Transcript Freezing - University of Rhode Island

Freezing Fruits and
Vegetables at Home
Adapted from:
Cooperative Extension Service
College of Family and Consumer Sciences
University of Georgia
MARTHA SMITH PATNOAD, MS, CP-FS
CE FOOD SAFETY EDUCATION SPECIALIST
401-874-2960
[email protected]
NICOLE RICHARD, MS
RESEARCH ASSISTANT
401-874-2977
[email protected]
DEPT OF NUTRITION AND FOOD SCIENCES
UNIVERSITY OF RHODE ISLAND
8/2010
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Advantages of Freezing
 Many foods can be frozen.
 Good natural color, flavor and
nutritive value retained.
 Texture usually better.
 Takes less time
 Easy to do
 Foods can be frozen in any
quantity
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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

To prevent color and flavor changes, as
well as loss of some nutrients, enzymes
should be controlled

Enzymes are small proteins in foods that
start or help with reactions, such as those
that cause browning, off-flavors, ripening,
mushiness, etc

Are slowed down but not destroyed during
freezing.
.
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How Freezing Affects Food
Enzymes in Vegetables
 Are
destroyed by blanching which is
a quick heat and quick cooling
Enzymes in Fruits
 Usually
controlled the addition of
sugar and antioxidants such as
ascorbic acid ( vitamin C) or ascorbic
acid mixtures
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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.
 Food becomes mushy as large ice
crystal growth damages cells
 Moisture is pulled out of the food
 Other quality losses speeded up due to
higher temperatures.
 Moisture Loss
 Freezer burn – tough and dry, but safe.
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General 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. Keep work areas, containers, utensils
clean
3. Follow established directions.
4. Freeze foods immediately after prep.
5. Do not overload freezer

Freeze amount that will freeze in 24 hours
(2 to 3 pounds of food per cubic foot).
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Freezing Guidelines, cont.
Pack already frozen foods together to
prevent thawing
7. Place unfrozen foods in contact with
surfaces and in coldest parts of freezer
8. Leave space around packages so cold
air can circulate.
9. Arrange frozen foods so that the foods
frozen longer can be used first
10. Check thermometer
11. Time of storage- 1 year at 0 F
6.
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Packaging
 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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Packaging
 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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Packaging
 Bags
 Wraps
» plastic (such as polyethylene)
» heavy-duty aluminum foil
» laminated paper- “freezer paper”
 Good
for firm, non-juicy foods.
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Packaging
 Vacuum Sealers
- Always defrost in the refrigerator
- Cut several holes in the
plastic so
environment in
the bag is not
“air-free”
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Packing Foods
 Food must be cool
 Pack in serving size quantities.
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Packing Foods to be Frozen
 Pack foods tightly –
 Avoid trapped air (oxygen)
 Allow for headspace as food may
expand except:

uneven vegetables like
broccoli and asparagus
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Packing Foods- Sealing
 Press all air from bagged foods.

Except for headspace.
 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.

Always label with date and contents
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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

Ascorbic acid ( Vitamin C)

Heating the fruit

Ascorbic Acid Mixtures
-“Fruit Fresh” and others
- Have some other added ingredients.
-Follow package directions to obtain correct
strength
Do not work as well:
 Citric acid
 Lemon juice
 Sugar syrup
 Salt/vinegar solution
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Sweetened Packs for Fruit
 Sugar 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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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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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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