Black Mold in Onion Storage: Aspergillus niger Risks and Handling

Expert perspective: Alexander Samsonov, Agricultural Storage Engineer. View LinkedIn profile.

Black, powdery growth on the neck or outer scales of an onion is commonly associated with Aspergillus niger. The problem is especially relevant in warm production regions and when bulbs enter storage damp, damaged or exposed to condensation.

Black mold symptoms on stored onions

How Black Mold Develops

UC Integrated Pest Management describes black mold primarily as a post-harvest condition. Moisture on the bulb, wounds created during harvesting and handling, delayed drying and large temperature changes all increase the opportunity for infection. Condensation can place moisture between the dry outer scales, where the fungus develops.

What to Check Before Making a Storage Decision

Depth of damage: inspect whether symptoms are limited to dry outer scales or extend into fleshy tissue.
Bulb condition: soft, water-soaked or foul-smelling bulbs may also have secondary bacterial decay.
Lot uniformity: determine whether the problem is isolated or distributed through the batch.
Temperature and moisture history: review rain exposure, curing, loading temperature and condensation events.

Practical Risk-Reduction Measures

Separate visibly damaged and soft bulbs from sound product.
Reduce bruising and excessive drop heights during handling.
Do not delay curing and drying after harvest.
Maintain stable storage and transport temperatures to reduce condensation.
Keep airflow uniform through the stored product instead of over-drying only the easiest air paths.
Monitor the lot frequently and plan unloading order according to condition.

Food-safety and treatment decisions must follow local regulation and professional assessment. A storage system cannot restore onions that were loaded wet, severely damaged or already affected by advanced decay.

Storage Conditions Depend on the Operating Strategy

For long-term cold storage, UC Davis recommends approximately 0 °C and 65–70% relative humidity for dry onions, with adequate air circulation. India also uses controlled warm-storage concepts. ICAR-DOGR reports a design point of 27 ± 2 °C and 60–65% RH with controlled air circulation. The correct choice depends on onion variety, storage duration, market route, energy economics and post-storage behaviour.

Planning an Onion Storage Project?

Agrovent engineers ventilation, cooling and automatic climate control around the onion variety, harvest condition, storage period, building and local climate. Review our vegetable storage solutions or send your capacity and location to the Agrovent India office on WhatsApp.