1. Freezing Fruits and Vegetables at Home

2. Advantages of Freezing
Many foods can be frozen
Easy to do
Not time-consuming
Foods can be frozen in any quantity
Retention of
color
flavor
nutritive value
texture
While many foods can be frozen, some foods do not freeze well (cream will separate, the yoke in shell eggs will thicken and will not mix well afterward, lettuce become mushy; raw meats maintain quality longer than cooked counterparts because moisture is lost during cooking).
Discuss how the color of red meat can change during frozen storage from red to brown due to oxidation, freezer burn, or extended storage time.
Discuss how frozen vegetables and cooked foods can experience dulling of color if improperly packaged or lengthy storage due to product drying.
Freezing does not destroy nutrients. Store foods at 0°F or lower to retain vitamin content, color, flavor and texture.

3. However… Does not destroy spoilage organisms
Does not destroy Clostridium botulinum
Only inactivates organisms
Rapidly freeze
Maintain ≤ 0°F
Important to keep work space clean
Thaw in refrigerator
Freezing does not destroy spoilage organisms (such as bacteria, yeasts, and molds) present in food; it only inactivates them.
The best way to freeze foods is quickly to maintain its quality. Food stored constantly at 0°F will always be safe. Only the quality suffers with lengthy freezer storage. Rapid freezing minimizes ice crystal formation = better quality.
However, once thawed, these organisms become active and will multiply under the right conditions to levels that can lead to foodborne illness.
It is important to work in a clean space to prevent contaminating the food.
The best way to thaw frozen food is in the refrigerator. You can also safety thaw frozen food in cold running water (make sure to check the water frequently to make sure that it stays cold and change the water every 30 minutes to keep it cold) or in the microwave as long as the food is immediately cooked (because some parts of the food may become warm and begin to cook during microwaving).
It is important to handle thawed items as you would any perishable food and to thaw properly (at refrigerated temperature) to keep microbial activity to a minimum. 3 3

4. Getting Started For best quality Optimum maturity and freshness
Immature or overripe = lower quality
Wash and drain first
DO NOT SOAK
Do not use galvanized, copper or iron equipment w/ fruits
Select products of best quality at optimum maturity and freshness. Freezing does not improve quality.
Select varieties suitable for freezing.
Freeze them before they lose their freshness.
If cannot be frozen immediately, refrigerate them.
Wash and drain all fruits and vegetables first.
Wash small lots at a time through several changes of cold water. Lift the produce out of the water so the dirt washed off will not get back on the food. Do not let them soak.
Work in small quantities; enough for only a few containers at a time, to prevent loss of quality and nutrients.
When preparing fruit for freezing do not use galvanized, copper or iron equipment. The acid in the fruit could react with the metals forming harmful compounds or off-flavors. 4 4

5. Enzymes Naturally present in foods
Small proteins that promote chemical reactions
Activity can lead to deterioration of food quality
Freezing slows enzyme activity
Stop enzymatic activity before freezing
Chemical and physical changes occur in fruit and vegetable tissue as they mature. Initially they may help the produce reach its peak quality, but then they can also contribute to its decay. Freezing will only slow enzyme activity, and for many foods, this is sufficient. In other foods, especially vegetables, enzymes should be destroyed (by heat) prior to freezing in order to prevent undesirable color, flavor and texture changes.
Examples of enzymatic changes in fruits and vegetables:
Formation of “lignin” or tough, stringy texture in some vegetables (asparagus, spinach, broccoli).
Browning of cut apples, bananas, peaches, cherries, pears.
Softening of fruits from breakdown of natural pectins, caused by pectin-degrading enzymes.
Development of potent, unpleasant odor compounds in cut garlic, leeks and onions, and overcooked broccoli, cabbage and Brussels sprouts.
Breakdown of colors to less desirable forms in bright green vegetables.
Brown to dark gray discoloration of cut white potatoes.

6. Control Enzymes Enzymes in Vegetables Enzymes in Fruits Blanching
quick heat & quick cool
Enzymes in Fruits
Ascorbic acid
Commercial mixtures
Citric acid
Lemon juice
Vegetables are commonly blanched to stop enzyme activity before freezing.
Fruits are commonly treated with chemicals, such as ascorbic acid, to inactivate enzymes responsible for fruit browning.

7. Prevents Flavor and Color Changes
Blanching
Prevents Flavor and Color Changes
Inactivates enzymes
Removes microorganisms
Required blanching times
Under-blanching
stimulate enzymes
worse than no blanching!
Over-blanching
Cooks the product
Blanching (scalding vegetables in boiling water or steam for a short time) stops enzyme actions which can cause loss of flavor, color and texture.
Blanching cleanses the surface of dirt and organisms, brightens the color and helps retard loss of vitamins. It also wilts or softens vegetables and makes them easier to pack.
Blanching time is crucial and varies with the vegetable and size.
Underblanching stimulates the activity of enzymes and is worse than no blanching.
Overblanching causes loss of flavor, color, vitamins and minerals. 7 7

8. How to Blanch Vegetables
Boiling Water
1 gallon water : 1 lb vegetables
Timing:
If boiling = begin timing immediately
Wait for water to come back to a boil
Have the water in the blancher vigorously boiling before adding the prepared vegetable. Use a lid after adding vegetables, to keep the water boiling vigorously.
Small quantities are recommended to avoid the vegetables being in hot water any longer than necessary, since the goal is not to cook them. One pound of vegetables will require at least 1 gallon of boiling water. If the water loses its boil when the vegetable is added, wait for the water to boil before starting to count the blanching time. If it takes too long to come to a boil (more than a minute), use less vegetable to the amount of water. If you do not wait for the water to come back to a boil, you could under-blanch your vegetables and actually stimulate enzymes to work faster, rather than destroy them.
If you are blanching several loads in a row, remember to add water back to the blancher as it boils away. 8 8

9. How to Blanch Vegetables
Steam Blanching
1 - 2 inches boiling water in bottom of pan
Vegetable in a single layer in basket
Start timing when covered
Heating in steam is recommended for a few vegetables, such as mushrooms. For broccoli, pumpkin, sweet potatoes and winter squash, both steaming and boiling are satisfactory methods. Steam blanching takes about 1½ times longer than water blanching.
To steam, use a pot with a tight lid and a basket that holds the food suspended over (not touching or in) the boiling water. Put an inch or two of water in the pot and bring the water to a boil.
Put the vegetables in the basket in a single layer so that steam reaches all parts quickly. Cover the pot and keep heat high. Start counting steaming time as soon as the lid is on.
Takes 1-1/2 times longer than water blanching. 9 9

10. How to Blanch Vegetables
Microwave Blanching
Not recommended
Uneven heating
Won’t inactivate all enzymes
Improper blanching will affect quality
USDA currently does not have microwave blanching recommendations published.
Most microwave ovens have unevenness in cooking pattern and the goal of blanching is to be sure to destroy enzymes, not just heat and stimulate them to faster action. 10 10

11. COOL QUICKLY AND THOROUGHLY
After Blanching
COOL QUICKLY AND THOROUGHLY
Plunge basket into cold water
cold running water
iced water
Cooling time = blanching time
Drain thoroughly
As soon as blanching by any method is complete, vegetables should be cooled quickly and thoroughly to stop the cooking process. To cool, plunge the basket of vegetables immediately into a large quantity of icy, cold water, at least 60oF or below. (Three to 4 gallons of icy water is best.)
Use cold running water or iced water. If ice is used, about one pound of ice for each pound of vegetable is needed. Cooling vegetables should take the same amount of time as blanching.
Drain vegetables thoroughly after cooling. Extra moisture can cause a loss of quality when vegetables are frozen. 11 11

12. Preventing Fruit Darkening Sweetened Options
Syrup Pack
Percent sugar to water depends upon sweetness desired
Sugar Pack
Sprinkle sugar over fruit
Allow mixture to stand to make “syrup” before packaging
Most fruits have a better texture if packed in sugar or syrup. However, this is not necessary to safely preserve the fruit.
Think about the intended purpose for the fruit you are freezing. Fruits packed in a sugar syrup will have a more liquid consistency, whereas those packed in dry sugar or unsweetened are best for most cooking purposes because there is less liquid in the product.
Sugar syrups help fruit maintain its flavor, color and texture. A 40 percent syrup is recommended for most fruits. Lighter syrups are desirable for mild-flavored fruits to prevent masking of flavors. Heavier syrup may be needed for very sour fruits. (You may also use ascorbic acid in your syrup). To make the syrup, dissolve sugar in lukewarm water, mixing until the solution is clear. Chill syrup before using. Use just enough cold syrup to cover the prepared fruit after it has been placed in the container (about ½ cup of syrup per pint). To keep fruit under the syrup, place a small piece of crumpled parchment paper or other water resistant wrapping material on top, and press fruit down into the syrup before sealing the container. SEE PAGE 93 IN BALL BLUE BOOK FOR % SUGAR SYRUP TABLE.
Sugar packs: sprinkle sugar over the fruit and mix until the juice is drawn out and the sugar dissolved. Soft sliced fruits, such as strawberries, peaches, and cherries will yield sufficient syrup for covering if the fruit is layered with sugar and allowed to stand for 15 min. Some small whole fruits may be coated with sugar and frozen. 12 12

13. Preventing Fruit Darkening Unsweetened Options
Commercial mixtures
Ascorbic acid
(1/2 tsp = 1500 mg )
Citric acid (3x)
Lemon juice (6x)
Heating the fruit
Packs:
Pectin syrup
Water
Unsweetened juice
Some fruits such as peaches, apples, pears and apricots darken quickly when exposed to air and during freezing. They may also lose flavor when thawed. There are several ways to prevent darkening of fruit and flavor loss.
Unsweetened packs generally yield a product that does not have the plump texture and good color of those packed with sugar. The fruits freeze harder and take longer to thaw. However, some fruits (raspberries, blueberries, cranberries, rhubarb, and figs give a good quality product w/o sugar).
Commercial mixtures are special anti-darkening preparations, usually made of ascorbic acid mixed with sugar or with sugar and citric acid.
Ascorbic acid or vitamin C: FOR SPECIFIC USAGE AMTS OF ASCORBIC ACID, VISIT UGA WEBSITE OR SEE FREEZING CHAPTER IN “SO EASY TO PRESERVE.”
Is preferred for being effective in preventing discoloration in most fruits
It will not change the flavor of the food, as larger amounts of citric acid or lemon juice will do.
Available at some drugstores or where freezing supplies are sold. Tablets may be more readily available, but can be more difficult to dissolve. They do need to be finely crushed before use. Fillers in the tablets may make the syrup cloudy, but this is only a quality issue.
It dissolves easily in cold water, juices, or sugar syrups
For example, to use with apples, dissolve 1500 mg (or ½ tsp) ascorbic acid in 3 T water and sprinkled over fruit.
Citric acid (not as effective as ascorbic acid) need 3x’s more citric acid than ascorbic acid to prevent discoloration
Lemon juice (not as effective as ascorbic acid):
Contains both ascorbic and citric acids
An equal amount of crystalline ascorbic acid is 6x’s more effective than lemon juice
Can interfere with natural fruit flavors.
Salt and vinegar solutions are no longer recommended. The solution may help prevent browning initially, but light colored fruits can eventually become gray in appearance.
Heating the fruit: Steaming over boiling water is enough to retard darkening in some fruits (for example, apples). This works best for fruits that will be cooked before use. Steam the fruit just until hot.
Packing in pectin syrup, water, juice or :
Pectin syrup is often used for fruits, such as strawberries or peaches, that retain their texture better than if frozen in water or juice. 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:
Texture will be mushier.
Color poorer.
Freezes harder, takes longer to thaw. 13 13

14. Unsweetened Packs for Fruit
Dry or Tray Pack
Spread on trays to freeze until firm
Pack into containers and freeze
Will pour out of container easily
Retain shapes
The dry pack is good for small whole fruits such as berries, that give a good quality product without sugar. Simply pack the fruit into a container, seal and freeze.
Even fruit pieces dry-packed in this manner may “clump” together if not frozen very rapidly. Moisture left clinging to the fruit pieces will facilitate this “clumping” as the fruit pieces freeze together with external ice crystals.
A tray pack is an alternative that may make the fruit easier to remove from the container. 14 14

15. Sugar Substitutes Added to pectin syrup, juice or water packs
Added just before serving
These do not help with color retention or texture, like sugar does
Use amounts on product labels or to taste
Sugar substitutes (aka “artificial sweeteners”) may be used in any of the unsweetened packs. Both saccharin and aspartame work well in frozen products or they can be added to the fruit just before serving.
Artificial sweeteners give a sweet flavor but do not furnish the beneficial effects of sugar, such as color protection and thickness of syrup.
Labels on the products give the equivalents to a standard amount of sugar. Use directions on the container to determine the amount of sweetener needed. 15 15

16. How Freezing Affects Food
Rancidity -meat, fish, poultry
Textural Changes
Water freezes and expands
Ice crystals cause cell walls to rupture
Produce with high water content does not freeze well: celery, lettuce, tomatoes, melons
Another goal in freezing for maintaining optimum texture is to minimize the size of ice crystals formed – that is, to promote the formation of the smallest ice crystals possible. Large ice crystals do more damage to food cells and cause softer, mushier textures.
Foods that don’t freeze well (and the effects of freezing on their texture) are summarized at:

17. How Freezing Affects Food
Fluctuating Freezer Temperatures
Ice in food thaws and re-freezes
Ice crystals get bigger
= rupture cell walls of food
= mushy/softer texture
Quality losses due to higher temperatures
Improperly Packaged
Moisture loss
Freezer burn
Quality, not safety issue
Here is a review of how freezing can adversely the quality of foods.
One of the biggest contributors to poor texture in frozen fruits and vegetables is large ice crystals.
(The package of frozen strawberries pictured on this slide represents the appearance of large ice crystals formed outside the pieces of food. This is typical of food stored in a freezer with fluctuating temperatures, where moisture is pulled from the product and refreezes outside the cells.)
The air in a freezer is very dry. If foods are improperly packaged so they are exposed to the air in the freezer, or moisture is pulled through the packaging material from inside to outside the package, the food dries out. Freezer burn is an example of drying out of food tissue. Freezer burn often looks like a grainy, brownish or whitish spot on the surface of foods, where the tissues become dry and tough. Packaging in heavy-weight, moisture- and vapor-resistant wrap will prevent freezer burn. This dried surface area is very likely to develop off-flavors, but it will not cause illness. (Freezer burn is a quality issue, not a safety issue.)

18. Guidelines for Best Results
≤ 0oF
Freeze as soon as possible
In advance of freezing large quantities,
Set freezer ≤ -10oF
Do not overload freezer -2 to 3 lbs/ft3
Unfrozen foods in coldest parts
Leave space
FIFO
Check thermometer
Time of storage
Keeping food frozen at 0 degrees F or lower will minimize ice crystal growth that results when food temp. fluctuates too much while in the freezer
Freeze foods as soon as possible for best quality
If freezing a lot of items, lower the freezer temp in advance to prevent the items from increasing the temperature in the freezer. This will also allow the food to freeze more rapidly. Also, do not over load the freezer with unfrozen food. Add only the amount that will freeze within 24 hours, which is typically 2-3 lbs/ft3. Over loading slows down the freezing rate and foods that freeze too slowly may lose quality.
Place unfrozen foods in the coldest part of the freezer so they freeze quicker
Leave space around the food for the cold air to circulate, then when the food is frozen store the packages close together.
Date and label the food and practice First-In First-Out
Keep a thermometer in your freezer so you know it is at the correct temperature

19. Types of Packs Dry Pack Tray Pack after blanching, cool and drain
Package quickly, pushing air out
Tray Pack
after washing/draining, spread in a single layer on a shallow pan
Freeze firm
Package quickly
After you have blanched, cooled and drained the vegetable, spread in a single layer on shallow trays or pans
Place in the freezer just long enough to freeze firm. After the first hour, check often. Long exposure will result in loss of moisture.
Package quickly, leaving no headspace, then seal. Tray packed vegetables remain loose and can be poured from the container and the package re-closed.

20. Packaging Materials Moisture-vapor resistant Durable and leak proof
Not become brittle at low temperatures
Resistant to oil, grease or water
Protect foods from absorption of off-flavors or odors
Easy to seal
Foods for your freezer must have proper packaging materials to protect their flavor, color, moisture content and nutritive value from the dry climate of the freezer. The selection of containers depends on the type of food to be frozen, personal preference and types that are available. Do not freeze fruits and vegetables in containers with a capacity over one-half gallon. Foods in larger containers freeze too slowly to result in a satisfactory product.
To prevent evaporation and retain the highest quality in frozen foods, packaging materials should be moisture and vapor proof. Many packaging materials designed for frozen food, including most plastic bags, are not moisture and vapor proof, but are sufficiently moisture and vapor resistant to be used satisfactorily.
Containers suitable for freezing include:
Rigid containers made of aluminum, glass, or plastic. Exercise caution if using glass as it can break easily at freezer temperatures. Use wide-mouth dual purpose jars made for freezing (these jars have been tempered to withstand extremes in temperatures). Ice cube trays can be used to freeze small amounts of food. Freeze food until firm, then transfer to freezer bags.
Flexible bags or wrapping made of moisture/vapor resistant materials and heavy duty foil. These items are designed for freezer use, as indicated on the packaging. Heavy duty aluminum foil can be used, however, it can be torn or punctured easily so use an overwrap. Light weight household aluminum foil is not satisfactory for home freezing. 20

21. Packing Foods Food must be cool Pack in serving size quantities
Pack food tightly
Label and Date!
Cool all foods and syrup before packaging. This speeds up freezing and helps retain the natural color, flavor and texture of food.
Pack foods in quantities that will be used for a single meal. 21 21

22. Packing Foods to be Frozen
Cool first
Pack foods tightly
Press out as much air as possible
Some foods need headspace
Tight seal/closure
Using freezer tape
LABEL and DATE!
By cooling foods before freezing, the freezing process will be faster and the color and texture of the food will be retained better.
Pack foods tightly as you work towards the top of the container, leaving as little air as possible throughout the food in the package.
Some foods require headspace between the packed food and closure to allow for expansion of the food as it freezes.
Make sure the sealing edges are free from moisture or food so they make a good tight seal
If using tape, it must be freezer tape, which is designed for use in the freezer and remains effective at low temperatures
Label and date the food items! 22 22

23. How to Properly Thaw Food
Refrigerated temperature
= safest
= best quality
Microwave
In cold water
The safest way to thaw food is at refrigerated temperatures. Food must be kept at safe temperatures during defrosting. Food is safe while frozen, however, as soon as it begins to defrost and become warmer than 40F, any bacteria that was present before freezing can begin to multiply.
Food thawing at room temperature gives microorganisms the opportunity for growth and activity.
When food is thawed the ice crystals melt and the liquid is either absorbed back into the food or leaks out from the food. Slow thawing usually results in better return of moisture to the food.
Foods thawed in the microwave or by being placed in cold running water should be cooked thoroughly immediately after thawing. If thawing in cold water you need to continually check that the water is cold and the food will be thawed in 2 hours.
Another suggestion: thaw in a bag in cold water in the refrigerator. If not bagged, the tissues can absorb water resulting in a watery product.

24. Thawing Vacuum Sealed Packages
Only defrost in the refrigerator
Cut several holes in the plastic so environment in the bag is not “air-free”
Vacuum sealing involves the removal of air from the package prior to frozen storage. There can be a risk of C. botulinum if the package is not thawed properly. It is very important to thaw a vacuum sealed package at refrigerated temperatures only and to poke holes or cut an opening in the package so oxygen can get in. 24 24

25. Can food be refrozen once thawed?
Yes, it is safe to refreeze if:
Thawed in the refrigerator
After cooking
Purchased previously frozen meat, poultry, or fish at a retail store
No, it is not safe to refreeze if:
Thawed in the microwave
Thawed in cold running water
If food is thawed in the refrigerator it is safe to refreeze it without cooking, although there will usually be a loss of quality due to moisture loss during defrosting
If you purchase previously frozen food at a retail store, you can refreeze if it has been handled and transported properly and maintained in a cold environment. Do not keep perishable foods between 40 and 140 F for more than 2 hours. While it is safe to refreeze meat or poultry directly in it’s original retail packaging, keep in mind that this packaging is permeable to air and quality may diminish over time. For prolonged storage, overwrap these packages.
No, it is not safe to refreeze if food has been thawed in the microwave or in cold running water. This food should be cooked before refreezing.

26. What if the Freezer Stops?
The basis for safety is temperature
The food is still safe to use if:
Ice crystals remain
It is cold ( < 40°F)
Group frozen foods together
Cover the freezer with blankets to insulate
The basis for safety is the temperature at which thawed foods have been held and the length of time they were held after thawing.
You can safely refreeze foods that still contain ice crystals or if they are still cold (i.e. < 40F) and have been held no longer than 1-2 days at this temperature. To take the temperature, place a food thermometer between 2 bags of food. Another great option is to keep a freezer thermometer in your freezer so you know what the temperature is.
A full freezer should keep for 2 days and a half full freezer should keep for 1 day.
If the freezer is not full, group packages together so they retain the cold more effectively. Separate meats from other frozen foods so if they thaw their juices won’t drip onto other foods. You may want to put dry ice or bags of ice in the freezer. 25-lbs of dry ice in a 10 cubic foot freezer should hold the temp. below freezing for 2-3 days. Use caution when handling dry ice – don’t handle with bare hands as it will burn, be sure room is ventilated.
If you cover the freezer with blankets, be sure not to cover the air vent so when electricity comes back on the vent is not blocked.
To determine the safety of the food when the power is back on check their condition and temperature. If the food is partly frozen and has ice crystals it is safe to refreeze. If the food is cold (< 40F) it is safe to refreeze or use. Discard foods that have been warmer than 40F for 2 hours or foods that have come into contact with any raw meat juices.

27. Disclaimer and Credits
Trade and brand names are used only for information. The University of Rhode Island does 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:
Adapted with permission of the University of Georgia. Andress, E.L Freezing fruits and vegetables at home (slides). Athens, GA: The University of Georgia, Cooperative Extension Service.
Note from the author: (see slide 1 for author information)
If this slide set is used without changes, the citation should say “reprinted…”
If it is used with changes, please state “adapted” in the citation.