Freezing is a method of long-term food preservation where the temperature of the food is reduced below its freezing point. This stops microbial growth and slows chemical changes that cause food to spoil. Key steps in the freezing process include sorting, washing, blanching vegetables to inactivate enzymes, packing into moisture-proof containers, and storing at -18°C or below. Fruits can be packed sweetened in syrup or sugar, or unsweetened. Vegetables are typically blanched before packing. Frozen foods maintain quality for 8-18 months if stored at proper temperatures.

1. Freezing of Fruits and Vegetables
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2.  WHAT IS FREEZING?
• It is a unit operation.
• Temparature of the food is reduced below its
freezing point generally to -18 °C or below.
• Change in state(Liquid state to Solid state).
• Allows preservation of taste, texture, and nutritional
value in foods.
• Provide a signifant extended shelf life.
• Retards growth of microorganisms.
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3. GRAPH SHOWING FREEZING PROCESS
FOR FOODS
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4. • Freezing point is defined as the temperature at
which the first ice crystal appears and the liquid at
that temperature is in equilibrium with the solid.
• Freezing time is defined as time required to lower
product temperature from its initial temperature to a
given temperature at its thermal center.
• Freezing rate is defined as the ratio of difference
between initial and final temperature of product to
freezing time.
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5. Principles of Freezing
 Does not sterilize food.
 Extreme cold (0 oF or -18 oC) colder):
◦ Stops growth of microorganisms and
◦ Slows chemical changes, such as enzymatic
reactions.
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6. Advantages of Freezing Foods
 Many foods can be frozen.
 Good natural color, flavor and nutritive value
can be retained.
 Texture usually better than for other methods
of food preservation.
◦ But this is personal preference.
 Foods can be frozen in less time than they can
be dried or canned.
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7. Disadvantages of Freezing Foods
 Texture of some foods is undesirable because
of changes due to the freezing process.
 Initial investment and cost of maintaining a
freezer is high.
 Storage space is limited by how much the
freezer will hold.
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8. Chemical changes
• Enzymes in vegetables
 Are destroyed by heat, called blanching, before packaging and freezing.
• Enzymes in fruit
 Usually controlled by ascorbic acid (vit- C) or some other additives.
 Fruits are usually not blanched.
• Rancidity
 Another natural change that causes off-flavors, particularly in fatty foods.
 Best control is to keep as much air out of the package as possible.
Texture Changes
• Expansion of food
Water freezes and expands foods.
Vegetables with very high water content do not freeze well. Ex. Celery,
lettuce and tomatoes
Vegetables with lower water content become more compact. Ex. Spinach
and broccoli
• Ice crystals
How Freezing Affects Food
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9. Freezing Fruits
 Frozen in many forms
◦ Whole, sliced, crushed, juiced.
 Best quality
◦ Optimum maturity and freshness.
◦ Immature or over ripe both produce lower quality
when frozen.
 Wash and work with small amounts at a time to
preserve best quality.
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10. Raw material
Water
Removal of low quality
produce
Sorting - grading
PackagingSugar addition
Washing
Sale
Frozen storage -18˚C
Freezing
Flow diagram of freezing process for fruit-based product. 10

11. Sweetened Packs For Fruit
 Syrup Pack
◦ Better texture.
◦ Not needed for safety.
◦ Fruits should be covered with syrup.
Place crumpled water-resistant paper in top of container.
 Sugar Pack
◦ Sliced soft fruits (strawberries, peaches, etc.) make
their own syrup when mixed with the right
proportion of sugar.
◦ Layer fruit and sugar in bowl or pan.
◦ Allow mixture to stand 15 minutes to make juice
or “syrup” before packaging.
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12. Unsweetened Packs For Fruit
 Dry Pack
◦ Good for small whole fruit such as
berries that don’t need sugar.
◦ Simply pack into containers and
freeze.
 Dry Tray Pack
◦ Fruit pieces may be frozen individually,
in single layer, on a tray first.
◦ Freeze until firm then package in rigid
container or bag.
◦ Will pour out of container easily when
frozen.
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13. Freezing Vegetables
 Select young, tender, high-quality vegetables.
 Sort for size and ripeness.
 Wash and drain before removing skins or shells.
 Wash small lots at a time, lifting out of water.
DO NOT SOAK.
 Work in small quantities, preparing as directed.
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14. Raw material
Water
Removal of low quality
produce
Sorting - grading
Packaging
Hot water & Steam
Washing
Sale
Frozen storage -18˚C
Freezing
Peeling-Trimming-Cutting-Sizing
Blanching(85-90˚C)
Deep in cold water (1-5 ˚C)
Flow diagram of freezing process of vegetable-based product.14

15. Types of Pack for Vegetables
 Dry Pack
◦ Pack after the vegetables are blanched, cooled,
and drained.
◦ Pack quickly, pushing air out of package as you
work towards top.
 Tray Pack
◦ After draining, spread pieces in a single layer
on a shallow pan.
◦ Freeze firm.
◦ After first hour, check often.
◦ Package quickly, pushing air out as you work.
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16. Fruits
• Most frozen fruits maintain high quality for 8 to 12
months
• Unsweetened fruits lose quality faster than fruits packed
in sugar or sugar syrups
Vegetables
• Most vegetables will maintain high quality for 12 to 18
months at 0°F or lower
• Use your home-frozen vegetables before the next year’s
crop is ready for freezing
Recommended Storage Times
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17. Thawing Foods For Serving
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18. Fruits
 Best if served with ice crystals present.
 Thaw:
o In refrigerator 6 to 8 hours per pound of fruit in syrup.
o At room temperature 1 to 2 hours per pound.
o At room temperature in cool water 1/2 to 1 hour per
pound.
o In microwave oven - follow manufacturer’s
instructions.
 Dry sugar packs thaw faster than syrup packs.
 Unsweetened packs thaw the slowest.
 When used in recipes, allow for added sugar and more
juice.
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19. Vegetables
 Most vegetables can be cooked without
thawing.
 Leafy greens cook more evenly if partially
thawed.
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20. Packaging Materials
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 Moisture-vapor resistant
 Durable and leak-proof
 Not become brittle and crack at low temperatures.
 Resistant to oil, grease, or water
 Protects foods from absorption of off-flavors or odors
 Easy to seal and mark

21. Types of Packaging Materials
 Rigid Containers
o Plastic freezer containers.
o Wide-mouth canning/freezing jars.
Good for liquids or soft, juicy, or liquid-
packed foods.
May be reusable.
Hold their shape and can be stored upright.
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22. Types of Packaging Materials
 Non-Rigid Containers
o Bags
o Wrappings – plastic (such as polyethylene),
heavy-duty aluminum foil, laminated paper
 Good for firm, non-juicy foods.
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23. Labels
 Name of product
 Added ingredients
 Form of food - halves, whole,
ground, etc.
 Packaging date
 Number of servings or
amount
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24. Consider
• Size
• Shape
• Efficiency
• Defrosting features
• Available floor area
• Amount of freezer space needed
Other features to consider
• Self defrosting or manual defrost.
• Receptacle clips prevent accidental disconnecting.
• Door locks.
• Drains for defrosting.
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Selection Of Freezer

25. Types of Freezers
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26. Refrigerator - Freezer
Combination
Air Blast Freezer Belt Freezer
Plate Freezer Liquid Nitrogen Freezer Immersion Freezer 26

27. Location and Placement of Freezer
 Place in convenient, cool, dry, well-ventilated
area.
 Do not place by stove, range, water heater or
in the sun.
 Do not push flush against wall. Leave space
for air circulation and cleaning.
 Be sure freezer is level.
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28. Freezer Emergencies
 If know power will be off, set freezer controls on -10oF
to -20oF immediately.
 Do NOT open the door.
 Foods stay frozen longer if freezer is full, well insulated
and in cool area.
◦ Full freezer - keeps 2 to 4 days.
◦ Half-full freezer - 24 hours.
 Place dry ice on boards or heavy cardboard on top of
food.
 Do not touch dry ice to skin.
 Do not open freezer.
 Room should be ventilated.
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29. Best Advice for Freezing
 Freeze foods quickly.
◦ Set freezer temperature at -10o F at least 24
hours ahead of freezing large quantities of
fresh food.
◦ Spread packages out around the freezer, until
frozen, then stack.
 Hold at 0oF for best quality.
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