Cooling Dehydrating

Products such as dehydrated potato flakes require cooking rather than frying. The cooking follows the blanching and cooling operations and use times and temperatures that best accomplish cell aggregation with minimal cell rupture. Typically, cooking involves the application of live steam (100°C) for times ranging from 20 to 30 min, dependent on slab thickness and potato solids content, to obtain a cooked product for mashing.

Potatoes are mashed immediately after cooking to minimize cell rupture. Additives such as emulsifiers that prevent gluiness/stickiness by complexing free starch (8), chelating agents that prevent after-cooking darkening by complexing metal ions (9), and antioxidants that prevent oxidation of potato components (10) are incorporated during the mashing process. Cooked potatoes are mashed in equipment that blends the potato tissue with additives until an appropriate consistency is obtained for application to the dehydrating drums for drying.

Dehydration to flakes consists of drying a thin layer of the mashed potato material to less than 6% moisture on a steam-heated rotating drying drum. This process results in a sheet of dried potato tissue 0.015 to 0.025 cm thick (11), which is then reduced to flakes via size-reduction/ grinding equipment.

When processing potato chips or French fries, the frying operation is usually followed by a short cooling period before proceeding to the next operation. This cooling generally occurs on conveyor belts at ambient conditions in the plant (Fig. 4). French fries may undergo removal of excess surface oil in 70°C flowing air immediately following frying and before the cooling operation. Cooled French fries then enter a freezing operation. This operation rapidly reduces the product temperatures to —15 to — 7°C with refrigerated air or by application of liquid nitrogen (- 50°C) directly to the product surface.

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