DEHYDRATION TECHNIQUES

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DEHYDRATION TECHNIQUES
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DEHYDRATION TECHNIQUES

• Dehydration is one of the oldest methods of food
  preservation, and many cultures still dry food in
  the sun.

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• Drying is usually accomplished by the evaporation
  of water, but any method that decreases the
  amount of water activity in food is a form of
  drying. For example, heavy salting of fish will
  cause moisture to be drawn from the flesh. Most
  foods, how ever use heat to remove moisture. The
  goal is to deny micro-organisms the moisture they
  need to grow, and to deactivate enzymes.

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THE EFFECTS OF DEHYDRATING ON FOODS

• The main principle of drying is the evaporation
  of water, using higher than normal temperatures.
  As the water evaporates there is an increase in
  the concentration of solutes in the product. This
  increase can physically damage the food. This
  damage can be seen in the changed physical
  appearance of dried apples.

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DRYING CAUSES

• Denaturation of proteins
• a general loss of structure
• browning reactions
• discolouration

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METHODS OF DEHYDRATION

• Hot air bed - Solid foods are placed on
  perforated trays. Hot air is blown through the
  tray under carefully controlled conditions
  regulating the time and temperature.
• Spray-drying - Spray drying is used for liquid
  foods, such as milk. The finely sprayed food is
  blown into a hot air chamber, where it dries as
  granules and drops to the bottom for collection.
• Accelerated freeze-drying - Liquid food, eg.
  Coffee, is frozen very rapidly. Tiny ice crystals
  form in the food. These are quickly removed by
  turning them to vapour, as the food is heated in
  a vacuum.

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DEHYDRATED FOOD PRODUCTS

• There is a variety of dehydrated food products,
  such as
• mixed vegetables, peas, potato
• noodles/pasta
• soups
• fruits
• tea/coffee

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SOUPS AND PASTA
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VEGETABLES
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REHYDRATED POTATO
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SULTANAS
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SOUPS
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TOMATO SOUP
BEFORE AND AFTER
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PEAS
BEFORE AND AFTER
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MIXED VEGETABLES WITH PASTA
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STORAGE

• Dehydrated foods must be stored in in a cool, dry
  place. If foods have contact with moisture,
  micro-organisms will start to grow and reproduce
  again.

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ADVANTAGES

• Dehydrated foods are lightweight and usually have
  compact packaging.
• Cheap
• Convenient
• little effort needed to prepare
• long lasting
• easy to do at home

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• Dehydration of food is an effective method of
  preserving. Dehydrated foods can be used any time
  of year as they have a storage life of one to two
  years, depending of the type of food. Dehydrated
  foods can be used a lot in cooking as they are
  convenient and easy to prepare. If you have a
  dehydrator at home you can do your own foods,
  this is also cheap.