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                          TECHNICAL PAPER #59
                       UNDERSTANDING HOME-SCALE
                        PRESERVATIONS OF FRUITS
                            AND VEGETABLES
                                PART I
                         CANNING AND FREEZING
                              Eric Rustin
                          Technical Reviewers
                            Joel M. Jackson
                             George Rubin
                          William G. Schultz
                             Published By
                    1600 Wilson Boulevard, Suit 500
                     Arlington, Virginia 22209 USA
                 Tel: 703/276-1800 . Fax: 703/243-1865
               Understanding Home-Scale Preservation of
                         Fruits and Vegetables
                     Part I: Canning and Freezing
                          ISBN: 0-86619-278-6
              [C]1988, Volunteers in technical Assistance
This paper is one of a series published by Volunteers in Technical
Assistance (VITA) to provide an introduction to specific
state-of-the-art technologies of interest to people in developing
countries. The papers are intended to be used as guidelines to
help people choose technologies that are suitable to their situations.
They are not intended to provide construction or implementation
details. People are urged to contact VITA or a similar
organization for further information and technical assistance if
they find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and illustrated
almost entirely by VITA Volunteers technical experts on a purely
voluntary basis. Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time. VITA staff included Margaret Crouch as
project manager, Suzanne Brooks handling typesetting, layout, and
graphics, and James Butty as technical writer/editor.
The author of this paper, VITA Volunteer Eric P. Rusten, a former
Peace Corps Volunteer to Kenya and Nepal, is a graduate student
at Washington University in St. Louis, Missouri. The reviewers
are also VITA Volunteers. William G. Schultz is a mechanical
engineer and has specialities in food processing applications;
George Rubin is a product developer with Dell Products Incorporated
in New Jersey, having retired as manager of the Welch
Foods Inc. in Westfield, New York; Joel Jackson is a food scientist
with Food Preservation Systems in Windsor, Maryland.
VITA is a private, nonprofit organization that supports people
working on technical problems in developing countries. VITA offers
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to their
situations. VITA maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster of
volunteer technical consultants; manages long-term field projects;
and publishes a variety of technical manuals and papers.
Preserving the surplus food that is often available at harvest
time helps ensure a continuous supply of food throughout the
year. There are several methods of food preservation, including
canning, freezing, pickling, drying, and curing (smoking or salting).
All these preservation methods aim to prevent or at least
slow down spoilage. Careful attention to the proper techniques of
preserving and storing also helps ensure that the food stays as
nutritious and palatable as possible.
This paper, the first of a two-part series, discusses principles
of canning and freezing fruits and vegetables at home, for home
use. The companion paper presents the principles of drying and
curing. Guidelines are given to help readers select the best
possible method of preserving the produce they have available.
Drying, smoking, salting, and pickling have been used for thousands
of years to keep food from spoiling. Canning or jarring to
preserve food is much more recent. It was first developed in 1809
by Nicholas Appert, a French chef who learned that food cooked
in sealed containers would keep for extended periods of time. Although
Appert, like his predecessors, did not know why food
spoiled or why their technique worked, this early method was
quite successful and has changed little since it was developed.
Today, it is one of the most popular methods of preserving food.
In the early twentieth century, freezing became a popular method
for short-term preservation of food, but its high cost has kept
it from becoming as common as canning in many parts of the world.
The rotting of fruits and vegetables has four major causes. Three
of these--molds, yeasts, and bacteria--are microorganisms found
in great numbers in the air, soil, and water. They are the primary
causes of food spoilage. Enzymes, the other major cause of
food spoilage, are complex chemical substances found in all living
cells, including the skins and flesh of fresh fruits and
vegetables. All preservation methods are aimed at preventing
these four agents from acting upon the food being preserved.
Molds are fungi that grow in warm, moist food. As the mold grows,
it slowly consumes the food matter and brings about changes in
the character of the food. This promotes the growth of other
microorganisms, eventually leading to complete food spoilage.
The ideal temperature for mold growth is between 10 and 38[degrees]C (50-100[degrees]F).
But at temperatures of 90[degrees]C or more, all molds and yeasts
are destroyed, except for a few rare, heat-resistant species.
Yeasts are another type of fungi. They act upon starches and
sugars to produce alcohol and carbon dioxide in the process of
fermentation. The ability of yeasts to bring about fermentation
makes them very valuable organisms for the production of bread,
beer, and wine. But they can cause food to ferment even when it
is not desired, making the food unfit for consumption. This type
of food spoilage can be prevented by reducing the moisture content
of the food and raising or lowering the temperature beyond
the point required for yeast growth.
Bacteria are microscopic organisms that exist almost everywhere.
Some bacteria are beneficial in that they help in the production
of certain foods. For example, cheeses are made by the action of
certain bacteria on milk. Yet others are harmful because they
contribute to food spoilage or produce poisons that can cause
serious illness and even death when ingested.
Some spoilage-causing bacteria can be killed at the same temperatures
that destroy yeasts and molds. Others must be heated to
temperatures as high as 116[degrees]C (240[degrees]F) for as long as 20 minutes.
Keep in mind that cooking time lengthened as altitude increases.
Where food preservation is concerned, the most dangerous of all
bacteria is the one that causes botulism, a disease that is often
fatal. Botulism-causing bacteria are naturally found in the soil.
They thrive at moderate temperatures between 21[degrees] and 43[degrees]C (70[degrees]
and 120[degrees]F) and can be easily introduced into food through contaminated
utensils, soiled hands, or polluted water.
Botulism-causing bacteria can be destroyed by heat at temperatures
above boiling, at least 116[degrees]C (240[degrees]F), for up to 20 minutes.
This type of bacteria can survive, grow, and reproduce only
in moist environments at room temperature, and in the absence of
air. These are the exact conditions present in cans or jars where
food is preserved by the canning process.
Properly canned food should be safe from botulism poisoning,
since both the poison and bacterium are destroyed by boiling for
15-20 minutes. But if canned food should ever smell bad when
opened, it should be discarded to avoid being eaten.
Enzymes are organic compounds classified as proteins. They function
as chemical catalysts in the cells of plants and animals
and are essential for normal growth and development. However,
after a fruit or vegetable is picked, its enzymes slowly stop
functioning in their normal constructive way and start to break
down the plant tissue. If this action is not slowed or halted,
the produce will start to decompose and eventually spoil. It is
therefore necessary to slow or stop the action of enzymes if
fruits and vegetables are to be preserved successfully.
Enzyme action requires specific environmental conditions within
the cell. These include narrow ranges of temperature, moisture,
and acidity. If any of these conditions is significantly changed,
the action of the enzyme can be altered. For example, enzyme
action slows down at lower temperatures and increases at temperatures
slightly higher than normal. Some enzymes are destroyed
when plant tissue is heated above 54[degrees]C (130[degrees]F). But many, including
some that contribute to browning of foods, may not be destroyed
at temperatures less than 90[degrees]C.
Besides temperature and moisture, two other factors affect the
actions of food spoiling agents. The first is cleanliness, the
act of working with food only under sanitary conditions. This
involves cleaning all foods thoroughly before preserving them,
keeping hands and work area clean, and washing all equipment used
in the preservation process in boiling water. If proper care is
taken to keep everything very clean, food that is preserved
should keep for many months, remaining tasty and nutritious.
The second factor in controlling food spoiling agents is the
level of acidity of the food being preserved. Many of the microorganisms
that bring about spoilage are very sensitive to acidity
and cannot live in highly acidic environments. These spoiling
agents can be controlled by increasing the acidity of the environment.
Some fruits and vegetables are naturally acidic and
therefore are easier to preserve. Foods with the acidity measurement
of 4.5 or higher are considered to be low in acid. Beans,
corn mushrooms, pumpkin, white potatoes, etc., are some examples
of common low-acid fruits and vegetables. On the other hand,
foods with acidity measure of below 4.5 are regarded as strong in
acid content. Some examples of high acid fruits and vegetables
are lemons, grapefruits, oranges, tomatoes, pineapples, etc. It
is important to remember that varieties of the same food will
have different ratings, as will identical varieties grown under
different conditions.
The major methods of fruit and vegetable preservation are canning,
pickling, drying, freezing, and curing (smoking or salting).
Whatever method of preservation you choose, keep in mind
that preserved food is only the next-best alternative to fresh
food, not a replacement. Whenever a fruit or vegetable is preserved
some of the food's nutritional value is lost, along with
some of its natural flavor, color, and aroma. For this reason,
only the freshest and best quality fruits and vegetables should
be used for preservation.
Canning is practiced in many parts of the world. Even though it
seems quite complicated at first, canning is easy once a person
becomes familiar with the process.
Canning uses heat to bring about sterilization and the exclusion
of air for preserving fruits and vegetables. Heat sterilization
destroys the microorganisms that cause spoilage or poisoning in
food. Exclusion of air forces air out of the food, thus creating
an airtight seal. Two methods are used to sterilize the food, the
water bath, and the pressure cooker. In the water bath process,
the jars of food are submerged in water in a large kettle and
allowed to boil for a specified period of time. The pressure
cooker method, which must be used for safe handling of low acid
foods, uses a pressure canner instead of a kettle to achieve the
higher temperatures that are necessary.
After freezing, canning is the most expensive home method of
preserving fruits and vegetables. However, it is one of the best
methods of preserving products that are to be stored for long
periods of time. Most of the expense involved in canning is the
initial investment in canning jars and other equipment that may
not be on hand in the home. Once all of the materials are bought,
canning becomes much less expensive, since the costs are averaged
over time. When compared to the cost of fruits and vegetables
purchased during off-season or those commercially canned, the
cost of home canning often is inexpensive.
The Principles of Canning
Only fresh, undamaged fruits and vegetables should be selected
for canning. They should be carefully trimmed, cleaned, and cut
into pieces of the desired size for preserving. The food is then
packed into jars either hot (hot packing) or raw (cold packing).
The method used depends on the type of fruit or vegetable being
preserved and the recipe being followed.
Fruits and vegetables that are fairly delicate in nature are
often packed raw because they tend to keep their shape better
with this method. After being carefully but firmly packed into
the jars, some type of boiling liquid, specified by the recipe
being followed, is poured over the produce. Firmer fruits and
most vegetables are often pre-cooked before packing (hot-packed),
since they take up less space in the jars after being cooked.
Usually, hot-packed produce has a shorter processing time than
cold-packed produce since the food has already been cooked. The
time required for pressure canning is not shortened much at all.
Regardless of which packing method is used, it is important to
leave a small amount of air space--about one to three centimeters
deep--between the food and the jar lid. It is also advisable to
cover the food completely with liquid to prevent its exposure to
the air, which may discolor it.
Water Bath Process. If the cold pack, or water-bath, canning
method is being used, the packed jars, with their tops put in
place but not sealed tightly, are placed on a shallow rack in a
large pan filled with warm water (never place cool jars in boiling
water or they may break). Add enough water to completely
cover the jars of food by at least three to five centimeters. As
the water in the water-bath boils, any air in the jars or food
will be expelled. This helps to create a vacuum, thus enabling
the jars to seal tightly.
After the appropriate processing time, the jars are allowed to
cool for a minute or two in the water. They are then lifted out
of the hot water and dipped into cold water. Dipping secures the
seal by increasing the vacuum.
When the jars are completely cool, they are labeled with the name
of the produce and the date canned, and carefully stored away in
a cool (between 4 and 21[degrees]C or between 40 and 70[degrees]F), dark place to
retard the loss of nutrients.
Pressure Process. To process low acid fruits and most vegetables,
it is necessary to use a pressure canner instead of a water-bath
canner. Read carefully any canning instructions provided by the
manufacturer of the pressure canner being used. First, pour water
into the pressure canner to a depth of about four centimeters.
Next, carefully place the jars on the rack and seal the pressure
canner. Heat the pressure canner on a cookstove for several minutes,
until steam leaves the vent at the top of the pressure
canner's cover. Then fix the weighted gauge over the vent.
After the appropriate cooking time for the food being processed,
let the pressure canner cool until the inside pressure, indicated
by the gauge, falls to zero. Then gently raise the gauge slightly
off the vent to release excess steam from the pressure canner.
Open the pressure canner by lifting the lid away from you so that
you will not be burned by any remaining hot steam.
Remove the jars, and let them cool until they can be touched.
Then carefully place them in cold water to complete the sealing
process. Finally, label the jars and store as described earlier.
Equipment and Materials Required
Much of the equipment required to can fruits and vegetables may
already be present in many homes. The amount of equipment to be
purchased depends upon how much canning will be done and what
fruits and vegetables will be preserved. The following is a list
of basic equipment often needed to can fruits and vegetables:
o     A large tall cooking pot for water-bath canning (See Figure 1).

udc1x6y.gif (437x437)

      The pot should be either stainless steel or an
      enameled metal.
      Aluminum or iron
      pots will corrode
      when they come in
      contact with the
      acidic juices from
      fruits and vegetables.
      The pot
      should also be
      7.5 to 12.5 centimeters
      deeper than
      the jars used to
      contain the food.
o     A pressure cooker or pressure canner (see Figure 2) for

udc2x6y.gif (437x437)

      canning low-acid foods. This should be large enough to
      hold at least four
      quart jars. Although
      a large
      pressure cooker
      can be used, canning
      recommend using a
      pressure canner
      since it is designed
      and constructed
      for canning.
o     Jars that are in very good condition with tight-fitting
      lids and seals.
o     Cheese cloth or a wire basket to hold food for straining
      and blanching (dunking fruits and vegetables in boiling
      water or exposing them to steam).
o     Large spoons and a ladle, made of wood or stainless steel,
      and a selection of knives and smaller cooking pots.
o     A wide-mouthed funnel for filling jars.
o     Something with which to lift jars out of the cooking pot
      or pressure canner (special tongs may sometimes be available).
o     Measuring spoons and cups, and a timer.
In addition to this equipment, some type of cookstove will be
needed to heat the water-bath canning pot or pressure canner.
The Pressure Canner. The most expensive piece of equipment aside
from the cookstove is the pressure cooker or pressure canner.
Whether or not this is needed will depend upon the acidity of the
fruits or vegetables to be canned. The pressure cooker is required
for low-acid foods (all vegetables except tomatoes), but
it is not necessary if only high-acid foods such as tomatoes and
most fruits are to be canned.
The pressure canner is the only type of cooking device that can
destroy the bacteria spores responsible for producing botulism
poison. The pressure canner pressurizes the boiling water, allowing
the temperature of the steam inside to reach temperatures as
high as 121[degrees]C (250[degrees]F). Because of the high pressure and temperature
produced by the pressure canner, it is very important to
follow the manufacturer's instructions carefully and keep the
vent and safety valve unclogged and clean.
The Jars. Special care also needs to be taken in the selection of
canning jars, since faulty jars may lead to spoilage of the preserved
food. If possible, jars made specifically for home canning
should be used. The cost of the jars could be expensive, but when
averaged over the many years that they can be used, their relative
cost becomes much lower. Most beginning canners may find it
necessary to start with a relatively small number of jars the
first year and then add more jars each successive year. This will
help reduce initial expense and make the first year's work a
little easier.
Most canning experts advise against using jars that have previously
been used to store commercially canned produce. According
to these experts, such jars are designed to be used only once and
are not as sturdy or well made as jars manufactured specifically
for home canning. In addition, commercial canning jars are often
difficult to reseal once the jars have been opened. This leads to
contamination and spoilage of the canned produce. Commercial jars
can be used for some applications, such as the canning of jams
and jellies, since they are used only as containers and do not
play a critical role in the preservation process.
Three general types of jars are made specifically for home canning:
a jar with porcelain-lined zinc cap and rubber ring closure;
a jar with a screw band and self-sealing lid; and a jar with
glass lid, rubber ring, and wire-clamp fastener. Examples of
these jars are shown in Figure 3. All canning jars have the advantage

udc3x8.gif (393x486)

of being usable over and over again. Only the rubber
seal or self-sealing lid needs to be replaced after each use.
Labor Requirements
Canning is not overly complicated, but it requires careful planning
and execution if it is to be successful. Since it is best to
can only fresh, undamaged fruits and vegetables, canning needs to
be done during peak harvest times, when a sufficient supply of
produce is available. The number of workers and the amount of
time needed to process the produce depend upon the quantity of
fruits and vegetables that can be processed. Generally, home
canning can be accomplished by as few as one or two people, and
each canning session may last from four hours to all day. Canning
time also depends upon the number of jars of produce that can be
processed by either the pressure canner or the water-bath canner
at each heating; a larger canner permits the processing of more
jars at one time. To keep the time required for canning to a
minimum, it is important to make sure that all the equipment and
materials needed are clean and ready for use.
Remember that water-bath canning time lengthens as altitude increases.
Therefore it is important to adjust cooking time with
altitude changes.
Energy Requirements
Canning is second only to freezing in terms of the quantity of
commercial energy required, but this amount is relatively small.
Although it is possible to heat both the pressure canner and the
water-bath canner over a wood fire, it is much more convenient to
use kerosene, gas, or electricity, and the amount of heat generated
is much more easily controlled.
There are essentially three steps in the canning process that
require energy use. The first is the cleaning of the canning
equipment, jars, lids, and seals with scalding water. Depending
on the recipe being followed, some fruits and vegetables will
also need to be blanched (dipped in boiling water for a short
period of time to retard or stop the destructive action of enzymes)
or precooked before they can be processed. This is the
second step of the canning process that requires the use of energy.
Finally, all produce must be processed in either a pressure
canner or water-bath canner. The quantity of energy used in each
of these steps depends primarily upon the amount of produce being
To determine whether canning is an economically viable method of
preserving produce for a specific family, it is necessary to
compare the costs and benefits of canning against other alternatives.
For example, it is important to compare the costs of canned
produce with the average yearly cost of fresh produce. When
doing this, it is also helpful to spread the cost of the equipment,
jars, and other utensils over several years, not just the
year of purchase or for a single year of canning. Most of this
equipment can be used year after year, and usually for more than
just canning. This makes canning less expensive.
Generally, fruits and vegetables are least expensive and most
readily available during peak harvest, which is not only the best
time to eat fresh produce, but the best time to preserve it for
later use. Preserved produce has its greatest value during the
off-season when fresh fruits and vegetables are either not
available or are very expensive.
Another important consideration is the cost involved in the loss
of fruits and vegetables due to spoilage. People who have gardens
often harvest more than they can either consume or sell.
Preserving this surplus is likely to be more economical than
letting it spoil. In addition, having a variety of canned fruits
and vegetables on hand for year-round consumption adds diversity
to meals, and improves a family's diet. The economic advantage
of a better diet may be difficult to estimate, but it should be
obvious to everyone.
It is also important to compare the cost of home-canned produce
to that of commercially canned produce. When making this comparison,
it is important to consider not only the price difference
but also the probable difference in quality. Home-canned produce
is often of higher quality and superior flavor than commercially
canned food. In addition, if you are considering home-scale canning,
you need to weigh the costs and benefits of this method
against other preservation methods for home use.
Finally, you should consider the value of your time. Is canning
your own food the best way to spend your time, especially if you
must also work full time at a job, in the fields, or elsewhere?
You may not have choice--preserving your own foods may be the
only way to assure an adequate diet for your family in the off
season. But your time is important, and it should be calculated.
Advantages and Disadvantages
The advantages and disadvantages of home-scale canning depend
upon the type of produce being preserved, the conditions of the
specific locality, and the skills and resources of the people who
will be doing the work. There are some general points, however,
that should be considered. Canning, like all preservation methods,
prevents the unnecessary loss of food due to spoilage. This
enables people to eat specific fruits and vegetables year-round,
thus improving the character and quality of their diets. Canned
produce is easy to store, and it also retains much of the natural
flavor, color, and nutritional value of the fruit or vegetable.
One of the biggest advantages of canning over other preservation
methods is that at meal time canned produce is quick and easy to
prepare since it has already been cleaned, cut, and in many cases
cooked. Properly canned food also has a shelf life ranging from
six months to several years, depending on the type of food.
On the other hand, canned produce, like all preserved produce,
suffers some loss of vitamins and other nutrients. But the loss
of only a small portion of the nutritional value of a food is of
little consequence when compared to not having any of the food or
nutrients available at all.
The biggest disadvantage of canning is the high initial cost of
all the equipment needed to start a home-scale canning operation.
This may prohibit some people from using this technique. An additional
disadvantage for some people may be the difficulty of
acquiring the pressure cooker or pressure canner that is needed
to can low-acid foods. The special jars needed to can properly on
the home-scale may also be difficult to acquire in some areas.
The energy demands of canning may also prove to be a disadvantage
to some, and therefore a less energy-intensive preservation method
may need to be chosen.
Maintenance Requirements
Little more than cleaning is needed to maintain a good canning
operation, but the value of this cannot be overstressed. The
cleaner the equipment, jars, produce, kitchen, and work surfaces,
the better the results. The old saying, "An ounce of prevention
is worth a pound of cure," is very appropriate for successful
Since the jars are one of the most important parts of the entire
canning process, they should be examined very carefully before
being used. Any chipped or damaged jars should be discarded along
with any imperfect rubber rings or lids. A defective jar, lid, or
seal could lead to contamination and spoilage, and even botulism
poisoning. If a pressure canner is used, it is very important to
follow the maintenance instructions provided by the manufacturer.
Variations and Alternatives to Home-Scale Canning
One possible way to overcome the problems of high initial cost is
to establish a cooperative canning center. Through a cooperative
effort, a group of people could combine their financial resources
to purchase a large water-bath canner and pressure canner, as
well as other utensils. This may result in significant savings.
Also, if enough people are involved in the cooperative canning
center, the cost of the jars may be reduced by buying in large
Communities that already have agricultural cooperatives will
probably have little difficulty getting such a community canning
center started. Before this type of cooperative can be established,
however, it is important to address some basic questions.
First, are there enough people in the community interested in
canning fruits and vegetables? Second, is there a building available
for such a cooperative to use? Since canning is generally a
seasonal activity, there is no need to have a permanently-established
kitchen. Third, is there someone in the community with the
skills to supervise the activities of the cooperative and keep
the necessary financial records? If positive answers to these
questions can be found, there is a good chance that a cooperative
canning kitchen could be established.
Freezing involves lowering the food temperature below the freezing
point of water (0[degrees]C or 32[degrees]F). For the initial freezing of
fruits or vegetables, it is important to lower the temperature
of the produce to between -15[degrees]-20[degrees]C (-5[degrees] -0[degrees]F) as quickly as possible.
For quicker freezing, fruits and vegetables should be
spread out individually on trays in the freezer so air can circulate
freely. The more rapid the freezing process, the fresher
tasting the final product. Once the food is frozen, it should be
packaged and then stored at about -20[degrees]C (0[degrees]F).
Generally, fruits and vegetables are each prepared differently
for freezing, but in all cases, only fresh, undamaged produce
should be selected for freezing.
Equipment Needed
Freezing fruits and vegetables requires equipment such as a
freezer or access to frozen food cooler, food containers (jars,
plastic boxes, heavy plastic bags), waxed paper boxes, blanching
kettle, strainers, a timer, etc.
Freezing Fruits
Fruits are usually not blanched or cooked before they are frozen
to allow them to retain their garden-fresh flavor. Fruits such as
peaches are an exception to this rule because their peels are
much easier to remove after blanching.
There are two basic ways to pack fruits. The first and simplest
is the dry pack method: the fruit is just put whole or cut and
peeled into containers and then placed in the freezer. In some
cases, it is better if the fruit is allowed to freeze first before
it is packed so that it will not stick together in the container.
The advantage of this packing method is that the fruit
can be used a little time.
The second way to pack fruits, and probably the preferable way
for most fruits, is the wet pack method in which the fruit is
packed along with some liquid, usually sweetened. For fruits that
are naturally juicy, all that may be needed is to add some sugar.
The sugar not only sweetens the fruits but draws out their natural
juices, which results in the formation of a sweet syrup. After
all the sugar is dissolved, the fruit can be packed and frozen.
Other fruits can be frozen after a cold sugar syrup is poured
over the packed fruit. Plain fruit juice and water can be used in
place of a sugar syrup if the extra sweetening is not desired.
Freezing Vegetables
Vegetables, like fruits, are prepared for freezing by cleaning,
cutting, and peeling. Unlike most fruits, however, vegetables
must be blanched in boiling water for a few moments and then
quickly dunked in very cold water. Blanching maintains quality
and slows enzyme activity. It also softens the vegetables, making
them easier to pack. Before packing and freezing, they should be
thoroughly drained. If wet vegetables are placed in the freezer,
they stick together and frost will form in the container. Most
vegetables are packed in containers without adding anything
extra. This allows them to be used as if they were fresh produce.
Care of Frozen Food
It is important to remember that unfrozen food should not be
piled together in the freezer. Instead it should be spread out
along shelves so that it will freeze as quickly as possible. All
packaged fruits and vegetables should be carefully labeled with
the amount of produce, the name of the fruit or vegetable, and
the date. Labeling makes it easier to identify the contents of
each package. Finally, food stored in the freezer should be rotated
so that the oldest food is eaten first. This will prevent
food from being held in the freezer for too long. Dating packages
ensures that the oldest frozen produce will be used first. Note
that frozen produce generally has a maximum storage life of one
year. Longer storage will not make foods unfit for use, but may
reduce quality.
As a general rule, foods that have been completely thawed should
not be refrozen because they may become sources of food poisoning
and because quality is reduced. More information about the freezing
requirements for varieties of fruits and vegetables can be
found in many guide books on food preservation.
Labor Requirements
As noted, freezing is the simplest, quickest, and easiest method
of preserving fruits and vegetables. Home-scale freezing can
easily be done by one person, although two or three people can of
course be involved. The fact that only small batches of fresh
produce are frozen at any one time makes the job less tiring.
Energy Requirements
The amount of electricity required to operate a freezer depends
upon the model and age of the freezer, its usage, and the outside
temperature. Usually, a freezer is a fairly expensive piece of
equipment to own. Energy use can be slightly reduced by keeping
the freezer as full as possible (jugs of water can be used to
occupy spaces not taken (up by food) and opening the door as infrequently
as possible.  Freezers that keep frost from accumulating,
i.e., frost-free freezers, use more energy than regular-freezers,
if the regular freezer is periodically defrosted.
The only other stage in the freezing process that uses energy is
the blanching of vegetables. If the produce is well prepared in
advance, energy use can be kept to a minimum.
The main expenses associated with freezing are the initial cost
of the freezer and the daily cost of the energy needed to keep it
running. Both of these costs may equal the value of the time
saved in the preparation of the produce for freezing, along with
the ease of preparing the frozen food for the table. If the costs
of the freezer and electricity run second to the value of the
time and energy required to prepare produce for preservation, and
the character of the preserved fruits and vegetables is of prime
concern, freezing may be the best method.
Finally, the Asian Institute of Technology in Bangkok, Thailand,
has developed an experimental freezing unit that runs on solar
energy instead of electricity. At present, this system is much
too large and expensive to be used in the home. It is probable,
however, that inexpensive home-scale solar-powered freezers will
be developed in the future.
Advantages and Disadvantages
The major advantage of frozen produce is that it retains much of
its original fresh flavor, color, and nutrients. It is also quick
and easy, requiring little preparation, and the final product is
superior to other produce preserved using other methods. On the
other hand, the disadvantage is the cost involved in the purchase
and operation of the freezer. Another disadvantage is having to
deal with a freezer full of thawing food in the event of a power
outage or freezer failure.
Maintenance Requirements
Except for cleaning the equipment used to prepare the produce for
freezing, there is little regular maintenance. If the freezer is
not self-defrosting, it must be periodically defrosted. Defrosting
is necessary for two reasons. First, as frost builds up it
takes up valuable space in the freezer that could have been used
to freeze fruits and vegetables. Second, frost build-up reduces
the cooling efficiency of the freezer. Regardless of what type of
freezer you own, it is important to follow maintenance suggestions
provided by the manufacturer of the freezer.
Alternatives to Home Freezing
In some situations, it may be possible to rent storage space in a
large commercial frozen food locker instead of buying a freezer.
This may be a good way for people to become familiar with the
freezing method before actually committing themselves to an expensive
piece of equipment. However, a disadvantage of renting
freezer space outside the home is the added difficulty of having
to transport the prepared fruits and vegetables to the freezer
and then bring them back home when they are needed.
It is unlikely that only one of the four preservation techniques
--canning, freezing, drying, or curing--would be the only suitable
method. Therefore, a food preparation system should be developed
that matches your particular situation. Such a system
should consist of a combination of methods that are appropriate
for the different types of fruits and vegetables to be preserved.
It should also meet the available resources and the specific
needs of the individuals involved.
The two most dominant constraints affecting the type of preservation
system that can be used are the availability of capital
and the cost and availability of a constant supply of commercial
energy. These constraints essentially group the four different
preservation methods into three primary systems:
1.  Where commercial energy and money are readily available,
    system one, comprising all four methods, can be used.
2.  Where sufficient energy but only a moderate supply of
    money are available, system two, comprising canning, drying,
    and curing, can be used.
3.  Where energy is either lacking or very expensive, and
    money is in short, supply, system three, comprising
    drying and curing, can be used.
Secondary constraints are also important for determining which
preservation method or methods can be used. For example, the
following questions should be addressed in deciding which of the
four methods or system to use. The brief discussion following
each question points out many factors that must be considered
before a decision can be reached.
o  How long will the food need to be preserved? If relatively
   short-term preservation is desired (six months to a year),
   and easy preparation is an important concern, then freezing
   may be the best choice.
o  How much food needs to be preserved? If only a relatively
   small amount of food needs to be preserved, then freezing
   may be the best choice. On the other hand, if quantities
   to be preserved are larger than available freezer space,
   canning, drying, and/or smoking may be better choices.
o  Are the proper jars for canning available along with other
   necessary equipment? If so, and large quantities of food
   need to be preserved, then canning may be the best choice.
o  What fruits and vegetables need to be preserved? Some
   fruits and vegetables respond better to specific preservation
   methods. Some may turn to mush if frozen; canning may
   have the same effect on others. To decide which method or
   methods would be most suitable for a specific vegetable,
   it is best to consult one of the books listed in the bibliography,
   or seek help from the government agricultural
   office, a high school, or a university.
o  Is a special or unique taste treat desired? If so, then
   canning or pickling may be better choices, since both are
   used to make specialty foods.
o  How much previous experience with food preservation do you
   have? If the answer is little or no previous experience,
   then maybe the least complicated method should be tried
   first. It is a good idea to master this method before
   advancing to more complicated and difficult procedures.
o  What is the weather like during peak harvest time? If it
   is sunny, dry, and windy, then preserving with a solar
   dryer may be a good choice, provided it also meets all
   other preservation requirements.
o  How many people are available to help with a large quantity
   of fruits and vegetables? If only one or two family
   members will be involved in food preservation, it might be
   best to select a method, like freezing or curing, that can
   be done in the shortest amount of time with the fewest
   number of people.
o  Which preservation method do you like best? Trying out
   different methods on a variety of fruits and vegetables
   will enable you to develop your own preferences. At this
   point, it is important to note that determining a preservation
   method requires careful consideration of many
   variables that make up a situation. In most cases, though,
   there is a significant amount of leeway open to the individual
   in selecting the appropriate preservation method.
Anderson, Jean. The Green Thumb Preserving Guide.   New York:
  William Marrow & Company, Inc., 1976.
Barbour, Beverly.  The Complete Food Preservation Book.  New York:
  David McKay Company, Inc., 1978.
Burch, Joan, and Burch, Monte. Home Canning and Preserving.
  Reston, Virginia: Reston Publishing Company, Inc., 1977.
Central Food Technological Research Institute. "Home-Scale
  Processing and Preservation of Fruits and Vegetables."
  Mysore, India: The Wesley Press, 1981.
Hertzberg, Ruth; Vaughan, Beatrice; and Greene, Janet. Putting
  Food By. Brattleboro, Vermont: The Stephen Greene Press.
Kluger, Marilyn. Preserving Summer's Bounty. New York: M. Evans
  and Company, Inc., 1978.
Levinson, Leonard Louis. The Complete Book of Pickles and
Relishes. New York: Hawthorn Books, Inc., 1965.
Schuler, Stanley, and Schuler, Elizabeth Meriwether. Preserving
  the Fruits of the Earth New York: The Dial Press, 1973.
Stoner, Carol Hupping, Editor. Stocking Up: How To Preserve the
  Foods You Grow, Naturally. Emmaus, Pennsylvania: Rodale Press,
Groppe, Christine C., and York, George K. "Pickles, Relishes, and
  Chutneys: Quick, Easy, and Safe Recipes." Leaflet No. 2275.
  Berkeley, California: University of California, Division of
  Agricultural Sciences, 1975.
Etchells, John L., and Jones, Ivan D. "Preservation of Vegetables
  by Salting or Brining." Farmers' Bulletin No. 1932.
  Washington, D.C.: U.S. Department of Agriculture, 1944.
Worgan, J.T. "Canning and Bottling as Methods of Food Preservation
  in Developing Countries." Appropriate Technology. 4
  (November 1977): 15-16.
Islam, Meherunnesa. Food Preservation in Bangladesh. Dacca,
  Bangladesh: Women's Development Programme, UNICEF/DACCA, 1977.
Stiebeling, Jazel K. "Solar Food Preservation." Chicago,
  Illinois: Illinois Institute of Technology, 1981.
U. S. Department of Agriculture. Human Nutrition Research
  Division. "Home Canning of Fruits and Vegetables."
  Washington, D.C.: U.S. Department of Agriculture, 1965.
Dixie Canner Equipment Company
786 East Broad Street
P.O. Box 1348
Athens, Georgia 30601 USA
(Can Sealers)
Food Preservation Systems
P. O. Box 188
New Windsor, Maryland 21776 USA
(Canning Equipment)
Freund Can Company
155 West 84th Street
Chicago, Illinois 60620 USA
(Cans and Sealers)
National Presto Industries
Eau Claire, Wisconsin 54701 USA
(Pressure Canners)
Refrigeration Engineering Corporation
8799 Crownhill
P. O. Box 3-C
San Antonio, Texas 78217 USA