DRYING Flashcards
(26 cards)
Dehydration
Moisture removal by:
Evaporation
Osmosis
Sublimation
Dehydration
Reduction of moisture content (Inhibition of):
Microbial Activity
Enzyme Activity
a general term applied to all methods of removing moisture from the food which inhibits the growth of microorganisms.
Drying
achievement of a low moisture level in food (below 13%) to prevent spoilage by molds.
Dehydration
- Most widely used drying method in agricultural processing operation
- Food is laid and turned in drying beds or mats
Solar Drying (Sun Drying)
Commercial Drying (4) CVOF
Conventional drying
Vacuum drying
Osmotic drying
Freeze-drying
uses heat to evaporate the water in food
Conventional drying
dehydrates foods to very low moisture levels of 1-3% through the use of a vacuum.
Vacuum Drying
Examples of vacuum-dried foods
Milk, tomato paste, orange juice, coffee
The method preserves flavor and color and increases shelf life.
Vacuum Drying
2 disadvantages of vacuum drying
1) Expensive
2) Requires dehydrated food to be stored in airtight containers to prevent rehydration by drawing moisture from air
it reuses a strong syrup with a high sugar concentration that osmotically draws water from the food being dried.
Osmotic drying
caused by osmotic pressure from concentrated solutions of sugar and salt
Osmotic dehydration
The removal of water from food when it is in a frozen state usually under a vacuum
Freeze-drying
Food is frozen then placed in a vacuum where the ice sublimates.
Freeze Drying
To minimize color changes during dehydration
1) Blanching
2) Sulfuring
exposure of cut fruits to the smoke fumes created by burning sulfur flowers to retain a bright color during drying
Sulfuring
Reqs for dehydration (3)
1) Low relative humidity
2) Warm air temperature
3) Air is circulating above the food
Aside from preserving qualities:
- Decrease in height and weight
- Change in texture and flavor/color/odor
Factors affecting the drying process (TRTV)
Temperature
Relative humidity of air
Time of Drying
Velocity of Air
The best temperature of drying is 110-115 deg F but exact temperatures will vary with the type, size, and thickness of food and the method of drying
Temperature
varies with the type of food and the method and stage of drying.
Relative humidity of the air
It is usually high at the start of drying and becomes less as drying progresses
Relative humidity of the air
this is a directly proportional to the desired dryness of the product and the initial moisture content of the product
Time of drying
this is proportional to the transfer of heat from the food to the environment.
Velocity of Air
