Freeze, Drum, and Tray Drying

Alternative dehydration processes for the encapsulation of flavors include drum (contact) drying, tray drying, and freeze drying [98]. While these processes do not find major use in the industry, they are used in certain applications. These processes and their potential use for flavor encapsulation will be briefly discussed. 

Contact dryers are dryers in which the wet material is dried by direct contact with a heated surface. Heat transfer to the wet material is mainly by conduction from this surface through the bed or layer of wet solids. This is in direct contrast to convection tray dryers since no hot gas is required as a source of heat in contact dryers, gas flow through the system can be low and ultimately limited to the vapor evaporated from the wet material [100]. 

Specifically in drum drying, material is dried on the surface of an internally heated revolving drum. The material, in fluid, slurry, or paste-like form, is spread in a thin layer on the surface of the drum so that at no time is the drying rate governed 

Steam pressure or heating medium temperature, which governs the temperature of the drum surface 

Speed of rotation, which determines the time of contact between the film and the preheated surface 

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