Food Preservation

1
Food Preservation
2
How Food Spoils

• Spoiled foods result from chemical changes and
  from the growth of tiny forms of life called
  microorganisms.

3
Why Foods are preserved

• All methods of food preservation are designed to
  produce healthful, flavourful products.

4
How foods are preserved

• The chief methods of food preservation include
• (1) Cold Storage
• (2) Canning
• (3) Freezing
• (4) Drying
• (5) Freeze-drying
• (6) Curing.

5
Cold Storage

• Keeps food fresh at low temperatures. These
  temperatures, usually ranging from -1 to 10 C,
  do not stop spoilage. But they slow
  microorganisms' growth and enzyme action.

6
Cold Storage

• The cold storage life of foods depends on the
  type of food, the storage temperature, and the
  amount of moisture present in the air of the
  storage room.
• All sorts of foods can be preserved using this
  method, such as apricots, pears, butter, cheese,
  and eggs.

7
Canning

• Has two aims (1) to sterilize food, or make it
  germ-free, and (2) to keep air away from it.
  Heating food to high temperatures destroys
  microorganisms and stops enzyme action.

8
Canning

• To keep air away from food, canners pack it in
  air tight metal or glass containers. They remove
  the air from the containers and seal them in
  airtight lids.

9
Canning

• Sealing keeps out microorganisms and helps
  prevent oxidation of the food. Most canned foods
  keep well for more than a year.

10
Freezing

• It ranks after canning as one of the most widely
  used methods of food preservation. Home makers
  and commercial food processors freeze most kinds
  of fruit and vegetables, and some kinds of meat,
  fish, poultry, and dairy products.

11
Freezing

• Food companies also freeze a variety of precooked
  foods ranging from French-fries to complete meat
  dinners.

12
Drying

• Or dehydration, removes most of the moisture from
  food. It also reduces the size and weight of
  foods, making them easier to transport and store.

13
Drying

• Sun- Drying is the oldest method of drying food.
  The food is first spread on trays and exposed to
  the sun. After several days, enough moisture will
  have evaporated from the food to make safe for
  storage. Many fruits, some vegetables, and some
  fish can be sun-dried.

14
Drying

• Kiln-Drying uses heat from a furnace or stove to
  evaporate moisture from food. The furnace or
  stove stands on the lower floor of a building
  called a kiln. The food is put on the slatted
  floor of the upper stories, and heat rises
  through the openings between the slats.

15
Kiln-Drying

• This method may take several days. During this
  period the food is moved and turned several times
  to make sure it becomes thoroughly dry.

16
Drying

• Dehydrators take less time than the other means
  of drying to process the same amount of food.
  Some dehydrators use a partial vacuum to make
  water evaporate at a low temperature so fewer
  chemical changes caused by heat take place.

17
Freeze-Drying

• It removes water from the food while it's still
  frozen. The frozen food is cooled to about -29
  C. Then it is placed on trays in a vacuum
  chamber, and heat is carefully applied.

18
Freeze-Drying

• In this method, the frozen water in the food is
  evaporated without melting. It takes from 4 to 12
  hours, depending on the type of food, particle
  size, and the drying system used. This method
  usually produces higher quality dried foods, but
  it costs more than other drying methods.

19
Curing

• Slows the growth of microorganisms inside food,
  and often destroys many of those on the food
  surfaces. Curing consists of salting, smoking,
  cooking, and drying. Or some combination of these
  treatments. Sometimes certain chemical compounds
  other than salt may be used, but their amount is
  regulated.

20
Curing

• Salt must be used in large amounts to control
  microorganism growth. Because salt has a strong
  taste, food processors can use large amounts
  where it adds flavour such as beef. They usually
  put the food in salt-water solutions to soak up
  the salt. Or rub dry salt into the food.

21
Curing

• Sugar in large amounts slows the growth of
  microorganisms. Cooks and processors add sugar or
  syrup to jams and jellies, or usually to canned
  or frozen fruits, to help preserve them. Sugar
  also improves the flavour of these foods.
  Condensed milk contains sugar as a preserving
  agent.

22
Curing

• Vinegar is used to pickle green tomatoes,
  cucumbers, cauliflower, onions, sardines, and
  other foods that taste good sour. Acetic acid in
  vinegar slows microorganisms growth.

23
Curing

• Wood Smoke contains chemicals that slow the
  growth of microorganisms. But smoking changes the
  odor and flavour of food. It's only used to
  preserve meats or fish, because it doesn't ruin
  the flavours of these products. Meat to be smoked
  is hung in a smokehouse. A slow burning fire
  produces the smoke.

24

• This report is an extract from
• The World Book Encyclopedia
• A subsidiary of Field Enterprises, Inc.

25

• This Project was done by
• Rand Dalqamouni
• School Ein Jalout El- Shamleh
• Class Eleventh IT Grade c.
• Under the supervision of
• Ms. Tahani Zaiter