Canning is a method of food preservation where food is packed in airtight containers and heated to destroy microorganisms. The document outlines the steps in canning including preprocessing, filling containers, removing air, sealing, heat processing, and cooling. Some key advantages of canning are that the products have a long shelf life, are ready to eat, and can be stored at room temperature. The history of canning is discussed, noting Nicholas Appert's pioneering work in the late 18th century. Improvements to thermal processing over time are also summarized.

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Canning as a method of preservation
1.1.Introduction to Canning
It has been a great struggle for man from the beginning not only to collect and produce
food but also to preserve the produced food. Hence, several food preservation methods
such as sun drying, salt curing and drying, smoking, chilling using ice etc. were
developed from the very early days of civilization. The practice of keeping the food in
metal/glass containers and heat processing came into existence in the late 18th
century. This process of preservation is referred as canning, which is the verb form of
the word ‘can’ which means a metal container.
1.2.Definition of canning
Canning is a method of food preservation in which food is packed in metal or glass or plastic
containers, sealed air tight and heated sufficiently to destroy the spoilage, pathogenic and food
poisoning organisms making the food safe for consumption.
1.3.Steps involved in canning
The steps involved in the canning process are as follows.
Pre-processing operations: Depending on the nature of the food, different preprocessing
operations are carried out. Washing, separation of edible parts, cleaning, cutting into desired
size and shape, brining, precooking, blanching, frying etc are done prior to filling of the can. The
difference in canning method for various foods stuffs lies in this stage.
Can filling:The preprocessed food is filled in to the cans along with suitable filling medium. The
quantity of food to be filled varies with the size of the can. Sufficient space has to be provided
between the lid and the top layer of the food.
Exhausting: The exhausting is the process to remove the air and gases inside the filled cans.
This is achieved either by using steamor by creation of vacuum by a pump. The removal of air
prior to can closing creates vacuum in the head space.
Can closing/seaming: Can closing or seaming is a process wherein, the lid and the body of the
can are tightly sealed. This is done by can seamer. Can closing should be airtight preventing the
exchange of gases between atmosphere and inside of the can.
Heat processing (Retorting): Retorting is a process where the closed cans are subjected to heat
processing at high temperature to destroy spoilage and pathogenic microorganisms. This is the
most important step in canning. The temperature and duration of heat processing depend on
the type of food, size and shape of can
Cooling of the cans: After heat processing, cans are cooled immediately either in air or more
commonly in water to the ambient temperature. Cooled cans are dried, labeled and stored.
1.4.Advantages of canning

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 Canned products are safe and will not cause any ill health (or allergy etc)
 Canned product are ready to serve products and hence instantly available for
consumption with little or no further preparation for the table.
 Canned product can be made available at any place any time.
 Canned products do not require special storage facility such as cold storage. Ordinary
room temperature storage is sufficient.
 As inedible portions of foods stuffs are removed, it represents concentrated form of food
 Canned food has long shelf life measured in years not in weeks or months. The shelf life
is about 2 years.
 Wide range of food products can be preserved.
Unit 2 - Historical developments in canning technology
2.1.Historical developments in canning technology
It is well known that man learnt the art of food preservation even in the prehistoric days.
However, the principle of food enclosed in a can/bottle and subjecting it to heat so that the food
could be preserved for a long time was developed by Nicholas Appert, a French confectioner.
In the early 17th century, the scientific community was involved in establishing whether life
develops from the living things or from lifeless materials. John Needham in 1745 put heated food
in clean bottles and the food spoiled in few days due to microorganisms and he gave the theory
of spontaneous generation of life. However, later it was realized that he had forgotten to use
cleaned sanitised lids or closures which led to microbial contamination.
Napoleon, the then ruler of France, had ambition to conquer greater part of the world. The
French army moved not only throughout Europe but also to Africa, Asia and East Indies Islands.
As French sailors of the navy had to remain in sea for a long time and during this period they
depended on dried foods, salted foods. Several of them died because of diseases including
nutritional deficiency like scurvy. This made Napoleon to announce a prize of 12,000 Franks to
anyone who preserves food for a long time without any loss of nutrients. Food was the main
business of Nicholas Appert, and this announcement attracted him to prepare various foods in
proper manner. He filled them in glass containers and closed air tight using closures and
subjected to heat treatment. He worked from 1795 to 1804 and preserved more than 50 food
products. The products were given to French Navy officers to verify whether the products
remained good not only in temperate climate but also in the tropics, where the temperature is
high.
Appert’s work not only got several accolades for him, but also responsible for the development
of several food preservation industries in various countries. The method of preservation
described by Appert is more or less the same as followed even today and thus referred to as

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Appertization.
The present day canning technology has evolved from inputs from different fields like food
microbiology, can making technology and the science of heat processing.
2.3.Progress in thermal processing
In Appert’s process, the maximum temperature reached was 1000C. Hence, for some
foods, a long time heat process extending upto 3 to 4 hours was required to prevent
spoilage. In order to reduce the heat processing time, temperature more than 1000C
was required. Fostier in 1839 used common salt or other salt solutions to elevate the
boiling point and hence the temperature of processing. However, use of salts caused
corrosion of vessels. In 1843, Winslow and Reymond Chaneliar Appert used steam
under pressure to get elevated temperatures and reducing the processing time. In 1874,
Scheiner, produced steam separately and used for heat processing of cans. At present,
the same process is being used in industry for heat processing of canned foods.
In the beginning of 20th century, research was conducted to assess the heat resistance
of microorganisms, heat penetration into the cans and thermal process calculation. In
this field the contribution of Bigelow, Ball, Olson, Stevens and Stumbo are noteworthy.
Using the principles of thermal processing, High Temperature Short Time (HTST)
process and aseptic packaging have been developed.
2.4.Developments in fish canning industry
Year Development
1817 William Underwood packed lobster in glass containers in Boston.
1824 Salmon canning started at Aberdeen, Scotland.
1843 Mackerel canning
1844 Oyster canning
1864 Fish canning industries started on the West coast of the USA, Canada, Alaska, Russia and
Japan.
1867 Dunbars first canned shrimps in Gulf of Mexico.
1870 Canning of sardine became popular in Spain, Portugal and Morocco.
1917 Canning of tuna started in California.
1959 Export of canned shrimps from India.
1970’s Several shrimp canning industries came up in India.
3.1.1.Raw materials and other ingredients for canning
The purpose of canning is for long term preservation of food stuffs and hence raw
material is an important requirement of the industry. The prime quality of raw material
should be available for canning. The raw material used in canning can be classified as
follows.
Agricultural produce - Fruits e.g.: Apple, orange, pineapple, pears, peaches, berries,

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cherry, mango, guava, papaya and jackfruit. Vegetables - Green Beans, carrot, peas,
corn, spinach, cabbage, potato, beetroot, bamboo shoots etc.
Animal produce - Land animal e.g. Pork, Beef, poultry meat, mutton. Aquatic animal –
e.g. crustaceans, marine mammals including whales, fishes such as salmon, tuna,
mackerel, sardine, herring, pilchard, pikes, seer, pomfret etc and shellfishes such as
crabs, lobsters, shrimps, cuttlefish, clams and green mussels.
Others - processed foods such as condensed milk, soups, baby food and milk powder.
3.1.2.Desirable characteristics of marine products for canning
 The fish should be in fresh condition and should have not reached autolysis
stage.
 Fish with high dressing yield is preferred for canning.
 The fish meat should be firm enough to withstand the normal heat processing
during canning. The fish meat should not disintegrate after canning.
 The colour of the meat should be light or white. Fish meat with dark pigments will
discolor the final product.

3.1.3.Portions of fish used for canning
Generally small pelagic fishes like mackerel, sardine and anchovies are canned
with skin and bones; hence the skin should have lustrous shining appearance.
Meat chunks of large fishes like tuna, seer fish and catfish are canned.
Only the edible portions of shrimps, clams, oysters, mussels and crabs are used
for canning.
3.1.4.Ingredients for canning
Other than raw material, the important ingredients used in canning of fish are,
 Salt
 Oil
 Additives like spices (other ingredients)
The quality of ingredients used for canning of fish will have effect on the final quality of
the product.
3.1.4.1.Salt
Salt is used in the preparation of brine and the concentration of salt used may vary from 6-8% to
saturated salt solution. Brine is used for dip treatment to dressed fish prior to canning, blanching
of peeled and deveined prawns (6 to 8% boiling brine) and as filling medium (1-3%) salt in fish
cans. The brining improves the texture of the fish.
The impurities in salt such as chlorides and sulphates of magnesium will lead to bitter taste of the
product. If the above mentioned magnesium salts are present in more than 0.1% in canned fish, it
results in the formation of ‘struvite crystals’. Struvite crystals are glass like structures and are
undesirable in canned products.
Quality of salt used for canning

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 The salt used in canning should be pure and should not contain more of soluble and
insoluble impurities. The soluble impurities should not be more than 1.5% and insoluble
impurities should not be more than 0.5% when it is used for can filling.
 The counts of halophilic bacteria and pathogenic bacterial spores in salts should be low.
 The salt should have minimum of 98% sodium chloride content, should be of small
crystal size for easy dissolution. Some table salts are added with Magnesium carbonate
and Calcium carbonate to maintain free flow characteristics and hence such salts have to
be avoided.
3.1.4.2.Vegetable oils
For canning different types of fish, vegetable oil is used as filling medium. Vegetable oil is also
used in preparation of filling medium for canning. Refined cottonseed oil, groundnut oil,
sunflower oil and soybean oil are primarily used.
Quality of oil used for canning,
 Free from moisture content is suitable.
 Specific gravity should be between 0.9-0.92.
 The oil should have less of unsaturated (iodine value should be less) fatty acids.
3.1.4.3.Other ingredients
In order to enhance taste and flavour of canned products spices such as chilli, pepper,
cardamom, cumin, ginger etc are used. These are available in dried form and contain high load
of bacteria and spores. Bacterial load can be reduced by cleaning and roasting or by sanitisation
using fumigants or by irradiation. Alternately, oleoresins and essential oils of spices are used to
avoid microbial contamination.
3.2.1.1.Preparation of raw material for canning
Preparation of raw materials for canning includes steps such as cleaning, washing,
sorting, dressing, trimming, size cutting, mixing, mincing, brining, blanching, precooking,
shucking, frying, smoking and grading.
If the frozen fish is used for canning, thawing is an important step. Thawing is a process
of converting solid ice to water in a frozen fish. Thawing is done either in air or in
running water till all ice of the fish melts.
If the fresh fish is used for canning it should be chilled immediately. It is important to
keep the fish in chilled condition during all pre-processing operations.
3.2.1.2.Washing
Washing of fish has to be done using adequate quantity of chilled water (either by using
ice or by refrigeration). Immediately after washing, the fish should be iced in order to
avoid microbial and enzymatic spoilage.
3.2.1.3.Dressing
Dressing is a process of removing head viscera, gills and fins and the rest including skin
and bones (considered as edible) go into cans. Sometimes, heads and small fins are

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not removed. Some fishes have to be washed, dressed and cut to required size
depending on can dimension.
3.2.1.4.Brining
Brining is an operation where the dressed fish is dipped in saturated brine solution for 8-
15 minutes depending on the thickness of dressed fish, brine temperature and nature of
fish. Brining removes blood, dirt, slime and other undesirable materials attached to fish.
Further brining helps in improving the texture of meat by removing moisture.
3.2.1.5.Precooking
Precooking is done to remove excess moisture and fat from the fish. This can be achieved by
steaming, frying and blanching. By this method the fish becomes firm and also the moisture
content comes down. After precooking, fish meat looks bright and more attractive. However,
there will be some loss of taste and flavour components.
Precooking by steaming is done in retort for 30-45 minutes which expels moisture and fat and
can be removed by draining.
Frying is done using refined vegetable oil at a temperature of 160 to 180oC for one to three
minutes. Frying results in reduction in moisture, firming of texture, reduction in size and
improvement in taste and flavour.
Blanching is one of the precooking methods where the fish/shrimp is dipped in boiling brine
containing 6-8% salt for 4-6 minutes. Use of citric acid in blanching of shrimp is a normal
practice to achieve better colouration and texture. Blanching results in contraction and curling
of shrimp, reduced moisture content, development of firm texture and attractive colouring.
Blanching of shrimp helps in controlling the net weight of shrimp in the processed cans.
Live clams, green mussel, oysters and crab are washed, steamcooked for a few minutes to
open the shell and to collect the edible portion. It is essential to remove blood from crab meat
which otherwise results in blue discolouration.
In tuna, the precooking operation helps in easy separation of dark and light meat. The dark
meat is not packed in can as they are not appealing and normally goes for pet food
preparations.