Fluidized-bed Freezing
Fluidized bed freezing is a modification of air-blast freezing. Solid food particles ranging
in size from peas to strawberries can be fluidized by forming a bed of particles 1-5 in.
Deep on a mesh belt (or mesh tray) and then forcing air upward through the bed at a rate
sufficient to partially lift or suspend the particles in a manner somewhat reminiscent of a
boiling liquid. If the air used for fluidization is appropriately cooled, freezing can be
accomplished at a rapid rate. An air velocity of at least 375 lineal ft/min is necessary to
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fluidize suitable particles, and an air temperature of about –34°C is common. Bed depth
depends on the ease with which fluidization can be accomplished, and this in turn depends
on size, shape, and the uniformity of particles. A depth of slightly more than 1 in. is
suitable for easily fluidized particles, such as peas and whole kernel corn; a depth of 3-5
in. is used for partially fluidizable particles, such as green beans; and a depth of 8-10 in.
can be used for nonfluidizable products, such as fish fillets. Although freezing time varies
with conditions, some representative times for various products are listed