shelves or wholesale markets?
Then professional post-harvest handling and proper storage are essential. The shelf life, flavor, color and overall quality of onions depend not only on the right microclimate equipment but also on correct preparation before the crop enters the storage facility.

Below is a complete guide to preparing onions for long-term storage, especially relevant for growers in India, Africa and the Middle East, where high temperatures and humidity make onion storage particularly challenging.

How to Prepare Onions for Storage

1. Cleaning and Sorting After Harvest

Immediately after harvesting, onions must be cleaned of soil, weeds and debris. This step prevents fungal growth and the spread of microorganisms that cause spoilage.
If you detect partially damaged bulbs, you can sometimes save them by removing the infected outer scales.

2. Drying (Curing)

Only fully mature and well-dried onions should be placed in a vegetable store. Proper curing helps prevent mold, rot and neck breakdown.
Curing requires active ventilation and is adjusted depending on onion variety and local climate.

Process:

Freshly harvested onions are ventilated with outside air.
The temperature of the pile rises to about +20°C due to warm external airflow entering the storage chamber.

If unripe green onions are mixed into the batch, they cannot be stored under standard conditions. For these, drying temperature should be increased to +30°C to avoid neck rot, which develops quickly at +22…+25°C.

Typical curing duration:

6 weeks
8–9 hours of ventilation per day
Air exchange capacity: 200–250 m³/t per hour

Once curing is completed, maintenance ventilation of 4 hours per day is generally sufficient.

3. Gradual Cooling Phase

After drying, begin lowering the temperature step by step — 0.5°C per day until it reaches +20°C in the storage chamber.

To prevent moisture condensation, ventilate with outside air for 10–15 minutes every 3 hours during the cooling stage.

Storage Options for Onions

Once onions are cleaned, sorted and fully cured, they are ready for storage.
Microclimate systems must maintain both temperature stability and optimal humidity, because onions are extremely sensitive to excess moisture and sudden climate fluctuations.

High humidity leads to mold and rot, which spread quickly from one bulb to another. To avoid this, ventilation should operate 15 minutes every two hours.

Microclimate Technologies We Typically Use in Onion Storage Projects

Agrovent implements several advanced systems designed specifically for long-term onion storage:

Combined Ventilation System
Aspiration Wall Technology
Dragon-M High-Pressure System

Each project is engineered individually, taking into account:

onion variety
volume of harvest
climate zone
storage building design
operational goals
energy efficiency requirements

We fine-tune all parameters at the design stage to ensure maximum shelf life and minimal losses.

Key Storage Parameters You Should Always Follow

Regardless of the storage system, some rules are universal:

No temperature differences inside the pile
Cooling must start only after drying is fully completed
Optimal relative humidity: 75%
Storage temperature: 0 to +1.5°C

Following these guidelines helps maintain firmness, prevent sprouting, and significantly extend shelf life — especially important for regions with hot climates.