STERILIZATION/ CANNING PROCESS
Canning/Sterilization
Canning is a method of preserving of food which consists of heating the food and
sealing it in an air tight containers. The advantage of canning is that the food can be keep a
long period of time and is always ready for use.
Sterilization means no viable microorganism is present. Commercial sterility
indicates that no spoilage occurs under normal conditions of storage and handling.
Kinds of Canning
a. Water bath processing / open kettle processing: process temp of 100°C; used
for medium acid (pH between 3.7 – 4.5) and high acid (pH below 3.7) foods.
Fig. 18. Water bath processing
b. Pressure processing / retorting: process temp above 100C using pressure
cookers or retorts; used for low-acid foods (pH above 4.5). Low acid foods
should be processed at 121°C (15 psi) for 15 minutes
Fig. 19. Pressure processing
Canning Equipment:
1. Water bath.
2. Pressure canner. Pressure canners are available in different designs, materials and
sizes. Directions for use should accompany each canner. Follow these directions
carefully.
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3. Exhausting steamer
Containers for Canning
1. water bath processing – glass jars, bottles
2. pressure processing – metal cans (tin cans or aluminum cans), pouches
Packing Liquids
1.
2.
3.
4.
5.
Water
Syrup for fruits
Brine for vegetables
Oil, sauce for fish and meat
Fruit juice or fruit pulp or blend of fruit juices or fruit pulps, unsweetened or
sweetened.
To make syrup:
a. light syrup : 400g (2 cups) sugar to 1 liter (4cups) water
b. medium syrup: 600g (3 cups) sugar to 1 liter (4cups) water
c. heavy syrup: 850g (4 1/4cups) sugar to 1 liter (4cups) water
Depending on the concentration in Brix degrees (°Brix) measured in the
final product, shall be designated as follows:
a. Extra light syrup or slightly sweetened syrup greater than or equal
to 10° but less than 14°Brix
b. Lightly sweetened: greater than or equal to 14° but less than 18°
Brix
c. Heavily sweetened: greater than or equal to 18° but less than
22°Brix
d. Extra heavy syrup: greater than or equal to 22°
When using fruit juice, the fruit content exceeds 50%, with the exception
of strong flavored and/or highly viscous juices (e.g., mango, guava,
cranberry, passion fruit, etc), in which case the fruit content could be less
than 50%.
The product may also be designated as:
a. “solid pack” - meaning whole fruit or pieces of fruit, without any
added liquid or with only a small amount of liquid, and with or
without foodstuff with sweetening properties such as sugars or
honey
b. “regular pack” - meaning whole fruit or pieces of fruit with liquid
packing medium.
The Canning Operations:
1. Raw materials handling – observe hygienic practices particularly the
implementation of Good Manufacturing Practices (GMP) and Hazard Analysis
Critical Control Points (HACCP); adopt the GIGO (Garbage in-garbage out)
paradigm.
2
2. Pre-treatments – includes washing, gutting, nobbing, filleting, shucking, shelling,
peeling/paring.
3. Pre-cooking – for some products (esp. tuna or other fishes), specific dishes like
lechon paksiw, pork dinuguan, laing,etc.
Reasons for pre-cooking:
to partially dehydrate the flesh and prevent release of those fluids
during retorting
to remove natural oils, some of which have strong flavor
to coagulate fish protein and loosen meat from the frame
to develop desirable textural and flavor properties
to make the flesh firm and in the case of the crustaceans aid in their
release from the shell
4. Filling
- methods of filling:
a. Hot Filling / Hot-pack method: standard temp of 85°C (185°F)
Heating the food to a target temperature then filling into bottles while still
hot.
Foods that are hot-filled:
a. Highly acidic products (pH 3.7 or below) or those which contain
a lot of vinegar like ketchup and pickles.
b. High salt sauces (25% salt)
c. High sugar products (69% soluble solids) like jam, jelly and
preserves
b. Cold filling / Cold pack / Raw packing method: food is heated in container prior
to sealing.
Fill jars with raw food and cover with boiling hot syrup, juice or water.
Pack raw fruits and vegetables tightly, because they tend to shrink during
processing.
Pack raw corn, lima beans and peas loosely, because they expand.
Headspace
The headspace is the area inside a container that is void of product. Adequate
headspace must be provided when filling to allow for expansion caused by heating the
product. If no headspace is allowed for expansion, the pressure build up can damage the
hermetic seal or can cause the lid to flip during processing.
a. Net headspace – the space between the inside surface of the lid and the
surface of the product; done for homogeneous liquid products.
b. Gross headspace – it is the vertical distance between the level of the product
and the top edge of the container; done for non-homogeneous liquid products.
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 Peaking or buckling: deformation of the can end caused by extreme internal
pressure build up during heating process. Overpressure if over 15psi (121C)
5. Exhausting - removal of air from the food in the container; it will ensure a vacuum in the
canned food. The desired vacuum for canned/ bottled foods is 1020 inches of mercury.
Vacuum is necessary for the following reasons:
a. prevention of distortion during thermal processing
b. maintenance of can ends or bottle caps in concave position during normal
storage
c. reduction of oxygen which can react or discolor the product
Vacuum is usually measured by with a Bourdon-type gauge calibrated to read
vacuum from 0 to 30 inches.
A low oxygen in canned foods is desirable to minimize adverse chemical changes in
the product such as oxidation of fats or vitamins, to prevent discoloration in some
products and also to reduce internal corrosion of the cans.
For exhausting, use exhaust box, a steamer or a water bath.
During exhausting, the cans/bottles are left open without the lid on, to allow
maximum escape of internal gases.
6. Sealing of container
A successful seal is an essential factor in canning. A seal defect or failure will
make the product unsafe or not shelf-stable. Use can sealers for cans and
automatic sealer for bottles.
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7. Retorting (Pressure processing) – subjecting to pressured steam in a retort or
pressure canner. The sterilization process in the canned product can be subdivided into
three phases:
a. By means of a heating medium (water or steam) the product temperature is
increased from ambient to the required sterilization temperature (phase 1 = heating
phase).
b. This temperature is maintained for a defined time (phase 2 = holding phasing).
c. In (phase 3 = cooling phase) the temperature in the can is decreased by
introduction of cold water into the autoclave.
Retorts – it is a batch-type, non-agitating, vertical or horizontal pressure vessel
used for processing foods packaged in hermetically sealed containers.
Generally, containers are stacked or jumble-loaded into racks, crates,
baskets or trays for loading & unloading the retort.
In a steam retort, the pressure at 250F (121C) is 15 psi (pound per
square inch). Any pressure supplied to the retort in excess of the 15 psi
is referred to as overpressure.
Vertical autoclaves / retorts. Simple small autoclaves are usually vertical autoclaves
with the lid on top. Through the opened lid the goods to be sterilized are loaded into the
autoclave. The cans are normally placed in metal baskets. The baskets are placed in the
autoclave, either singly or several stapled on top of each other. Before starting the
sterilization, the lid must be firmly locked onto the body of the autoclave. The autoclave and
lid are designed to withstand pressures up to 5.0 bar. These types of autoclaves are best
suited for smaller operations as they do not require complicated supply lines and should be
available at affordable prices.
Fig. 20. Vertical Retort
Horizontal autoclaves / retorts. Larger autoclaves are usually horizontal and loaded
through a front lid. Horizontal autoclaves can be built as single or double vessel system.
The double vessel systems have the advantage that the water is heated up in the upper
vessel to the sterilization temperature and released into the lower (processing) vessel,
when it is loaded and hermetically closed. Using the two–vessel system, the heat treatment
can begin immediately without lengthy heating up of the processing.
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Fig. 21. Horizontal Retort
8. Cooling: Cans should be rapidly cooled to 40°C to prevent germination of thermophiles
which cause spoilage. Cooling of the canned foods also is influenced by the
same factors as the heating process. Rapid, artificial cooling is usually
adopted to effect a greater control on the cooling rate, because slow cooling
may cause overcooking of the food and also allow the growth of thermophilic
organisms.
9. Storing: Temperature in storage rooms should be kept cool within 20-30°C. Very humid
conditions, external rusting may occur.
HEAT PENETRATION IN CANNED FOODS
Heat penetration
-
is designed to measure the rate of heating of the food product under consideration
-
thermocouples or other temperature measuring devices are inserted into the
containers to measure the product heating rate.
-
not only should the slowest heating container in the test be identified, but also
the slowest heating zone within any given container.
-
the performance of heat penetration work must be based upon adequate knowledge
of the heat resistance of the microorganism(s) of concern in the specific product to
be processed.
-
The information developed during the heat penetration test is then used to calculate
a theoretical process.
-
The theoretical process may be confirmed by using an inoculated pack. In an
inoculated pack a known amount of an organism with a known heat resistance is
placed into each container. The containers are then processed at various calculated
process times and/or temperature(s) and examined for surviving organisms. The
objective of the inoculated pack method is to determine the time/temperature
combination that will kill all of the spores added to the product.
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Factors Affecting Time of Thermal Process
The thermal process time necessary for preservation of a chosen food depends on
the rate of heat penetrating into a food. Since every part of the food in a container or can
must receive the same adequate heat treatment to prevent its spoilage, the process time
work depended on the part which receives heat most slowly.
The food part near the center of the container usually receives heat most slowly. Heat
penetration in food is mainly due to conduction as well as convection, which may operate
simultaneously or successively. Conduction occurs in solid particles of foods and is slow
while heat transfer by convection occurs in liquids.
1. The material of the container – glass having a slower rate compared to that of a
metal.
2. The size and shape of the container – smaller and slim cylindrical cans attain the
desired temperature faster.
3. Initial temperature of the food - a higher initial temperature provides the lethal range
for the microorganisms for a longer time and its average temperature during heating
is higher than the food in the can with a lower initial temperature. A higher
temperature is necessary for foods which heat slowly, e.g. meat, pumpkin etc.
4. Retort temperature a higher retort temperature heats the food rapidly.
5. Consistency of the food – nature, sizes and shapes pieces decide the rate of heat
penetration.
For example, tomato sauce on baked beans slows down heat
penetration more compared to plain sauce.
Starch concentrations up to 6% decreases heat penetration, but at
higher concentration, has no additional effect.
Sodium chloride does not influence heat penetration, as its concentration
is usually low.
Increasing of sugar decreases heat penetration.
6. Rotation and agitation of the container during heat processing hasten heat
penetration, particularly if the food is a fluid, but may cause undesirable physical
damage to some solid foods.
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How to estimate heat penetration
Use the growth-no-growth method
Use a series of test tubes or vials at each time interval. Obtain data and plot
Thermal Death Time (DTD) curves on logarithmic paper where temperature is
plotted as arithmetic values and time in minutes as logarithms or on a logarithmic
sacle (see Table below).
As a safety measure, the canning industry has recommended a 12D heat treatment
(enough heat or process lethality to reduce 1012 spores per millileter)
Table 15. Thermal Death Time Data
Temperature
110C
115C
121C
Corrected heating time
(min)
25
40
60
80
110
140
10
14
18
22
28
36
3
4
5
7
10
13
Number of Samples
Heated
Positive
6
6
6
6
6
6
6
5
6
0
6
0
6
6
6
6
6
6
6
2
6
0
6
0
6
6
6
6
6
2
6
0
6
0
6
0
8