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                             TECHNICAL PAPER # 60
                           UNDERSTANDING HOME-SCALE
                             PRESERVATION OF FRUITS
                               AND VEGETABLES
                                   PART II
                              DRYING AND CURING
                                 Eric Rusten
                             Technical Reviewers
                               Joel M. Jackson
                                 George Rubin
                              George G. Schultz
                                 Published by
                       1600 Wilson Boulevard, Suite 500
                         Arlington, Virginia 22209 USA
                     Tel. 703/276-1800 . Fax: 703/243-1865
                   Understanding Home-Scale Preservation of
                             Fruits and Vegetables
                          Part II. Drying and Curing
                             ISBN: 0-86619-279-4
                [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
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 as possible.
This paper, the second of a two-part series, discusses principles
of drying and curing (smoking or salting) fruits and vegetables
at home, for home use. The preceding paper looked at the principles
of canning and freezing. 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 a temperature of 90[degrees]C or more, all molds and
yeasts are destroyed, except for a few rare, heat-resistant
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 heating them to
temperatures above boiling, at least 116[degrees]C (240[degrees]F), for up to 20
minutes. It is important to note that 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 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 measurement 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.
Drying fruits and vegetables to retard or prevent spoilage has
been practiced in many parts of the world for thousands of years.
Sometimes known as sun drying, this process involves laying produce
out in the sun until it becomes suitably dry, and then storing
it in containers for later use.
The basic principle behind drying fruits and vegetables is to
remove between 80 to 90 percent of the water from the produce,
thereby creating an environment that cannot support microbial
life. Also, as water is removed from the plant's tissues, salt,
sugar, protein, and other solutes increase in concentration. This
is an additional factor that prevents the growth and reproduction
of microorganisms that may cause spoilage.
Several factors are important when considering drying as a possible
method for preserving fruits and vegetables.
o     Dried fruits and vegetables taste different from fresh,
      canned, or frozen produce, even when they are reconstituted
      by adding water before they are eaten. People who are
      not in the habit of eating dried produce may need some
      time to get used to the different tastes.
o     Exposing fruits and vegetables to sunlight and heat will
      result in the loss of some vitamins. The longer the
      exposure time, the greater the loss of nutrients. This
      partial loss of vitamins from the produce can be reduced
      through careful pretreatment before drying and during the
      drying process.
o     The various nutrients in dried produce are highly concentrated
      because of the removal of most water from the
      tissues of a fruit or vegetable. In other words, 500 grams
      of fresh apples will have less nutritive content than 500
      grams of dried apples.
o     Some fruits and vegetables are easier to dry than others.
      For example, apples, apricots, coconuts, dates, figs,
      guavas, and plums are fruits that dry quite easily, while
      avocados, bananas, breadfruit, and grapes are more difficult
      to dry. Most legumes are easily dried, as well as
      chilies, corn, potatoes, cassava root, onion flakes, and
      the leaves of various herbs and spices. On the other
      hand, asparagus, beets, broccoli, carrots, celery, various
      greens, pumpkin, squash, and tomatoes are more difficult
      to dry successfully. If done with the help of solar energy,
      the drying of fruits and vegetables is the least
      expensive of food preservation methods.
o     Produce that has been dried sufficiently and stored in
      airtight containers stays fresh for about six months to a
      year, depending on the storage containers used and the
      type of produce preserved.
Methods of Drying
There are essentially three different ways to dry fruits and
vegetables. First and most basic is simple sun drying, where
produce is simply laid out in the sun to be dried. There is no
pretreatment, and no special devices are used to assist the drying
process. The second method, solar drying, again makes use of
the sun's energy to help dry the fruits or vegetables. However in
this method, the produce is usually pretreated to prevent discoloration
and retard vitamin decomposition, and housed in a
special structure to aid the drying process. In the third method,
the produce is pretreated, and placed in a special drying device
that uses commercial energy as its source of heat. All of these
methods, although similar in some respects, do require slightly
different materials and equipment, and therefore each will be
treated separately.
Sun Drying. To sun-dry fruits and vegetables, you need a clean,
flat surface, plenty of sunlight, and warm, dry air. This method
has been used for thousands of years. But there are several drawbacks.
First, it takes a significant amount of time to completely
dry the fruit or vegetables. Second, while the produce is drying,
it is exposed to airborne pollutants so that the final produce
will most likely not be very clean.
Solar Drying. On the other hand, solar drying overcomes these
difficulties by placing the prepared produce on trays made of
non-metal material, and then placing the trays in a structure
covered with glass or plastic. An example of a simple solar dryer
is shown in Figure 1. Since a solar dryer depends upon sunlight,

udc1x6z.gif (600x600)

it costs essentially nothing to operate. However, solar dryers
can be used only when sunlight is intense and the air relatively
dry. Depending upon the types of fruits and vegetables being
dried and the temperature and humidity of the air, it can take
from one to three days to completely dry produce.
Convection Drying. Both of these problems--the need for sunlight
and the slow drying time--can be overcome by using a convection
dryer, which does not depend on sunlight to dry the produce. By
using a commercial source of energy such as electricity, gas, or
kerosene, the amount of heat entering the dryer can be closely
regulated and maintained at an optimum level (30-60[degrees]C or 86-140[degrees]F),
thereby keeping drying time to a minimum. Moreover, since
fruits and vegetables are not exposed to sunlight during the
drying process, they retain more of their vitamins. A low-cost,
kerosene-heated dryer is shown in Figure 2. One of the disadvantages

udc2x6z.gif (600x600)

of drying produce in a convection dryer is the high cost
of the energy required to operate the dryer.
Each of the preceding methods requires that the fruits and vegetables
undergo some form of preparation before being dried.
The equipment and materials needed to prepare produce depend
partially on the type of produce being processed, but primarily
on whether pretreatment against discoloration, vitamin loss, and
contamination is carried out. If the produce needs only to be
dried so that it can be stored for a few months and the color of
the dried fruit is of little concern, very little equipment will
be needed other than knives to slice and peel the produce.
On the other hand, if you want to store dried produce longer than
one or two months, and you also want to prevent discoloration and
retard vitamin loss while the produce is being dried, more equipment
and materials will be needed. Such equipment includes:
o     A medium to large cooking pot (between 4 and 8 liters in
      volume) in which to blanch the produce if needed;
o     A large basin or plastic bucket (about 10 to 20 liters in
      volume) in which to soak the produce in an anti-discoloration
o     Another large basin or plastic bucket in which to soak the
      produce in a sulfite solution to combat vitamin loss and
o     A wooden fume box in which to sulfurize the produce, if a
      better treatment method against vitamin loss is desired;
o     Some sublimed sulfur (99.5 percent pure) or a powdered
      sulfite compound such as sodium bisulfite or potassium
      metabisulfite, if the produce will be sulfurized. However,
      sulfite has been found to cause allergic reactions in a
      small percentage of people and should be used with care.
o     Some ascorbic acid (vitamin C) or lemon juice to make the
      anti-discoloration solution, if the produce will be pre-treated
      against discoloration.
o     Storage containers (glass jars with tight-fitting lids
      work best; sturdy plastic bags also work well).
It is not difficult to construct a fruit and vegetable dryer, but
care must be taken in selecting the construction materials. Be
sure to choose a wood that will not discolor the produce or impart
an off flavor to it. A local carpenter could probably advise
on most suitable woods. In addition, it is important never to use
any metal materials for dryer parts that will come in contact
with the fruits or vegetables. The acidic juices from some fruits
and vegetables will corrode many metals, resulting in the probable
loss of the produce being processed and the slow deterioration
of some dryer parts.
The Drying Process
For most fruits and vegetables, drying is accomplished by increasing
the air temperature to between 33[degrees]C and 60[degrees]C (91[degrees]F-140[degrees]F),
to stimulate evaporation. This temperature is also the
ideal temperature for the growth and reproduction of many spoilage-causing
microorganisms. As a result, both spoilage and loss
of vitamins may occur. To avoid this, it is essential to dry the
produce as quickly as possible.
The rate at which fruits and vegetables dry depends on three
major factors. First, drying time is lengthened if the produce
has a very high water content, a small surface area, or a waterproof
skin. Second, drying time is increased if the relative
humidity of the air is high. In other words, if the air already
holds nearly all the water it possibly can, it will be unable to
take on much more, and the fruit will not be able to lose enough
moisture to become dehydrated. Third, as water evaporates from a
piece of fruit or vegetable, the air surrounding the food becomes
saturated with water, causing the rate of evaporation to slow
down and eventually stop. To prevent this from happening and to
keep the rate of evaporation as high as possible, it is essential
that air be kept in constant motion near the fruit to carry away
the moisture-laden air. so, to increase the rate at which fruits
and vegetables dry, force warm, dry air over produce being prepared
to enhance the evaporation of water.
As with other preservation methods, it is essential to dry only
fresh, undamaged fruits and vegetables. Following this rule will
reduce the chances of spoilage during drying and storage. After
the best produce is selected, it must be cleaned thoroughly and
in most cases sliced, peeled, and cored, if necessary. Water lost
from produce during drying causes the produce to shrink significantly.
As a result, most fruits and many vegetables should not
be sliced too thinly. The best procedure for each type of fruit
or vegetable can be determined either by the trial-and-error
method, or better yet, by following drying instructions for the
specific fruit or vegetable as outlined in a drying guide book.
Pre-Treatment. Before placing fruits or vegetables on drying
trays, you may want to preheat them. In general, fruits and vegetables
make a better product if they undergo one or more of the
following pre-drying treatments: anti-discoloration, dewaxing, or
sulfurization. Choice of pretreatment method, if any, depends on
whether the benefits outweigh the costs.
The flesh of many fruits and vegetables turns a rusty, brown
color when exposed to air. To prevent sliced produce from discoloring
during drying, you need to soak the produce in an anti--discoloration
solution. This solution can be prepared either by
dissolving one to three teaspoons of pure ascorbic acid (vitamin
C) in about one cup of water, or by squeezing the juice from
several lemons into a cup of water. The amount of ascorbic acid
or the number of lemons needed for a specific type of fruit or
vegetable can be determined by trial-and-error. This solution
should then be sprinkled over the produce soon after it has been
peeled, pitted, and sliced. An alternative method is to pour this
concentrate into a shallow basin half-filled with water. The
produce can then be soaked in the solution.
The skins of some fruits such as cherries, figs, grapes, prunes,
and other berries are not only relatively tough, they are also
covered by a thin wax-like coating that inhibits drying. If the
skins are not weakened and their wax coatings removed, the drying
rate will be significantly retarded. Both of these problems can
be solved by quickly dunking the fruit first in boiling water,
then in cold water.
The final pretreatment process is sulfurization. Pretreating
fruits and vegetables with sulfur preserves their color. In
addition, it helps retain vitamins A, B1, and C and inhibits the
growth of microorganisms in the produce during the initial stages
of the drying process. Note, however, that sulfurization is optional,
since food safety depends mainly on how successfully the
produce is dried. There are two ways to sulfurize produce. The
first method, which is relatively easy and quick, involves soaking
the prepared fruit in a sulfite solution. To make the solution,
add between 1.5 and 3.5 teaspoons (about 5-10 grams) of
sodium sulfite, sodium bisulfite, or potassium metabisulfite to
four liters of water. Then, soak the produce in the solution for
about 15 to 30 minutes.
The second method, which involves sulfurizing produce in a fume
box (Figure 3), is considered by some experts to produce better,

udc3x9.gif (600x600)

results. In this method,
a small amount of
pure powdered sulfur---about
one teaspoon
(approximately 3 grams)
for every 500 grams of
produce--is burned in
the bottom of a large
fume box containing
stacked trays of fruits
and vegetables. Once
the sulfur has completely
burned, both
vent holes in the box
should be sealed.
The produce remains inside the box for at least 20 or 30 minutes
before it is removed for drying. When removing the produce from
the box, it is a good idea to stand so that the wind blows away
from the box, thereby blowing the sulfur dioxide fumes away from
you. The trays of produce should then be loaded directly into the
dryer for drying.
Care of Dried Foods. Each fruit and vegetable has a different
appearance and texture when it is thoroughly dried. Generally, a
fruit is sufficiently dried if no moisture is visible when the
fruit is cut. Most recipe instructions for drying specific fruits
and vegetables include a test to determine whether the produce is
completely dried.
After the produce is dried, it should be left to cool (if necessary)
on the trays. Pour the dried produce into a large, open
container, preferably plastic or enameled metal. Cover the container
with a porous cloth so that air can circulate, then place
the container in a warm, dry area with good air circulation.
Leave the produce in the container for at least 10 days, stirring
at least once a day. This process, called conditioning, is done
to distribute the remaining moisture evenly in the produce, thus
reducing the chance of spoilage, particularly from mold. Freshly
dried fruits and vegetables can be added to the container, but
only during the first few days of conditioning.
After the produce is completely dried, it can be packaged and
stored. It is important to let the produce cool completely before
placing it in either plastic bags or glass jars. No special jars
are needed to store dried fruits or vegetables, but tightfitting
lids are essential if the produce is to be kept in good condition
for any length of time.
Labor Requirements
The complete process of drying fruits and vegetables can be divided
into two major activities: (1) produce preparation and
pretreatment, and (2) drying. Produce preparation and pretreatment
is more labor-intensive, but it can be done by one or two
people, if only a moderate amount of produce (10-50 kilograms) is
processed. To reduce the amount of time and effort involved in
this activity, all equipment and materials must be cleaned before
the preparation and pretreatment of the produce begin. Since
several stages in this activity involve letting the fruit or
vegetables either soak in a solution or sit on a tray, it would
be possible to set up an assembly line preparation system, if
sufficient personnel and drying space were available. This would
make the best use of the equipment and time available, and would
enable a large amount of produce to be processed in a relatively
short period of time.
Once the produce is in the dryer, relatively little work needs to
be done, except to clean all the preparation equipment. If the
produce is being dried with a solar dryer, it may be necessary to
periodically adjust the placement of the dryer to take advantage
of the sun's position. If a convection dryer is used, it may also
be necessary to periodically check the setting of the heat-producing
element. It will also be necessary to check the contents
periodically (no matter which dryer is used) to see how the drying
is progressing. It may also be necessary to shift the trays
around in the dryer so that all the produce dries evenly.
Energy Requirements
Aside from blanching (quickly heating produce in boiling water),
both sun-drying and solar dryers use no commercial energy. This
makes them not only inexpensive but useful in areas where commercial
sources of energy are either very costly or not available.
Unlike solar dryers, convection dryers do require commercial
energy. The quantity needed depends upon the amount and type of
produce being dried and the relative humidity of the surrounding
air. Generally, convection dryers either run on commercial electricity
or they are heated by means of a stove or portable heater,
using gas or kerosene. Although the temperatures required to
dry fruits and vegetables are low, a significant amount of energy
will be consumed because of the long time required to heat the
dryers. Convection dryers should probably be used only if there
is an inexpensive and reliable supply of energy available.
The principal advantage of sun-drying is that it costs nothing,
since it uses solar energy, a free, limitless energy source that
is also non-polluting. Food dried in the open, however, may be
exposed to animals and insect pests unless, it is covered with
some sort of cloth net (e.g., cheesecloth) or a fine-mesh screen.
Although no costs are associated with the operation of a solar
dryer since it also uses energy from the sun, the principal disadvantage
is the cost of either buying or building such a device.
This may be expensive initially, but since it can be used year
after year with little need for repairs or maintenance, the average
lifetime expense should be very low.
Compared to open sun-drying, solar dryers use the sun's energy
more efficiently, making it possible to dry produce in a shorter
period of time.
If a convection dryer is used, there is the added disadvantage of
having to pay for the commercial energy required to run the
dryer. Energy costs may be offset, however, because the dryer
does not require sunlight; it can be used at night or in cool,
rainy weather.
The only other probable expense, except for storage containers,
will be the purchase of chemicals required to pretreat produce.
This cost should be relatively low, however, since only small
amounts are needed to process a fairly large quantity of produce.
Advantages and Disadvantages
In general, drying fruits and vegetables is a very effective way
to preserve produce. Dried produce has the advantage of being
very light in weight and low in volume and therefore easy to
carry and store. The majority of dried fruits need no special
preparation since they can be eaten in the dried state. Also,
they are a highly concentrated source of nourishment and energy
since most of the water has been removed. Preparing dried produce
that can be eaten straight from the jar is usually a simple matter
of either adding boiling water and stirring, or cooking the
dried food until it is soft. This reconstituted produce can then
be eaten as is or mixed with other foods.
The difference in taste between fresh and dried fruits and vegetables
may be a slight disadvantage in some cases, but in most it
should not be a problem. In fact, some dried fruits may be more
flavorful than fresh fruit.
The time required to dry fruits and vegetables properly and the
resulting loss of vitamins pose two major disadvantages that need
to be carefully considered. Another important factor to consider
is the relative complexity of the pretreatment procedures involved
in preparing fruit and vegetables for drying. Some people
may also find it difficult to purchase the chemicals needed for
this stage, and some may actually find it difficult to either buy
or build a solar dryer. one final disadvantage of solar drying is
that you are at the mercy of the weather. Successful outdoor
drying is possible only in regions with prolonged sunshine and
low humidity.
Convection dryers have one major advantage over solar dryers or
sun-drying and that is, drying can be carried out around-the-clock
for days. Unlike solar dryers, convection dryers are not
subject to daily and seasonal weather variations.
But convection dryers are not without any problem. The fuels
burned in convection dryers may cause other problems. Use of wood
may contribute to problems of deforestation. Coal may cause pollution;
fossil fuels are becoming increasingly expensive and are
not always available.
Maintenance Requirements
The equipment used to dry fruits and vegetables requires little
more than simple cleaning. This maintenance task should not be
ignored since clean equipment will reduce the risk of contaminating
the produce being dried. Special care should be taken with
the cleaning of the dryer. As fruits and vegetables are processed,
their juices will undoubtedly drip onto the drying trays and
other parts of the dryer. If the trays are not cleaned after each
use, microorganisms will quickly start to grow and multiply. This
may contaminate any new produce placed on the trays. In addition,
the corrosive nature of some juices may contribute to the decomposition
of the trays and dryer.
Maintaining a solar dryer involves checking the parts periodically
for wear and tear. For example, make sure that vents are
not blocked. Plastic sheeting may need to be replaced once a year
because it scratches easily and tends to become brittle and
cloudy from prolonged exposure to sunlight. The wooden cabinet of
a homemade solar dryer will also need to be painted periodically
to prevent the wood from weathering.
If a convection dryer is used, follow the maintenance instructions
provided by the manufacturer. This will ensure that the
dryer remains in good working order for many years.
Alternatives to Home-Scale Drying
Forming a food-drying cooperative is a good way to defray the
costs of processing fruits and vegetables. Such a cooperative
could possibly have several dryers built and then work as a team
to dry everyone's surplus produce. This should allow more people
to benefit from preserving fruits and vegetables and permit the
drying of greater quantities of produce for each member.
A food-drying cooperative could easily become part of an existing
farmers' cooperative or women's organization. If successful, the
cooperative could even rent its drying services to other members
of the community, and in doing so pay for the equipment used to
prepare and dry the produce.
If surplus fruits and vegetables cannot be preserved by canning,
drying, or freezing, they most likely can be preserved by curing.
This method of food preservation uses salt (either dry or made
into a brine solution), vinegar, oils, and/or smoke to create an
environment that retards or prevents the growth of spoilage-causing
Salt is the primary ingredient used in the curing process. It has
the ability to draw water out of the food, and when used in high
concentrations inhibits the growth of many living organisms. In
small concentrations, it provides the conditions that promote the
growth and reproduction of lactic-acid-producing bacteria. As the
numbers of these bacteria increase, the amount and concentration
of the acid they produce also rise. Eventually, the level of
acidity exceeds the tolerance of not only all harmful bacteria,
but also the lactic-acid formers themselves.
Along with drying, curing is one of the oldest methods of preserving
produce. But cured produce, especially salted or brined
foods, can be preserved and stored for longer periods of time.
Although some fruits can be preserved by curing, this method is
most commonly reserved for vegetables, since the flavor of many
vegetables is fairly compatible with salt and vinegar. For this
reason, this section of the paper will refer primarily to the
curing of vegetables.
Curing is a relatively easy method of preserving produce, and
since it does not require a lot of equipment or supplies, it is
also rather inexpensive. Most cured vegetables are stored in
jars similar to those used in canning, and in some cases, the
vegetables are heated in a water-bath canner to assure their
full preservation.
Equipment and Materials Required
Since it is easier to cure relatively large quantities of produce,
it is helpful to have several large stoneware crocks or
some other large container that can hold at least 20 liters of
material and that is unaffected by the action of salt or strong
acids. Since vegetables may be soaked in a brine solution, it
will be necessary to have something to cover the vegetables with,
like a plate or a latticed wooden cover. A heavy weight will
also be needed to hold the vegetables under the brine solution.
It may also be helpful to cover the crock with a large piece of
cheesecloth to keep insects from fouling the curing solution.
Standard kitchen implements will be needed to prepare the vegetables
for processing. The following items should be kept on
hand: measuring cups and spoons, knives, a cutting board, large
spoons, large glass or enamel pans or bowls, a piece of cheesecloth
for straining, and a scale to weigh the vegetables. once
the curing process is finished, the produce will need to be
stored in jars similar to those used in canning. Some cured
vegetables also need to be boiled in a water-bath canner, so for
these you will also need a large kettle.
If the vegetables are to be smoked, it will be necessary to
either buy or build a smoke box in which the vegetables can be
hung and exposed to the thick curing smoke.
Each curing method and recipe will require different ingredients
and spices. For example, a fine-grained, iodine-free noncommercial
salt will be needed for salt curing, while vinegar with an
acid concentration of between 4 and 5 percent will be needed for
pickling, and wood and wood chips for smoking.
Curing Methods
As with all preservation methods, only fresh undamaged produce
should be used in curing.  Once selected, it should be carefully
cleaned and either left whole or cut into the desired sizes for
There are three main methods of curing produce:   salting, pickling,
and smoking.
Salting. Salting is the process of curing vegetables in salt,
which inhibits the growth and action of spoilage-causing microorganisms.
Vegetables are salt-cured in one of two ways:   by dry-salting
(salt plus juice drawn from the vegetables by the salt)
or brining (salt plus water).   The amount of natural juice in the
vegetables determines whether they need to be dry-salted or brined.
Vegetables are brined whenever they do not release enough
natural juice to form the sufficient amount of liquid required
for curing.  Vegetables with plenty of natural juices, like corn,
green snap beans, greens, or cabbage, can be dry-salted.
Vegetables such as cabbage or white turnips are often fermented
to give them a slightly sour flavor.   If you want to cure your
vegetables this way, simply use one-tenth the quantity of salt
needed for salting.  This comes to about 300 grams of salt for
each 12.5 kilograms of vegetables, although the ratio may vary
depending on the recipe being followed.   The smaller quantity of
salt stimulates the growth of the lactic-acid-producing bacteria
that not only cause fermentation but also prevents the growth and
activity of harmful bacteria.
To increase the storage life of vegetables, pack them into glass
canning jars, and boil in a water-bath canner.
Pickling. Pickling generally makes use of vinegar in place of or
along with salt to cure vegetables, although some pickle recipes
call for just brine or vegetable oil.   The procedure for pickling
is quite similar to brine-curing, with specific recipes requiring
special spices, varying quantities of vinegar or salt, and
slightly different instructions.
Smoking. Although smoking is used primarily to cure meats and
fish, it can also be used to preserve vegetables.   Smoke-cured
vegetables have a unique flavor and may be mixed with other foods
or eaten plain.  The easiest way to smoke vegetables is to slice
them if needed, tie the pieces together on a long piece of
string, and hang the vegetable braid over an open fire.   Using an
open fire is convenient only if the fire is also used to cook or
keep the house warm.  Otherwise, it would be better to build a
simple smoke box (Figure 4) for outdoor use only.

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Some vegetables need to be oiled, spiced, and slightly salted
before being smoked; others need no pretreatment.   After they are
smoked, they can be stored in cloth bags or glass jars.
You can build a simple smoke box from a barrel.   Dig the fire pit
at least 10 inches from the barrel and connect the two with a
pipe or tile trench.
Labor Requirements
Curing is one of the easiest preservation methods to perform
because it requires a small amount of time and effort.   Only one
or two people are needed to preserve a relatively large quantity
of produce.  If all the necessary materials are on hand, the
vegetables can be prepared, packed in crocks, and set aside in as
little as three to five hours, depending upon the quantity of
vegetables.  After this first stage of the process is completed,
it is necessary to examine the curing vegetables periodically and
remove any scum that may have accumulated.   Also, if the cured
produce will be kept for long periods of time, it will be necessary
to pack the vegetables in jars and process them further by
heating them in a water-bath canner.
Energy Requirements
Besides being relatively quick and easy to do, curing also uses
very little, if any, commercial energy.   In the first stage of the
salt and pickling processes, only the blanching of the vegetables
consumes any energy.  If the cured vegetables are packed in jars
and processed in a water-bath canner, a little more energy will
be needed.  Finally, if vegetables are cured by smoking, fuelwood
will be needed, but if the vegetables are hung over a fire already
being used for another purpose no additional energy will be
used.  Only a small amount of wood is needed to run a smoking box,
since only a small smoldering fire is used.   After all is considered,
curing is one of the least energy-intensive preservation
The economic advantages of curing vegetables are essentially the
same as those for other preservation methods.   However, curing
may be one of the best methods to preserve a temporary surplus of
vegetables for a few months.   The raw materials needed are usually
inexpensive and can be easily acquired, and the process is relatively
quick and easy to accomplish.   If the objective is to do
more than just cure vegetables--that is, if you want to put cured
vegetables through the canning process in the interest of extending
their storage life--the costs will rise because of the increased
energy use and the need for canning equipment and storage
Advantages and Disadvantages
Curing fruits and vegetables has four primary advantages:  it is
relatively inexpensive; it is quick; it is easy to do; and it can
turn an otherwise bland-tasting product into something more
flavorful.  In addition, it is a viable alternative for people
who may not have the money or equipment to preserve fruits and
vegetables any other way.
A major disadvantage of salt-cured vegetables is the need to wash
the salt out of them before they can be eaten.   Also, too much
salt in one's diet is not healthy, especially if other health
problems exist.  It may also be difficult or even impossible for
people living in warm tropical regions to keep the curing and
pickling crocks in a relatively cool place.
Maintenance Requirements
Because curing is a relatively simple preservation method, there
is very little maintenance required other than routine cleaning
of all equipment.  For salt and brine curing, there is the need to
periodically remove the scum from the surface of the curing crocks,
and the replacement of the covering cloth whenever it becomes
soiled.  If the cured produce is canned as necessary, jar lids
will need to be replaced as necessary, and the jars themselves
inspected for any chips or cracks.
Alternatives to Home-Scale Curing
If fruits and vegetables are to be smoked, it might be less
expensive and more convenient for a group of people to build a
smoke box that everyone could use rather than for each family to
build its own.  Additionally, some money may be saved if people
purchased supplies and materials in large quantities as a group
instead of buying smaller quantities as individuals.
Because of the vast variety of fruits and vegetables grown in any
one locality, 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 systems 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 the space available in the
      freezer, canning, drying, or curing 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
      either canning or pickling may be the best choice, 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, 1977.
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)
National Drying Machinery Co.
2705 N. Hancock Street
Philadelphia, Pennsylvania 19133 USA
(Food Dryers)
Proctor & Schwartz, Inc.
251 Gilbralter Road
Horshan, Pennsylvania 19044 USA
(Food Dryers)