Transcript Freezing - National Center for Home Food Preservation

Freezing Fruits and
Vegetables at Home
Cooperative Extension Service
The University of Georgia
College of Family and Consumer Sciences
Advantages of Freezing
 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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Advantages of Freezing
 Simple procedures.
 Adds convenience to food
preparation.
 Proportions can be adapted to needs
unlike other methods.
 Kitchen remains somewhat cool and
comfortable.
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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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How Freezing Affects Food
Enzymes in Vegetables and Fruits
 To
prevent color and flavor changes,
as well as loss of some nutrients,
enzymes should be controlled.
 Are slowed down but not destroyed
during freezing.
(Enzymes are small proteins in foods that start or
help with reactions, such as those that cause
browning, off-flavors, mushiness, etc.)
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How Freezing Affects Food
 Enzymes in Vegetables

Are destroyed by heat, called blanching,
before packaging and freezing.
 Enzymes in Fruits
Usually controlled by ascorbic acid (also
called vitamin C) or some other additives.
 Fruits are usually not blanched, but can be.

 People
like them raw and uncooked.
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How Freezing Affects Food
Rancidity
 Another natural change that causes off-
flavors, particularly in fatty foods.
 Not a common problem in fruits & veggies.
 Will continue to happen at freezer
temperatures, but slower than at warmer
temps.
 Best control is to keep as much air out of the
package as possible.
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How Freezing Affects Food
 Textural Changes
 The water in food freezes and
expands.
 Ice crystals cause the cell walls of
fruits and vegetables to rupture,
making them softer when thawed.
 Some vegetables with very high
water content do not freeze well:
celery, lettuce, some tomatoes.
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How Freezing Affects Food
Rate of Freezing is Very Important
Freeze Foods Quickly!
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Best Advice for Freezing
 Freeze foods quickly.
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.
 Set
 Hold at 0oF for best quality.
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Best Advice for Freezing
What happens when the freezer is
above 0oF ?
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Best Advice for Freezing
What happens when the freezer is
above 0oF ?
 Shelf life (storage time) for best
quality is shorter.
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Vegetable Storage
For same final quality:
Temperature
0o F.
5o F.
10o F.
15o F.
20o F.
25o F.
30o F.
Length of Storage
1 year
6 months
3 months
6 weeks
3 weeks
10 days
5 days
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How Freezing Affects Food
 Fluctuating Freezer Temperatures
 Ice in food thaws a little and then
re-freezes.
 Ice crystals get bigger each time.
 Mushiness because large ice crystal
growth damages cells more and more.
 Moisture pulled from product.
 Other quality losses speeded up due to
higher temperatures.
 Moisture Loss
 Freezer burn – tough and dry, but safe.
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Freezer Selection
 Consider
 Size
 Shape
 Efficiency
 Defrosting
features
 Available floor area
 Amount of freezer space needed
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Freezer Selection
 What size?
 General Rule - Allow 6 cubic feet of
freezer space per person in family.
 (3
cubic feet per person may be
adequate if other methods of food
preservation are used).
 Standard
Freezer Capacity:
35 pounds of frozen food per
cubic foot of usable space.
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Types of Freezers
 Upright
6
to 22 cubic feet
 Convenient
 Uses small floor space
 Easy to load and unload
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Types of Freezers
 Chest
6
to 32 cubic feet
 Takes more floor space
 More economical to buy
and to operate than upright
 Loses less cold air
when opened
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Types of Freezers
 Refrigerator - Freezer
Combination
2 to 6 cubic feet of freezer
space.
 Freezer may be above, below
or beside refrigerated area.
 Be sure temperature in freezer
can be maintained at
0 degrees F. or less.

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Types of Freezers
 Other features to consider
 Self
defrosting or manual defrost.
 Receptacle clips –
prevent accidental disconnecting.
 Door locks.
 Drains for defrosting.
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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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General Freezing Instructions
 Selection of Food
 Freezing does not improve quality.
 Choose highest quality available.
 Freeze promptly.
 Remember some foods don’t freeze well.
 Preparation
 Work under sanitary conditions.
 Follow recommended procedures.
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Packaging Materials
Good Qualities
 Moisture-vapor resistant.
 Prevents transfer of moisture and air in and out of
the package.
 Durable and leak-proof.
 Does 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 label.
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Types of Packaging Materials
 Rigid Containers
 Plastic
freezer containers.
 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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Types of Packaging Materials
 Non-Rigid Containers
 Bags
– plastic (such as polyethylene),
heavy-duty aluminum foil, laminated
paper
 Wrappings
 Good
for firm, non-juicy foods.
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Packing Foods to be Frozen
 Food must be cool before freezing.
 Ice
water bath after blanching.
 Pack in serving size quantities.
 Usually
up to 1 quart.
 Especially when whole package must
be thawed to get out what is needed.
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Packing Foods to be Frozen
 Pack foods tightly –
 Avoid trapped air (oxygen).
 Not to waste space.
 However, most foods need headspace
or room for some expansion at the
top, except




uneven vegetables like
broccoli and asparagus,
bony pieces of meat,
tray-packed foods,
and breads.
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Packing Foods to be Frozen
 Press all air from bagged foods.


Except for headspace.
Seal non-zippered bags by twisting the
loose top, and then folding the top of it
down over itself (gooseneck). Secure
with twist-tie, rubber band or string.
 Use tight lid on rigid containers.


Keep sealing edges clean and dry. Use freezer
tape over seams of looser-fitting covers.
Trapped food or liquids in sealing area will
freeze, expand, and loosen seal.
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Labels
 Name of product
 Added ingredients
 Form of food - halves,
9/15/02
Ground Beef
1 pound
whole, ground, etc.
 Packaging date
 Number of servings or
amount
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Freezing Guidelines
1. Freeze foods at 0oF or lower.

24 hours in advance of freezing large
quantities of food, set freezer at -10oF or
lower.
2. Freeze foods immediately after prep.
3. Do not overload freezer with unfrozen
food.

Freeze amount that will freeze in 24 hours
(2 to 3 pounds of food per cubic foot).
4. Pack already frozen foods together so
they do not thaw.
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Freezing Guidelines, cont.
5. Place unfrozen foods in contact with
surfaces and in coldest parts of freezer.
6. Leave space around packages so cold
air can circulate.
7. When packages are frozen, organize
freezer into types of food.
8. Arrange frozen foods so that the foods
frozen longer can be used first.
9. Keep a frozen foods inventory up to
date.
10. Check thermometer periodically.
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Freezing Fruits
 Frozen in many forms –
Whole, sliced, crushed, juiced.
 Best quality –
 Optimum maturity and freshness.
 Immature or overripe both produce lower
quality when frozen.
 Wash and work with small amounts at a time
to preserve best quality.

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Preventing Fruit Darkening
During Preparation
(Peeling, slicing, etc.)
1 tsp (3000 mg) ascorbic acid to one
gallon of cool water
 Commercial ascorbic acid mixture
 Heating the fruit


The following do not work as well:
 Citric acid solution
 Lemon juice
 Sugar syrup
 Salt/vinegar solution
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Preventing Discoloration
During Freezing
 Ascorbic Acid
 Most economical
 Powdered or tablet form
 1/2 t. powdered ascorbic acid = 1500 mg
 For tablets, use number needed for
desired milligrams
 (for

example, 3 x 500 mg tablets = 1500 mg)
Tablets must be crushed well
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Preventing Discoloration
During Freezing
 Ascorbic Acid
 Use

amount specified for each fruit.
In syrup or liquid packs - add powdered
ascorbic acid to the covering liquid.
 Usually ½ tsp (1500 mg) per quart of syrup.
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Preventing Discoloration
During Freezing
 Ascorbic Acid (con’t)

In sugar or dry packs, dissolve the powdered
ascorbic acid in 3 T. in cold water and
sprinkle over fruit.
 In
sugar packs, before adding sugar.
 Usually ¼ to ½ tsp (750 to1500 mg) per 3 T. water
for each quart of fruit.

For crushed fruit, purees or juices, mix the
powdered ascorbic acid with the prepared
fruit.
 Usually
about ¼ tsp (750 mg) or less per qt. of fruit.
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Preventing Discoloration
During Freezing
 Ascorbic Acid Mixtures
 “Fruit Fresh” and others.
 These have some other added ingredients.
 Follow package directions to obtain correct
strength of ascorbic acid.
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Preventing Discoloration
During Freezing
 Citric Acid or Lemon Juice
 Not as effective as ascorbic acid.
 May mask flavors of fruits.
 Steaming
 Best for fruits that will be cooked before use.
 Follow directions in freezing publications for
times.
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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.
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Preparing Peaches in Syrup
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Sweetened Packs for Fruit
 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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Unsweetened Packs for Fruit
 Dry Pack
 Good
for small whole fruits
such as berries that don’t need
sugar.
 Simply pack into containers and
freeze.
 Or may be frozen individually, in
single layer, on a tray first.
 “Tray
pack” – next slide
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Dry Tray Pack for Fruit
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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Dry “Tray” Pack for Fruit
Can remove only the amount needed at one
time.
 Fruit pieces retain shapes.
 Fruit pieces do not “clump” as when packed
directly into containers or with sugar syrup.

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Unsweetened Packs for Fruit
 Pectin Syrup
Good for strawberries and peaches.
 Mix 1 package powdered pectin and 1 cup
water. Bring to boil, boil 1 minute. Remove
from heat, cool and add 1-3/4 cups more
water.

 Water or Unsweetened Juice Packs
Texture will be mushier.
 Color poorer.
 Freezes harder, takes longer to thaw.

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Packs for Purees or Juices
 Pack as is, with or without sugar.
 Add ascorbic acid if light-colored.
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Sugar Substitutes
 May be used in the pectin syrup, juice
or water packs.
 Or could be added just before serving.
 These do not help with color retention
or texture, like sugar does.
 Use amounts on product labels or to
taste.
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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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Preventing Flavor and Color
Changes in Vegetables
Blanching
 Primary method to destroy enzymes for
vegetables.
 Will also soften hard veggies to make
packaging easier.
 Will also remove some microorganisms.
 Under-blanching can be harmful; it will
stimulate enzymes and not destroy them.
Check required blanching times for each food.
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How to Blanch Vegetables
Use specific directions.
Work in small quantities.
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How to Blanch Vegetables
 In Boiling Water
Use blancher with lid or a
kettle with basket and lid.
 Have 1 gallon water per 1 lb. of vegetables.
 Place vegetables in blanching basket.
 Lower vegetable into vigorously boiling
water. Put lid on. Water should hardly stop
boiling or return to a boil within a minute.
 If water keeps boiling, begin timing
immediately. Otherwise, wait for water to
come back to a boil.

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How to Blanch Vegetables
 Steam Blanching
Use kettle with tight lid and basket.
 1” to 2” of boiling water in bottom
of pan.
 Vegetable should be in a single
layer in basket.
 Start timing when covered.


Takes 1-1/2 times longer than water
blanching. Check times, however, for
each food.
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How to Blanch Vegetables
 Microwave Blanching
 Not widely recommended at this time.
 May not be effective – enzymes not
inactivated completely by uneven heating.
 Usually does not save time.
 Have

to do very small quantities.
If you have directions from a source you
trust, try small quantities at first and see if
you like the quality after a period of frozen
storage.
 This
is not a safety issue, as long as frozen
food is always stored frozen, but improper
blanching will affect quality.
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How to Blanch Vegetables
 After
blanching in water or steam, cool
immediately in cold water.
 Change water frequently or use
running water or iced water (1 lb. ice
per 1 lb. vegetable).
 Cooling time should be the same as
the blanching time.
 Drain thoroughly.
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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.
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Types of Pack for Vegetables
 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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Thawing Foods for Serving
 Fruits
 Best if served with ice crystals.
 Thaw:
 In
refrigerator - 6 to 8 hours per pound of fruit in
syrup.
 At room temperature - 1 to 2 hours per pound.
 At room temperature in cool water - ½ to 1 hour per
pound.
 In microwave oven - follow manufacturer’s
instructions.
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Thawing Foods for Serving
 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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Thawing Foods for Serving
 Vegetables
 Cook
without thawing.
 Corn-on-the-cob should be partially
thawed so cob will be hot.
 Leafy greens cook more evenly if
partially thawed.
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Oh No!
You’ve done all this work …
and
the freezer stops running!
60
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.

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Freezer Emergencies
 If power interruption will be longer
than 1 to 2 days:
 Use
dry ice:
 50
lbs. - keeps full 20 cubic foot freezer
below freezing for 3 to 4 days.
 50 lbs. - keeps half-full freezer for 2 to 3
days.
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Freezer Emergencies
 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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Refreezing Thawed Foods
 Texture will not be as good.
 General Rule:
 Refreeze
if freezer temperature is still
40oF or below OR if ice crystals are
still present in the food.
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Disclaimer and Credits
 Disclaimer:

Trade and brand names are used only for information. The Cooperative
Extension Service, University of Georgia College of Agricultural &
Environmental Sciences and College of Family & Consumer Sciences,
and the U.S. Department of Agriculture do not guarantee nor warrant
published standards on any product mentioned; neither does the use of
a trade or brand name imply approval of any product to the exclusion of
others which may also be suitable.
 Document Use:



Permission is granted to reproduce these materials in whole or in part
for educational purposes only (not for profit beyond the cost of
reproduction) provided the author and the University of Georgia receive
acknowledgment and this notice is included:
Reprinted (or Adapted) with permission of the University of Georgia.
Andress, E.L. 2003. Freezing fruits and vegetables at home (slides).
Athens, GA: The University of Georgia, Cooperative Extension Service.
This material is based upon work supported by the Cooperative State
Research, Education, and Extension Service, U.S. Department of Agriculture,
under Agreement No. 00-51110-9762.
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