Technology for Canning

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Technology for Canning

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7
Technology for Canning
*Hradesh Rajput, Deepika Goswami, Manisha Arya and
Arshdeep Randhawa
Warner Collage of Dairy Technology Sam Higginbottom
University of Agriculture Technology and Science, Allahabad, Uttar Pradesh
*Email: hrdesh802@gmail.com
Introduction
Canning is the general term applied to the process of packaging a food in a
container and subjecting it to a thermal process for the purpose of extending its
useful life. An optimal thermal process will destroy pathogenic (disease-causing)
Bacteria, kill or control spoilage organism present and have mineral impact on
the nutritional and physical quality of the food. Although we thing of canning in
term of steel or possible aluminium cans, the principle apply equally well to a
variety of food containers such as glass jar, plastic and foil laminated pouches,
semi rigid plastic tray or bowls, as well as metal cans of any one of several
shapes, including cylindrical, oval, oblong or rectangular. The concept of aseptic
packaging (sterilizing the food and the container prior to filling and sealing) also
follows the same principles.
The food preservation method of canning originated in the early 1800s during
the years of the Napoleonic Wars, the French government offered a hefty cash
award of 12,000 francs to the Inventor, who could devise a cheap and effective
method of preserving large amounts of food. In 1809, Nicolas Appert, a French
confectioner and brewer, observed that food cooked inside a jar did not spoil
unless the seals leaked, and developed a method of sealing food in glass jars
(French, appertaina.com). Appert was awarded the prize in 1810 by Count
Montelivert, a French minister of the interior (Jesse D. Dagoon, 1989). The
reason for lack of spoilage was unknown at the time, since it would be another
50 years before Louis Pasteur demonstrated the role of microbes in food spoilage.
Today canning process is growing in the field of fruits and vegetables. The industry
is made up of establishments primarily engaged in canning fruits, vegetables, fruit

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and vegetable juices; processing ketchup and other tomato sauces; and producing
natural and imitation preserves, jams, and jellies. Canned foods are a significant
component of the diet of most people in both developed and developing countries,
offering a wider choice of nutritious, good quality foods in a convenient form all
year. During canning, both desirable and undesirable changes occur in nutritional
and sensory properties of foods, resulting from heat treatment employed for the
destruction of microorganisms to achieve the desired commercial sterility. The
extent of thermal processing, in terms of both temperature and duration of the
treatment, is dependent upon the chemical and physical composition of the product,
the canning medium and the conditions of storage, determining the product quality
in terms of its sensory properties and nutrient content.
The retail value of the worldwide packaged food category was 1,952 billion
U.S. dollars for the year 2010. That was up from 1,857.8 billion U.S. dollars in
2009 and 1,894.0 billion U.S. dollars in 2008 (Euromonitor International, 2011).
The retail value of the worldwide canned food category, which includes canned
food, canned beans, canned fish/seafood, canned fruit, canned meat and meat
products, canned pasta, canned ready meals, canned soup, canned tomatoes,
canned vegetables, and other canned food, was 173.0 billion U.S. dollars in
2010 compared to 166.6 billion U.S. dollars in 2009 and 167.6 billion U.S. dollars
in 2008. The retail value of the U.S. canned food category accounted for 38.5
billion U.S. dollars in 2010 compared to a retail value of 38.0 billion U.S. dollars
in 2009 and 36.5 billion U.S. dollars in 2008 (Euromonitor International, 2011).
The canning industry accounted for 8.86% of the packaged foods category in
2010 (Euromonitor International, 2011). However, it is still a vital part of the
worldwide food industry and it continues to grow year after year. Thermal
processing, more specifically commercial sterilization, plays an important part
in today’s canning industry because it provides the protocol for producing safe
food that consumers can trust. Due to these treatments, they also accomplish
the objectives of pasteurization, and are capable of rendering the food
commercially sterile. Thus, this particular heat treatment is known as sterilization,
and is the type used in canning. Because of its greater complexity and importance
in the marketing of shelf-stable foods, much of the following discussion will
address thermal processing as applied to the sterilization of canned foods.
Methods of Canning
Method of canning depends on the type of food being canned. Food is divided
into two categories.
High acid foods
Low acid foods

Technology for Canning 137
High acid foods: High acid foods are foods which contain enough acid to
prevent the growth of bacteria, which can’t be killed by boiling. Foods with a
pH 4.6 or less allow the spores to grow. If spores of C. botulinum are allowed
to grow, toxin will form, and consumption of C. botulinum toxin is deadly.
Symptoms from the con-sumption of this toxin develop within six hours to 10
days and include double and blurred vision, drooping eyelids, slurred speech,
difficulty swallowing, and mus-cle weakness. Paralysis of breathing muscles
can cause a person to stop breathing and die unless mechanical ventilation is
provided. Individuals with any of these symptoms should seek immediate medical
assistance (Renee R. Boyer and Julie McKinney, 2013). Exp: Apples, Peaches,
Applesauce, Pears, Apricots, Pickled beets, Berries, Plums, Cherries,
Cranberries, Fruit juices, Sauerkraut, pickles, Rhubarb, Tomatoes and Tomato
juice.
Low acid foods: Low acid foods are foods which contain very little or no acid.
Have a pH of greater than 4.6. This class includes most vegetables, meats,
poultry, seafood, soups, and mixtures of acid and low acid foods such as spaghetti
sauce. These are subjected to spoilage by all the three groups of thermophilic
and mesophilic putrefactive anaerobes, including Clostridium botulinum. The
thermpphilic anaerobe, which may cause flat sours, are of increasing importance
in this group. Exp: Asparagus, Beans, Beets, Carrots, Corn, Hominy, Meat,
Mushrooms, Okra, Peas, Potatoes, Spinach and Seafood.
Types of Canning
Boiling Water Canning: The boiling water bath method used for the processing
of high acid foods. These foods can be safely processed at 212°F (100°C), the
maximum obtainable temperature in a water bath canner at sea level. Boiling
water container made by metal, if it is deep enough for the water to be well
over the tops of jars and there is space for the water to boil freely. The canner
must have a tight-fitting cover and a metal rack with dividers to separate and
hold jars off the bottom of the canner. During the processing rack prevents jars
from bumping together or tipping and permits the water to totally surround each
jar.
The water in the canner should be hot, but not boiling, before loading with jars
of food if the jars have been raw-packed. The water should be boiling if
necessary to adjust the water level. The jars should be covered by 1 to 2 inches
of water for the full processing time so the food in the top of the jar and the jar
closure will be thoroughly heated. The boiling water canner is used for the
canning of fruits, tomatoes, foods with added vinegar and fermented foods.
Jams, butters, marmalades, conserves and preserves are also processed in the
water bath canner.

138 Volume 6: Global Hi-Tech Horticulture
Pressure Canning: For low acid foods and mixtures of acid and low acid
foods are used 240°F to prevent the development of Clostridium botulinum,
the bacteria that causes botulism C. botulinum forms protective, heat-resistant
spores. To destroy the spore, a temperature above the boiling point must be
used, which is created by added pressure if the spores are not destroyed, they
will germinate and produce toxins in the food when it is stored.
For process foods under pressure at a temperature of 240 °F at 15 Psi (116 °C)
steam pressure canner is used. A steam pressure canner is a heavy kettle
designed to operate safely at pressures greater than one atmosphere. The amount
of steam inside the canner must be equipped with an accurate pressure gauge
or weight. To prevent the escape of steam lid must be locked or sealed. The
canner should have a safety valve and steam valve that can be opened or
closed to permit exhausting (venting) air from the canner. It must also be equipped
with a metal rack and dividers to separate and hold the jars off the bottom of
the canner. The rack prevents jars from bumping together or tipping over during
processing and permits the steam to flow uniformly over the jars.
Two types of steam pressure canners are available. One has a dial pressure
gauge, and the other has a weighted gauge to control pressure. Both perform
satisfactorily. The canner operator, however, is cautioned to carefully read the
manufacturer’s directions that accompany the canner being used. The steam
pressure canner is recommended for canning all foods in the low-acid group.
This group includes all vegetables (except tomatoes), protein foods (meat, poultry
and fish), mushrooms, soups and mixed vegetable recipes containing tomatoes.
Procedure of Canning
Preparation: The principal preparation steps are washing and sorting. For the
washing of Fruits or vegetables high-pressure sprays or by strong-flowing
streams of water should be used while being passed along a moving belt or on
agitating or revolving screens. Passing the raw fruits or vegetables through a
series of moving screens with different mesh sizes or over differently spaced
rollers. According to degree of ripeness or perfection of shape fruits or vegetables
are separate into groups by hand and trimming is also done by hand.
Blanching: Treatment of fruits and vegetables with boiling water or steam for
short periods, followed by cooling period to canning, is called ‘blanching’. This
loosens the skin, which process is of particular importance in the case of beet
root and tomatoes. It facilitate close filling in the can and drive out the air from
the tissues. Further it helps to clean the fruits and vegetables and to eliminate
micro-organisms. It also inactivates the enzymes at 82°C temperature, thus
preventing the possibility of discolouration.

Technology for Canning 139
Adding syrup or brine: The cans are filled with hot sugar syrup for fruits and
with hot brine for vegetables. Adding syrup or brine is to improve the taste of
canned products to fill up the interspace between the fruits and vegetables in
the can and to facilitate further processing. The syrup or brine should be added
to the can at a temperature of 79°C to 82°C.
Headspace: Headspace is the space between the food or liquid and the top of
a jar. Pack food and liquid to allow ½ inch headspace unless otherwise specified.
If the jars are too full, some of the contents could bubble out during heat
processing and prevent sealing by sticking to the rim. Too much headspace
may also prevent sealing if the processing time is too short to exhaust all air
from the jar. Run a plastic spatula around the inside of the jar after packing to
remove air bubbles.
Packing the Jar: Plays a large role in heat transfer through the product, this
process can be completed by using one of the following packing processes: raw
or cold pack, hot pack.
Raw or Cold Pack: Places raw food directly in the jar and then hot, boiling
liquid is poured over the contents. The term raw pack is used when referring to
this method when canning meat, poultry or seafood. The term cold pack is used
when referring to this method when canning fruits and vegetables.
Hot Pack: Involves cooking foods in liquid before packing and then the cooking
liquid is poured over the food in the jar. The hot pack method has several
advantages. Heated products are easier to pack into jars because they are
softer. As a result, more can be put into each jar, fewer jars are needed.
However, hot-packed products are not as firm in texture.
Exhausting: In the process of exhausting air is removed from the containers
at the temperature of 79-82°C. The reduced internal pressure (vacuum) helps
to keep the can ends drawn in, reduces strain on the containers during processing,
and minimizes the level of oxygen remaining in the headspace. With this process
extend the shelf life of food products and prevents bulging of the container at
high altitudes.
Closing the Jars: Wipe jar rims and threads with a clean damp cloth to remove
any bits of food that might prevent a seal. Follow manufacturer’s directions for
preheating lids.
Heat sterilization: During processing, microorganisms that can cause spoilage
are destroyed by heat. Different products and size of cans have different
temperature and processing time Acidic products (Apples, Peaches, Applesauce,
Pears, Apricots, Pickled beets, Berries, Plums, Cherries, Cranberries, Fruit juices,
Sauerkraut, pickles, Rhubarb, Tomatoes and Tomato juice) are readily processed

140 Volume 6: Global Hi-Tech Horticulture
at 100°C (212°F). The containers holding these products are processed in
atmospheric steam or hot-water cookers. Low acidic products (Asparagus,
Beans, Beets, Carrots, Corn, Hominy, Meat, Mushrooms, Okra, Peas, Potatoes,
Spinach and Seafood) are processed at 121°C in pressure canner. During
processing two types of sterilizations are used.
a. Boiling water canning
b. Pressure canning
a. Boiling water canning: Fill the canner halfway with clean water. Preheat
water to 140°F for raw-packed foods and 180°F for hot packed foods. Arrange
the jars on the rack. Add very hot water, if needed, to bring the water level up
to 1 to 2 inches above the jar tops, cover the canner tightly. If a pressure canner
is used for boiling water can-ning, leave the cover unfastened and the petcock
open to prevent build up of pressure. Set a timer for recommended processing
time after water comes back to a rolling boil. Keeps water boiling gently and
steadily, boiled for the particular time. Wait 5 minutes before removing the jars.
Fig. 1: Process diagram for fruit canning
VOC and PM Emission
Cooke r
Peele r or
corer
Sort and
grade
Wash
PM Emission
Receiving and
storage
Heat
ster ilizati on Can sealer Steam
exhaustin g
Syrup
mac hin e
Can filler
Chopper and
slicer
Storag e
Labeling and
casing
Water
coo ler

Technology for Canning 141
Fig. 3: Boiling water bath canner
Fig. 2: Process diagram for juice canning
Rack
Boiling water canner
Cov er
1’ to 2’ Water covering jar
1’ to 2’ Airspace for brisk boil
Rack
spac e
1/2”
Juice Canning
PM
Emissions
PM
Emissions
Receiving
and storage Wash Juice
Extractor
Juice
Strainer
VOC
Emissions
Cooler
Flash
Pasteurizer
Peels, Seeds,
and Pulp
Hammermill
Lime
Press
PM
Emissions
Peel
Drier
Dried
Peel
VOC
Emissions
Citrus Molasses Juice
Evaporator
Storage Labeling and
casing
Water
cooler
Can
Sealer
Can
Filler

142 Volume 6: Global Hi-Tech Horticulture
Advantages of Boiling Water Canning: Eeasy for beginners to learn, best
method for fruits, high acid and pickled foods, inexpensive to start.
Disadvantages of Boiling Water Canning: Temperature does not get high
enough to ensure the destruction of microorganisms in food without high sugar
or acid content, longer time period to complete canning process.
b. Pressure canning: Place two to three inches of water simmering or hot in
a canner. Jars are put on a rack of the canner so steam can flow freely around
each one. Watch for steam to escape steadily through the petcock. After 10
minutes of heating, close the petcock or place a weighted gauge on the canner.
This “exhausting” step is very important to remove all the air from the canner.
Air that is trapped in the canner will cause inadequate heating of jars. This step
is needed even for those types of pressure canners labeled “self-exhausting.”
When the correct pressure is reached, set a timer for the recom-mended
processing time. Down the processing time as a double check on the timer
accuracy. If the altitude is above 1000 feet, Pressure of the canner increased
for decreased atmospheric pressure. Watch the canner continuously to be sure
that the pressure stays constant. Fluctuating pressure may cause liquid to be
drawn from the jars and cause some jars not to seal. Check the instruction
manual. When the pressure returns to zero, remove the weight from the vent
port or slowly open the petcock. Wait for 10 minutes than remove the lid carefully
after. Immediately remove the jars. Spoilage could occur if jars are allowed to
stand in the warm canner. Cool jars 12 to 24 hours. Check that the jars are
sealed.
Fig. 4: Process diagram for vegetable canning
VOC and Emissions
PM
Emissions
Cutter Peeler Wash
Can Filler
Receiving
and
storage
Wash Sort and
Grade
Blancher or
Cooker
Steam
exhausting Can sealer
Storage Labeling
and casing
Water
Cooler
Heat
Sterilization

Technology for Canning 143
Fig. 5: Pressure canner
Fig. 6: Step-by-step pressure canning
Jar rack
1-piece safety
counter weight
Weighted gauge
Dia l
guage
Pressure regulator
Vent Port
Safety fuse Gask et Vent

144 Volume 6: Global Hi-Tech Horticulture
Advantages of Pressure Canning: Include: best method for low acid foods,
such as vegetables, foods reach a higher temperature; process is completed in
a short period of time.
Disadvantages of Pressure Canning: Include: startup cost is higher than
boiling water method as a pressure cooker is required can be dangerous if
pressure is not monitored and released some soft fruits can be damaged by high
heat.
Cooling of Jars: Put the jars on a rack or cloth so air can circulate freely
around them. There should not be a cold draft or fan blowing on the jars.
Testing the Seal: Test each jar for a seal within 12 to 24 hours. Jars with flat,
metal lids are sealed if the following:
The lid has popped down in the centre. The lid does not move when pressed
down. The centre of the lid gives a clear, ringing sound when tapped with a
spoon (This is not as reliable as the other methods). If you discover that a jar
has not sealed within 24 hours of the initial processing, refrigerate or freeze the
contents or reprocess. To reprocess, start by removing the lid. Use a new lid
and process again for the full time. The quality of the food will not be as good
after reprocessing. Unsealed jar has found after 24 hours have passed examine
it for spoilage. Do not taste the food. If appearance of food is edible, food
should be boiled for 10 minutes and then refrigerate it. It is not safe to reprocess
at this point.
Storing: Wipe the jars and label them with the date and contents. Rusting is
caused due to the screw band, it should be removed. Store jars in a cool, dark,
dry place. For best eating quality and nutritive value, eat the food within 1 year.
High temperature, low temperature and light decreases the quality and shelf
life of canned food.
Fig. 7: Testing the seal
Press the center with
thumb or finger Note gene ral
“concavene ss” to lid
Listen for high-pitched
ring when lid is tapped
with a spoon

Technology for Canning 145
Canning Safety Precautions: Boiling Water Canning: make sure to use the
proper type of jar and lid. Boil jars for the proper processing time. Do not touch
hot jars with bare hands.
Pressure Canning: check dial gauges know your altitude, as this influences the
pressure required for safe canning handle gaskets carefully and never use those
which are cracked or dried. Do not use jars with cracks or any evidence of
nicks. Do not fill racks to be extraordinarily heavy. Take care around canners
and pressure cookers; they are very hot. Leave the proper amount of headspace.
Do NOT use jars made for commercial canning when home canning.
Commercial Canning
Uses continuous units of pressure canners called retorts. Retorts include:
Continuous Retort
Still Retorts
Agitating Retorts
Continuous Retorts: Allow the cans to be fed through an air lock, then
rotated through a pressurized heating chamber. Pass heated cans into a
second section of the retort which is a cold-water cooler. Continuous
Retorts still and agitating retorts may be batch or continuous. Continuous
retorts have four sections: Can warmer-pressure section-pressure cooler
– atmospheric cooler. These retorts have self sealing valves which maintain
pressure and tolerate temperatures up to 143°C.
Fig. 8: Continuous Retorts
2
3
1
Steam
Water inlet
Water outlet

146 Volume 6: Global Hi-Tech Horticulture
Still Retorts: Liquid food material is often sterilized in still retorts with
steam flowing around the surface of the can, large pressure cookers
capable of handling large numbers of cans. When vigorous agitation is
not working food is sterilized by natural convection. Such situations may
arise during in-package pasteurization of liquids in bottles. Further, agitation
equipment may not be justified when liquid food is processed in low
volumes. Food sterilized in cans include in-packaged heat pasteurized
beer, evaporated milk, thin soups and broth, pureed vegetables, fruit and
vegetable juices and vegetable soups (Datta and Teixeira, 1988; Kumar
et al., 1990). It is important to develop better understanding of the heat
transfer phenomena that are associated with the thermal sterilization
process from the viewpoint of improving its design and operation. This
work focuses on the definition and direct estimation of heat transfer
coefficients obtained during the sterilization process from CFD simulations.
Unified Nusselt number correlations are drawn from CFD simulations on
heat transfer in food cans with different aspect ratios and food medium
thermal conductivities (Karel et al., 1975). Different containers are used:
Plastic containers, flexible pouches, metal trays and glass jars.
Fig. 9: Still Retorts

Technology for Canning 147
Agitating Retorts: Mechanically move the cans, Provide quicker heat
penetration. Some retorts agitate the cans during processing in order to
increase the rate of heat penetration into the cans. Agitation is useful for
products which are too viscous to heat or cool by natural convection. By
using agitation, the process time may be reduced by up to 80%. Mixing is
largely due to the movement of the headspace during agitation and to be
effective there must be a sufficiently large headspace inside the can. A
small headspace may lead to under processing.
Commercial Canning Safety
All processes and facilities are approved by the Food and Drug Administration
Cans are tested for the presence of lead HACCP systems identify all areas of
possible contamination and are in place to prevent contamination from any
source. Commercial canning reaches temperatures and pressure above those
of a home canning operation. Since the processing procedures differ from home
canning, many commercially canned foods have a longer shelf life. Canned
foods are tested by the company and governmental agencies for the presence
of contaminants.
New Technology of Canning
We have used science and technology for thousands of years to help provide
adequate food.
Fig. 10: Agitating Retorts
A-Steam
B-Water
C-Drain,Overflow
D-vents, Bleeders
E-Air
F-Safety Values Pressure Relief
Valves
- Globe
- Gate
A
C
C
F
E
FD
BE
D
B
D

148 Volume 6: Global Hi-Tech Horticulture
The progression from hunter-gatherer to agriculture led to the need to store
and preserve foods. Without some form of processing, foods deteriorate rapidly
due to the action of micro-organisms and enzymes.
Ball brand home canning: There is a new automatic canning system on the
market in which you still have to prepare the recipe for canning and clean the
jars, lids, and bands beforehand but it will preheat your jars and process your
food for you. It also removes some of the responsibility, an array of sensors.
That means you won’t have to stare at water boiling for a prolonged period of
time and you won’t need to worry about things like altitude, or the time and
temperature required to safely preserving the foods. This new appliance is not
a pressure canner. It works with recipes that fit the category of boiling water
canning only, and only with specific recipes provided by the manufacturer. The
boiling water approach is only safe with acidic foods like jams and jellies, fruits,
tomatoes, salsas, pickles, and fruit sauces. Low acid foods like meat and
vegetables have to be preserved in a pressure canner to rule out potential botulism
contamination.
They must be used as stated to ensure the proper acidity for the canning process.
The capacity of this canner is three quart jars, four pint jars, or six regular
mouth half pints. Stacking jars inside the canner is not recommended, so if you
were to use wide mouth half pints, it would only be able to hold four. It may also
be desirable for people who want to can but have small kids or work
responsibilities that makes it hard to tend a canning pot. Once the food is prepared
and jars filled, you put the jars in the appliance, select the proper setting, and let
the pre set cycle for processing take place. You just have to stay close enough
to open it and remove the jars once the time is up (www.FreshPreserving.com).
Fig. 11: Ball brand home canning

Technology for Canning 149
Jarden Home Brands, makers of Ball brand home canning products, today
announced the first of its kind appliance revolutionizing the fresh preserving
process, the Ball Fresh TECH Automatic Home Canning System. This unique
counter top appliance takes the guesswork out of the home canning process
and enables consumers to auto preserve freshly made foods with the push of a
button, using up to 30% less time, 60% less energy and 85% less water when
compared to traditional water bath canning methods.
New wine canning technology to customers: Amcor has developed an
innovative solution for filling cans with wine. The patented Rose worth process
allows winemakers to can wine without using special wine making techniques.
Wine in cans gives consumers a safer and more convenient choice for situations
such as sporting events, night clubs and picnics. The Rose worth process creates
growth opportunities for winemakers in Australia and New Zealand by helping
them develop new markets and market segments. Convenient and portable
packs can be configured to many secondary packaging options, creating new
choices for consumers. Jonathon Lock head, National Sales and Marketing
Manager for Amcor Beverage Cans, sees considerable potential for this
innovative technology. “Putting wine into cans is a great concept that can help
expand our customers’ businesses by allowing them to supply products that tap
into the ‘convenience’ and ‘on the go’ consumer trends. The use of premium
slimline and shaped cans helps winemakers further differentiate their products
in what can be a crowded marketplace,” Lock head said. Canned wine has
excellent shelf stability, is easily chilled, and offers a sturdy packaging format.
The light weight and recyclability of aluminium cans also underpin the strong
environmental credentials of the canned wine option. Amcor was able to create
the leading edge process through its understanding of the technical issues of
canning wine.
The new technology is supported by Amcor’s global research and technology
development capability and international network of partners. A range of can
sizes and shapes, including custom shaped cans, are available. Amcor can also
support its customers with design capabilities and complementary packaging.
Miami Beach: A major innovation in food processing that eliminates undesired
mushiness in canned vegetables and fruits have been announced by a scientist
from Cornell University.
The new process produces canned carrots, beans and other vegetables almost
as firm and crunchy as fresh produce. It also works to a lesser degree on fruits.
Dr. Malcolm C. Bourne, developer of the process, described it as one of the
most exciting advances in canning technology since Nicholas Appert delighted.
Bourne predicted it will have a farreaching impact on consumers and food

150 Volume 6: Global Hi-Tech Horticulture
processors within two to five years. We think the time will come when half the
items in the salad bar or the stirfry pan in your favorite restaurant will come
from tin cans instead of the refrigerator, said Bourne, an authority on food
texture and a professor of food science and technology at Cornell‘s agricultural
research centre. Likewise, the process could help to reverse a long decline for
the canned fruit and vegetable industry, whose sales have been falling about 1
percent a year for 15 years.
Bourne said that consumers demanding vegetables with a firm, crisp texture
have forsaken canned produce for frozen or fresh vegetables. He reported
development of the new process at the 198th national meeting of the American
Chemical Society. It originated through basic understanding of the chemical
changes that occur in fruits and vegetables during cooking. Cooking softens the
texture of fruits and vegetables by unravelling the molecular structure of pectins.
The longer the heating time, the softer the fruit or vegetable becomes. The
problem is especially serious with canned vegetables, which must be heated for
long periods to kill bacteria that cause spoilage. The new process involves
reducing blanching temperatures and adding a brief holding period to allow a
naturally occurring enzyme to “fix“ the crispness in fruits and vegetables. The
enzyme, pectin methyl esterase, reverses some of the softening effects of
cooking. The process also involves the addition of calcium, which the enzyme
uses to repair cooking related damage in pectin, and citric acid to produce the
required acidic conditions. Bourne said three commercial canning firms already
are evaluating the process, which has been patented by Cornell.
Conclusion
Canning is an important and safe method of preservation if practiced properly.
The canning process involves placing food in jars and heating the jars to a
temperature to destroy microorganism that could be a health hazard or cause
the food to spoil. There are different methods of canning for fruits and vegetables.
This heating also destroys enzymes that may cause undesirable changes in the
flavour, colour and texture of vegetable. Air is driven from the jar during heating
and it is cool, a vacuum seal is formed. The vacuum seal prevents air from
gating back in to the products, bringing with it microorganism that would
decontaminates the food.
References
Jesse D. Dagoon, (1989). Applied Nutrition and Food Technology, p. 2.
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Datta, A.K., Teixeira, A.A., (1988). Numerically predicted transient temperature and velocity
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Technology for Canning 151
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