When outside air infiltrates a cold store, the inside moisture content decreases as its temperature falls below dew point and water condenses on to the cold surfaces, particularly the cooling coils in the refrigeration system.

As the air circulates around the chill store it warms, reducing its relative humidity. The warmer air draws moisture from any surface it can, including the produce itself.  This leads to product weight loss - as much as 20% - and cells become less turgid, affecting the appearance, quality and shelf-life of the produce, all of which reduce the value of the stock. 

The solution lies in raising the relative humidity to a level that's in equilibrium with the stored produce. Optimal conditions vary according to the specific type of fruit, vegetables, flowers or other food product being stored but, typically, a humidity of around 95%RH at a temperature just above freezing is required. Produce stored in warmer conditions benefits from a humidity level around 75%RH.

Commercial markets and the many modern distribution depots run by supermarket chains benefit from effective humidification, as do chilled display cabinets and open counters, helping to ensure that produce quality is maintained right through the supply chain.