Postdrying Treatments

Treatments of finished fruits vary with the kind of fruit and intended use of the products. The addition of an anti-caking agent, usually calcium stearate at less than 0.1% concentration, is necessary to prevent caking of most dehydrated fruits.

Sweating of dehydrated fruits is a treatment to equalize moisture of the batch. It is usually accomplished by keeping the dried fruit in bins or boxes. Bins are also used for secondary drying to reduce moisture levels of particulate fruits from 10-15% to 3-5%, a range at which drying rates are limited by slow diffusion of water. Temperatures of about 40°C and airflow provided by a blower fan, of about 33 m/min, suit the nearly dry product. These conditions minimize the risk of heat damage at a stage when fruit products are most susceptible to degradation.

Screening is often required to remove the unwanted size portion of the dried product. Removal of unwanted size pieces, or fines, is usually accomplished by passing the dry product over a vibrating wire cloth or perforated metal screens and collecting the fractions separately. Fines may be used in other products, or sometimes represent a loss.

The acceptable fraction passes onto the final inspection operation to remove foreign materials, discolored pieces, or other imperfections such as skin, carpel, or stem particles. Manual and visual selection of most dehydrated products is necessary and is carried out by inspectors while the product is moving along on a continuous belt. In addition to inspectors, magnetic devices are usually installed over the belt to remove ferrous metal contaminants.

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