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Factors Affecting Dehydration1) Surface Area- smaller food piece, more rapid rate of moisture loss 2)Temperature- Hotter the air- more moisture it will hold before becoming saturated. 3)Air Velocity- Faster air velocity, more rapid rate of moisture removal 4) Humidity of Drying Air- Drier the air, the more moisture it can absorb before it becomes saturated. 5) Atmospheric Pressure and Vacuum- If temp is maintained constant, decrease in pressure will increase rate of boiling. Drying Methods: Sun drying: used mostly in dry, warm climates. Very slow drying method (several days). Used mostlyfor fruits/veg n fish. Risk of invasion by insects, birds, rodents,microorganismsSpray Drying: produce greatest quantities of commercially dehydrated foods. Only used for liquids; Skim milk, coffee,tea and eggs Tray (Air) Drying: Food placed on trays/racks is exposed to heated air. Can be fast/ requires heated air w/ a relative humidity. Lower than that of the product to be dried. Ie; pasta, vegetables, fruit, spices. Drum Drying: Food paste applied to heated drum in thin layer. Drum rotates, picks up food material. Dried food is scraped off drum. Dehydrated mashed potatoes/ some ready 2 eat cereals, dried potato flakes. Freeze Drying:Water is removed from food in frozen state w/o transition 2 liquid stage first. Called SUBLIMATION. Accelerated under vacuum conditions. During freeze drying, food remains rigid during dehydration, subliming water leaves voids where ice crystals were located. Vacuum Microwave Drying: Combination of vacuum and microwaves, producing high quality products with less nutrient loss, better flavour retention, and less colour change. Extrusion (Cooking) Drying: Food is passed thru tube, under pressure, that is heated by steam. Caused starch gelatinization and cooking of product. Forced thru narrow tube (Puffed).Hygroscopic: Because of their low water activity, dehydrated foods readily pick up moisture. Packaging thus most protect agPsychrophiles grow well in cold temperaturesPPsychrotrophs have adapted to living and multiplying in cold environments, mesophiles grow well in moderate Thermophiles grow best at high temperaturesainst oxygen/lightPreservation of Food with Ionizing Energy FFood Irradiation: RRadiant Energy:Refers to the emission and propagation of energy through matter or space by electromagnetic disturbances EElectromagnetic Spectrum of Radiation- organized scale where we find energy ranging from radio waves, microwaves, visible light to ionizing radiationMicrowaves: Travel in straight lines & pass through air, glass, paper and plastic, but reflected by metals. Absorbed by water (polar molecule), causing it to vibrate. Heat is generated by the intermolecular friction generated from the vibrating water (polar) molecules in food. Microwaves are absorbed by food up to a depth of 5 to 7.5 cm.