The Dehydration of Food


List benefits of dehydrated foods

Describe the role of air temperature and circulation in dehydration

Compare different methods of dehydration

Explain how pretreating foods improves dehydration

Demonstrate how to store dried foods

Compare different methods of rehydrating foods






Steam blanching



Syrup blanching

Benefits of Dehydration

Longer storage

Drying foods preserves food without for longer storage

Smaller size and weight

Drying decreases weight and bulk


Time savers

Can be prepared in a fraction

Dehydration in History

Sun drying is the oldest method of dehydration

the first mechanical food drying was in 1795

Large scale dehydration began to preserve food for armies in World War I

Typical home methods

The oven

The sun

Special dehydration appliance

Principles of dehydration

Temperature and air must be monitored to avoid bacteria growth & spoilage

If food is dried too slowly, bacteria have time to multiply and cause spoilage

Temperatures too high = caseharden

Cook the outside of food and food forms hard outer layer trapping moisture

Most foods are sliced into thin pieces to speed the drying process

Fruits that are dried whole such as grapes, are poked with holes to allow moisture to escape

Sulfiting, sulfuring, blanching


When food is soaked in a solution of water and sodium metabisulfite or sodium bisulfide = sulfiting

Maximum of 30 minutes to soak or food can become mushy

Disadvantage is extends drying times 15-20% due to water the food absorbs

Food placed on large trays that are stacked together and covered; burning sulfur that contain sulfur dioxide gas = sulfuring

Method used by most commercial fruit dryers

Takes 1-4 hours; food is dried outdoors either by sunlight or in a dryer to help decrease fumes

Food maintains original shape and color

Food placed in a perforated basket over boiling water and blanched by steam = steam blanching

Shortens the time needed for drying by relaxing the tissue walls for moisture to escape

Less water is added to food, drying time is shorter and vitamins and minerals are lost

Commonly used for vegetables

Cut fruit soaked in hot solution of sugar,
corn syrup, water and then dried = syrup

Methods of Dehydration

Sun drying is an effective way of dehydration

Room drying is another way to

dehydrate foods

Oven drying is also an option

Dehydrators are a relatively new invention that is now the safest and most effective

Dehydrofreezing is a method used by food processing industries.

It is a combination of partial drying and freezing

Food has the same moisture content, but does not mold

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