Freeze-drying

Freeze-drying involves sublimation, a process you learned in high school science and likely thought little about since. Product is first frozen at low temperature and then placed under vacuum. This is where the sublimation takes place. The process evaporates the ice. The ice crystals pass into the gaseous phase without first becoming liquid. Applying heat at the proper stage accelerates sublimation Low temperature condenser plates remove the vaporized ice crystals from the vacuum chamber by converting them back to a solid.

Individually quick freezing (IQF) is technology that has dissolved into the invisibility of the consumer's everyday expectations.

Before the advent of IQF, frozen fruits, vegetables and seafood often came frozen in lumps. Freshness, taste, and product integrity suffered for the cause of preservation Frigoscandia Equipment, today a Northfield, Minn., unit of FMC FoodTech, introduced the technology with the FloFreeze IQF freezer, and it has changed the image of frozen food quality ever since.

This revolutionary process eliminated blocks and frozen clusters of product. It enabled processors to clean, trim and freeze-in the nutrients of fruits and vegetables sometimes within hours of harvest. The process arrested the natural degradation process, making the frozen product at times superior to fresh.

The drying of products in the chemical and allied industries is not a final step presenting little difficulty. In many manufacturing processes drying is the final operation but it is not only a matter of removing moisture. Prevention of the physical appearance of the dry product frequently is of great importance and determines the drying method selected. In many cases the nature of the product is the controlling factor; for example, in drying food products the effect of the drying process on proteins, carbohydrates, fats, sugars, enzymes or vitamins may be the deciding factor, rather than economy of heat or first cost of equipment. The procedure varies with the product - its physical qualities, degree of wetness, and value.

Each group of materials has its own class of driers. Liquids containing dissolved solids and thin slurries carrying suspended matter are usually handled in drum or spray driers. Sludge and pastes may be mixed with dried materials until they crumble, and this mixture is then dried like solids. Wet solids are frequently dried in rotary driers, cylinders lying lengthwise, through which a current of heated air or flue gases travels. Compartment driers are closets or even rooms in which the material is spread on trays or in shallow pans; in the drying of dyes, for example, the same pan may be used for given colour exclusively. Separate pans are used for different colours, but the drier itself may be used for all. The operation is discontinuous; in order to make it continuous, the pans may be placed on trucks traveling on rails, and these are pushed through a tunnel in which warm air circulates. The belt drier and the chain drier are efforts in the same direction.