Desiccants such as silica gels, natural clays and calcium oxide are used with dry foods while internal humidity controllers are used for high moisture foods (for example, meat, poultry, fruits, and vegetables). Desiccants usually take the form of internal porous sachets or perforated water-vapor barrier plastic cartridges containing desiccants. They can also be incorporated in packaging material. Humidity controllers help maintain optimum in-package relative humidity (about 85% for cut fruits and vegetables), reduce moisture loss, and retard excess moisture in headspace and interstices where microorganisms can grow
The reaction needs of a proper content of humidity and it can be accelerated
by the presence of electrolytes. Catalysts are commonly used and the most
popular is the chlorine ion, which is usually added in the form of salt
These salts have the ability to absorb large amounts of water vapour when the relative humidity exceeds a certain value
If the relative humidity subsequently decreases, the absorbed water is released again. This mechanism allows the RH to be adjusted to a desired value, namely regulated.