Moisture regulation 181 mildew and fungus. For example, if a solid is very water soluble(such as a sugar coating), dissolution into the adsorbed layer can trigger irreversible water uptake and subsequent deliquescence, given the appropriate conditions. Selection of the proper desiccant can be inexpensive insurance for protecting packaged food products, thus resulting in improved quality 9.7.1 Sources of moisture in packaging Those involved in food packaging applications face a confusing array of variables when selecting moisture adsorbents (desiccants), as moisture regulation is a multi-faceted challenge. More specifically, sources of water permeation into a closed package or container can be attributed to moisture from (i) the product itself, (ii) any material(such as felt, foam, paper, etc. )used to support or retain the product, and (iii) permeation through the protective barrier of the package. With the goal of selecting the appropriate desiccant, moisture contributed by the product environment(ambient moisture)and the package (bound moisture)must be considered independently Ambient moisture emperature and relative humidity are two of the most influential environmental factors affecting product integrity and must be controlled to match the conditions of optimum product preservation and performance Before selecting the correct desiccant, it is imperative to know the conditions surrounding the shipment and storage of the product. Furthermore, at the time of packaging, it must be noted that the product is sealed in the conditions of the packaging room The moisture content of the air can be defined by its relative humidity, equal to the ratio(expressed as a percentage) of the partial pressure of water vapour present in the air to the saturated vapour pressure. The most useful combined measure of temperature and relative humidity is the dewpoint, that is, the temperature at which the actual vapour pressure equals the saturated vapour pressure. As the temperature drops, the saturation water vapour pressure decreases. Any additional drop in temperature will give rise to condensation, as the amount of water in the air has then exceeded the saturation point. Condensation provides the most dramatic visual observation of the effects of moisture damage. An effective desiccant will adsorb water vapour from the air in a package, lowering the relative humidity to the point where condensation will no longer occur or the threshold relative humidity is never exceeded under the conditions to which the package will be exposed As a general rule of thumb, designing the package and the desiccant to aintain an internal relative humidity of 10-12% at normal room temperature conditions(70oF)will provide adequate protection. It is strongly suggested that the desiccant supplier be contacted to discuss the elements of the package and the level of protection requiredmildew and fungus. For example, if a solid is very water soluble (such as a sugar coating), dissolution into the adsorbed layer can trigger irreversible water uptake and subsequent deliquescence, given the appropriate conditions. Selection of the proper desiccant can be inexpensive insurance for protecting packaged food products, thus resulting in improved quality. 9.7.1 Sources of moisture in packaging Those involved in food packaging applications face a confusing array of variables when selecting moisture adsorbents (desiccants), as moisture regulation is a multi-faceted challenge. More specifically, sources of water permeation into a closed package or container can be attributed to moisture from (i) the product itself, (ii) any material (such as felt, foam, paper, etc.) used to support or retain the product, and (iii) permeation through the protective barrier of the package. With the goal of selecting the appropriate desiccant, moisture contributed by the product environment (ambient moisture) and the package (bound moisture) must be considered independently. Ambient moisture Temperature and relative humidity are two of the most influential environmental factors affecting product integrity and must be controlled to match the conditions of optimum product preservation and performance. Before selecting the correct desiccant, it is imperative to know the conditions surrounding the shipment and storage of the product. Furthermore, at the time of packaging, it must be noted that the product is sealed in the conditions of the packaging room. The moisture content of the air can be defined by its relative humidity, equal to the ratio (expressed as a percentage) of the partial pressure of water vapour present in the air to the saturated vapour pressure. The most useful combined measure of temperature and relative humidity is the dewpoint, that is, the temperature at which the actual vapour pressure equals the saturated vapour pressure. As the temperature drops, the saturation water vapour pressure decreases. Any additional drop in temperature will give rise to condensation, as the amount of water in the air has then exceeded the saturation point. Condensation provides the most dramatic visual observation of the effects of moisture damage. An effective desiccant will adsorb water vapour from the air in a package, lowering the relative humidity to the point where condensation will no longer occur or the threshold relative humidity is never exceeded under the conditions to which the package will be exposed. As a general rule of thumb, designing the package and the desiccant to maintain an internal relative humidity of 10–12% at normal room temperature conditions (70ºF) will provide adequate protection. It is strongly suggested that the desiccant supplier be contacted to discuss the elements of the package and the level of protection required. Moisture regulation 181