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are a stronger marketing appeal, metal savings of

around 15%, depending on the can diameter, and a

significant cutback of end sealing compound. Tests

have shown no significant differences in the perform-

ance between cans closed by the conventional double-

seam and those closed by the Microseam. More

recently, Alcan has also developed smaller seam

designs, using specifications similar to those de-

veloped for Microseam, but for beverage aluminum

can ends: Mini and Reduced seams.

0010 The Econoseam is another novel seam design de-

veloped by Krupp (Figure 8). This is a method of

seaming in which the folds are made in the horizontal

rather than in the vertical plane. The material con-

sumption for can ends to be fixed through Econoseam

is around 28% lower for 73-mm-diameter cans, as

compared with conventional seams. Besides metal

savings, the elimination of the base rim may be an

advantage in preventing transit damage resulting

from rim-riding impact. However, this design did not

achieve widespread acceptance in commercial terms,

because of competition with two-piece cans.

Shaped Cans

0011 Recently, new styles of cans appeared in the market.

Odd-shaped cans were developed because of

marketing factors, as their novelty leads to product

differentiation. However, other issues such as mater-

ial saving and performance improvements are also

behind innovations regarding shaping cans.

0012 As mentioned previously, beading provides extra

strength to the can wall. Although circumferential

beads are commonly used, other beading designs

have been developed. The honeycomb beading

(Figure 9) is claimed to offer at least 15% material

savings, because it supports thinner gauge steel at all

levels of performance. These cans are marketed as

Hexacan and are commercially available in diameters

of 73, 83, 99, 127 and 153 mm.

0013Another enhanced can design is the fluted can. The

food steel three-piece can developed by CMB Food-

can in the early 1990s and designated as the Quantum

can is an example of a fluted can. It has vertical

body flutes that act as a support to provide a

strong, high-quality, thin-walled can, with enough

elasticity to withstand the expansion and contraction

stress experienced during the product thermal treat-

ment (Figure 10a). More recently, Anheuser-Busch

developed a similar design for aluminum beer

cans. This development was marketing-driven, since

the fluted can assists in product differentiation

(Figure 10b).

0014Shaped aluminum draw-wall-ironed cans often

require thicker starting metal gauges, as in the case

of the 500-ml beer-glass-shaped can of Heineken beer.

The can is manufactured by CMB UK, using the high-

pressure gas expansion technique. The can is pro-

duced in a conventional manufacturing line and

then expanded in the radial direction at the top and

bottom to form a shape common to glasses used for

drinking beer. The shape, together with the printed

decoration showing a typical gold yellow beer color

with white foam on the top, yields an attractive and

different image (Figure 11).

fig0008 Figure 8 Novel seam design – Econoseam.

fig0009Figure 9 Hexacan with honeycomb beading. From The Can-

Ltd. Reprinted with permission.

836 CANNING/Recent Developments in Can Design

0015 Another marketing-driven innovation on can

design is the Coca-Cola contour can, a bottle-shaped

two-piece aluminum can (shown in Figure 1). The

can’s external dimensions are similar to the industry

standards, thus requiring no significant changes in

filling lines. The can is higher to compensate for the

loss in volume resulting from the ribbed body. The can

requires 15% more aluminum to impart the strength

required during the filling and seaming operations.

0016Sollac has recently launched a new shaped steel

can-making process – the full body necking process.

Unlike other can-shaping systems, this process uses

standard gauge steel and centers on a necking process

that first reduces the diameter of a standard can,

which is then expanded into the desired form

(Figure 12). The finished can shape is formed by

high-pressure water jets forcing the reduced can

diameter out into a shaped mold. The major advan-

tages of this process are claimed to be the possibility

of fitting into the existing draw-wall-ironing produc-

tion lines whilst maintaining identical productivity,

no increase in the quantity of steel, and costs similar

to those of straight-walled aluminum cans.

0017Can performance may also be optimized by using a

design that allows for a greater amount of product to

be packed. The Caronde can from Carnaud Metalbox

(Figure 13) is one such example. This can is manufac-

tured from a cylindrical can body wall, which is

shaped into a squared body, affording around 18%

more volume of product.

0018The stackability of three-piece cans is a feature

introduced only recently and is becoming increasingly

important, because of the risk of products tipping

over in retailers’ displays. The design of the base

of most two-piece cans and the typical neck-in in

fig0011 Figure 11 Beer-glass-shaped can. From The CanMaker June

with permission.

fig0012Figure 12 New shaped steel can-making process from Sollac.

Publishing Group Ltd. Reprinted with permission.

fig0010 Figure 10 Two examples of fluted cans. From The CanMaker

lishing Group Ltd. Reprinted with permission.

CANNING/Recent Developments in Can Design 837

two-piece drink cans allows these cans to be stacked.

This does not apply to regular three-piece cans, in

which the dimensions of the top and bottom of the

can are the same, and so the bottom of the upper can

does not fit in the top of the underlying can. The

formation of a neck-in in just one end of the can

reduces the diameter and allows that end to fit in

the opposite end of the next can, thus forming a stable

pile (Figure 14). Furthermore, the use of one end

smaller in diameter contributes to a reduced can

weight and hence reduced costs. Stackability and

weight reduction are the major drivers for the in-

creased use of neck-in in three-piece cans.

Polymer-coated Metal Cans

0019 Changes in can coatings have been influenced by

environmental legislation, food-contact legislation,

and trends in can making. Laminates and extruded

coatings are currently under development, some of

them having already been introduced on to the

market. These new types of can coatings imply new

can-manufacturing technologies and are related to

can design and decoration.

0020 In laminates, the metal sheet is coated by lamin-

ation with prefabricated thermoplastic polymeric

films. The metal substrate, whether tinplate, tin-free

steel, or aluminum, is coated on both surfaces with

one layer of polyethylene terephthalate (PET) or poly-

propylene (PP). The advantages of laminates over

traditional wet coatings include the good properties

for food contact and the negligible emission of vola-

tile materials. Also, laminates confer an excellent

appearance and abrasion resistance to the external

layer, combined with very good barrier properties

between the food product and the metal of the in-

ternal layer. Cost is the major drawback, and some

laminates require the use of a tie adhesion layer

(epoxy, phenoxy, or phenolic) between the PET and

the metal substrate, which may raise problems

regarding the suitability of the can for food contact.

0021Ferrolite is a laminate produced by Corus Pack-

aging Plus under license from Carnauld Metalbox.

The metal substrate (tinplate or tin-free steel) is

heated before application of PET to the external sur-

face of the steel and PP to the internal surface. PET

film imparts a high resistance to abrasion and a glossy

appearance, whereas PP provides a protective barrier

between contents and metal. The system allows for

different types of film, colors, and thickness to be

applied to each opposite surface. The resultant com-

posite sheet passes through a second induction heater,

which melts the polymeric films. After holding for

a few seconds at high temperature (260



C), the

fig0013 Figure 13 Caronde can from CMB Packaging (France). Re-

printed with permission.

fig0014Figure 14 Stackable three-piece can from Ferembal (France).

Reprinted with permission.

838 CANNING/Recent Developments in Can Design

composite sheet is cooled down by quenching in

controlled conditions in a water bath (Figure 15).

0022 The other major laminate, Andrafol, is produced

by Toyo Kohan (Japan). This is a tin-free steel lamin-

ated with PET and/or PP. The polymeric film may also

be combined with lacquer on the opposite metal sur-

face. The production system has three alternative

methods for application of the polymeric film. The

first method is a solvent-free process, where the PET

film is thermally laminated (as described earlier for

Ferrolite). The second method uses a PET film to

which a tie layer was previously applied, promoting

adhesion between the PET and the metal surface.

Alternatively, the adhesive may be applied to the

metal surface prior to laminating the polymeric film.

When lacquer is used in one surface, this is applied by

a roller system. The lacquer must be dried and cured

in an oven.

0023 Polymer-coated steel is used for steel aerosol com-

ponents, such as tops, bottoms, and valve cups, but

also for food and beverage applications. In this seg-

ment, it is used for easy-open ends and for containers

such as food trays and drink cans. Food trays in

polymer-coated steel are microwaveable, strong, and

remain rigid when hot. Fabrication of two-piece

drink cans from laminated steel requires specific tech-

nologies, but developments in this area have led to a

considerable growth on the interest for this new type

of cans.

0024The TULC can (Toyo Ultimate Can) and the RBS

can (Redicon British Steel) are examples of this type

of cans. The TULC can is a development of Toyo

Seikan Kaisha, and it has been on the Japanese

market since 1992, currently representing around

14% of the Japanese can manufacturing market.

The RBS can was launched by Corus Packaging Plus

and Redicon Corporation in 1997 (Figure 16). These

are two-piece cans made from PET laminated tin-free

steel, in the TULC case, and from Ferrolite, in the

RBS case. The cans are produced by a draw–stretch–

redraw technique, an improvement on the draw–

redraw process, in which body-stretching operation

is included. The RBS production line includes a mech-

anical body-shaping machine. Recent developments

in the TULC can manufacturing process have led to

the use of wall ironing, which implies considerable

can lightweighting. Another recent innovation in the

TULC can is the new wall design in a triangulated

pattern (the Diacut pattern), which using slightly

more material thus providing a much better resistance

to denting and allowing for a global weight reduction.

The polymer-coated steel cans weigh more than a

regular draw-wall-ironing steel can, but further

weight reductions are expected by producers of

these cans.

0025Polymer laminated steel is also used for three-piece

cans, as the Crystal can from the Japanese producer

Hokkai. In this case, tin-free steel is coated on both

surfaces with PET. The lamination requires an adhe-

sive layer and therefore a curing operation. The sheets

are cut into can body blanks and welded. The exter-

nal layer of PET is preprinted with a high-definition

decoration, providing a very appealing image.

0026An alternative to laminated metal, using a polymer

coating, is extrusion coating. This technology is com-

monly used in other areas of the packaging industry,

such as polyethylene extrusion coating of paper

and paperboard. In extrusion coating, the polymer is

Steel

Pre-heat

steel substrate

Film reel

Film applied to steel

at nip rollers

Post heat

to melt film

(induction heater)

Soak

zone

Quench

Nip

rolls

fig0015 Figure 15 Ferrolite-producing process.

fig0016Figure 16 RBS cans and TULC can. From The CanMaker

Group Ltd. Reprinted with permission.

CANNING/Recent Developments in Can Design 839

extruded and applied, in the melted state as it leaves

the extruder die, on to the metal substrate. Advocates

of this technology claim that, compared with the

laminates, extrusion coating has the following advan-

tages: thinner coatings, a wider range of materials

available, better adhesion and flexibility, and lower

costs. This technology is, however, still under devel-

opment and, besides some unsolved issues such as can

decoration, still lacks consolidation and proven

results at the industrial level.

0027 Alcoa has been developing its Flex-Coat extrusion

coating system, devoted to aluminum coating for

beverage draw-wall-ironed cans. Hoogovens de-

veloped the Protact, a multilayer coated steel intended

for aerosol components, full aperture easy-open ends,

and twist-off caps, although applications in shallow

cans and trays are also expected. The composite has

three layers of polymer on each side of chromium-

coated steel applied by coextrusion. The top layer

provides wear resistance, gloss, and ink adhesion,

the center layer gives strength and coloring, and the

third layer provides adhesion to the metal substrate.

Can Opening

0028 One of the most remarkable features introduced in

metal cans is the easy-open end. Easy opening is

considered by consumers to be a major advantage

and marketing argument for the metal can, and its

rate of use is increasing. Easy-open ends are of two

broad types: those that provide a pouring aperture for

dispensing liquids, used in beverage cans, and those

that give a full aperture to remove solid products,

used in food cans.

0029 The ring-pull easy-open end for drink cans was first

introduced in 1962. The tab was detachable, causing

litter problems. To overcome this, stay-on tabs were

incorporated later on. Easy-open ends for food cans,

full aperture ends, were introduced in 1965. The first

ends were made of aluminum (since this is an easily

workable material), and only in the middle of the

1980s were steel easy-open ends being widely used.

0030 The importance of this feature in selling cans has

led producers to invest great effort and economic

resources in optimizing the concept. Easy-open ends

must accommodate a compromise between easy

opening and resistance during the product’s thermal

processing and can handling during the distribution

operations. Balancing these opposite requirements is

a technical challenge, and the design of an easy-open

end includes several aspects that should be precisely

detailed:

0031 the levering tab (produced separately and attached

to the end) should not be too hard to lift for

breaking the can end (initial pop); the tab ring

should also allow easy access to the consumer’s

finger at the peeling back stage;

0032the rivet formed in the end panel through which the

tab is attached without loss of the end integrity; if

the rivet is not strong enough, when peeling the

end, the consumer might remove the ring without

opening the can;

0033the panel profile that is responsible for the end

behavior both during the thermal processing (pro-

viding the required reversible deformation) and

when peeling off the end; and

0034the score line that allows for the end to be torn off;

the depth of the score line has very tight tolerances,

as it controls the force needed to tear the end off

but also constitutes a weak region of the can.

Current developments and improvements focus on

making ends safer and easier to open (that is avoiding

sharp edges that might hurt the consumer and requir-

ing less effort to open the can) while maintaining the

required mechanical strength and reducing cost by

reducing thickness and diameter.

0035The Eole II from Carnauld Metalbox Food, the Top

Can from Impress and the Meteor from Usinor Pack-

aging are some examples of recent developments in

steel easy-open designs for food cans. The first two

are manufactured from single-reduced steel, and the

last is produced with double-reduced steel.

0036Eole II is an update of the Eole first version, and the

producer claims that improvements in the panel

design and in the score line profile have led to an

end that is 30–40% easier to open, with equal or

better performance in mechanical and seaming load

tests. The initial pop force required is lower, and the

size of the finger well is larger for easier access. The

Eole family of ends is supplied with a printed diagram

on the panel, to inform the consumer of the best way

to open the can.

0037The Top Can follows a different philosophy: in-

stead of reducing the initial pop force, the end is

designed to reduce the amount of energy globally

expended in the opening process (pop plus tear).

The panel profile insures that the end does not bend

during the peeling part of the opening process, which

is claimed to reduce the tearing force. The total

energy expended is reduced, even with an increased

pop force.

0038The Meteor design uses double-reduced steel com-

bined with a new method of producing the rivet. Pro-

ducers claim that this allows for an increased ease of

opening, and for the possibility of reducing the thick-

ness of the end without compromising strength.

0039In the beverage area, Crown Cork & Seal intro-

duced very recently the SuperEnd. This new design is

840 CANNING/Recent Developments in Can Design

claimed to provide a better seam integrity, to be

stronger, to be easier to open and to drink from, and

to have better pouring characteristics. Figure 17 shows

the profiles of the current industry standard and that

of the new end design, before and after seaming.

0040 Other developments in cans opening and closing

systems are resealable drink cans (screw-top cans)

that allow closure between uses, and the peelable

end, where a foil end is heat-sealed to a metal ring,

which is then double-seamed on to the can body.

See also: Canning: Cans and their Manufacture

Further Reading

Baker M and Eckroth D (eds) (1986) The Wiley Encyclo-

pedia of Packaging Technology. New York: Wiley.

Goddard R (1992) Metals in Packaging. Leatherhead, UK:

Pira International.

Page B (1998) Design for the future. The CanMaker

November: 47–48.

Robertson GL (1993) Food Packaging Principles and

Practice. New York: Marcel Dekker.

Soroka W (1995) Fundamentals of Packaging Technology.

Herndon, VA: Institute of Packaging Professionals.

Food Handling

P Rutledge, Food Processing Consultant, NSW,

Australia

Introduction

0001There is a large variety of affordable, canned foods

available on supermarket shelves. These foods com-

prise the full range of the food groups which include

meat, fruit, vegetables, cereals, and dairy products.

Preparation methods and canning technology vary

depending upon the product. Vegetables and fruits are

canned directly after harvest and require washing,

blanching, and sometimes peeling before canning.

Meat, once it is butchered, is cut into chunks or minced,

while cereals are often used as the ground flour.

0002Farm produce is generally seasonal and is only

available for a matter of weeks each year. Canneries

require enough produce during this short time to

maintain stock in the supermarket from season to

season. This means the scale of operation is in tonnes

per hour for sometimes 24 h day

1

to process enough

product while it is available. Mechanical handling

and processing systems are essential under these

conditions.

Preparation of Vegetables

0003Vegetables are normally mechanically harvested.

Mechanical harvesters do not distinguish between

the wanted vegetable material and other extraneous

plant material and soil. Some of this is removed

by fans and belts on the harvester before the crop

is transported to the cannery. Cannery cleaning

operations must be very thorough to removed the

unwanted material and wash the vegetable.

Cleaning

0004The preparation of vegetables harvested from under

the ground, such as carrots and potatoes, requires the

removal of adhering soil and stones. Several systems

are available to remove the soil, and they start with

dry brushing or soaking to remove the bulk of the

dirt, followed by washing. Washing involves wet

scrubbing with rotary brushes or rubber fingers,

followed by rinsing in a rod washer. In the rod

washer, the vegetables are tumbled in a cylinder

made from steel rods while being washed by water

sprays from inside the cylinder. These vegetables

are usually peeled in a subsequent operation, which

insures a clean product.

0005Legumes, such as green peas and beans, are mech-

anically harvested and transported in bulk ready for

SuperEnd beverage end profile

Conventional beverage end profile

fig0017 Figure 17 Recent developments in easy-opening. From The

Group Ltd. Reprinted with permission.

CANNING/Food Handling 841

canning to the processing plant. Specialized equip-

ment is used, for example, to carry out operations

such as husking corn and breaking up clusters of

green beans. Dry cleaning with air blowers to remove

extraneous leaf material from this type of vegetable is

followed by washing in tanks which removes mud

balls and stones. Some systems use froth flotation

cleaners to remove small pieces of vegetable material.

A final rinse with water follows the cleaning treat-

ment to remove the last of the soil.

0006 Leaf vegetables, such as spinach, are difficult to

clean as extraneous material lodges between the

leaves. Leaves are cleaned by floating them in tanks

of water where the water is agitated with air or water

injection. This separates the leaves and removes the

soil.

0007 Inspection of the washed vegetable by instruments,

such as color sorters or electronic sorters, at this stage

will remove any remaining unwanted material.

Manual inspection is still carried out where the

removal of specific material cannot be achieved

mechanically.

Peeling

0008 Vegetable peeling may be by mechanical cutting or

abrasion, by the use of high-pressure steam, or by

chemical treatment. Abrasion peeling uses carborun-

dum-covered rollers or disks which come in contact

with the skin of the tumbled vegetable. The abraded

skin is removed with water sprays. To remove mater-

ial from depressions in the vegetable, some of the

flesh of the vegetable is also removed with abrasion

and, as such, gives the lowest yield of the three

methods.

0009 Vegetables are steam-peeled by holding them for a

short time in high-pressure steam. This superheats a

layer of tissue under the skin. When the pressure

is suddenly released, the tissue explosively boils,

releasing the skin from intimate contact with the

vegetable. Typical conditions for steam peeling are

17 atm steam pressure for about 30 s. The skin is

washed from the vegetable. This system is the most

efficient in removing the skin and in yield of peeled

vegetable.

0010 A hot lye (sodium hydroxide) solution is used for

chemically peeling vegetables and some fruits. It is

important that the vegetable is thoroughly washed

after peeling to remove all traces of the lye. The

treatment varies depending upon the skin to be re-

moved, but a boiling solution of 10% lye will remove

most skins in less than 1 min. The skin is removed by

rotating brushes or rubber fingers and water sprays.

Caustic waste, both liquid and solid, has to be neu-

tralized with acid before disposal, which increases the

cost of peeling.

Slicing and Dicing

0011Cutting operations are used to supply the required

size of vegetable for canning. Asparagus spears are

sawn to the correct length for the can, and carrot and

potato are sliced or diced to give an attractive piece of

canned vegetable. Canned food in which the particles

are of uniform size generally has a superior appear-

ance to that with large variations in particle size.

Some dicers are designed to give an irregular-shaped

dice so the product looks home-made. The size and

shape of the canned vegetable depend upon the style

of pack that the market requires.

Preparation of Fruit

Washing

0012Generally fruit is more easily damaged than vege-

tables. Therefore, fruit is washed by submersion in

tanks of water, which is agitated, followed by water

sprays on the elevators as the fruit is removed from

the tank. Rod washers may be used with fruit, such as

citrus, which are not easily damaged.

Peeling and Pitting

0013Pome and some stone fruit require peeling and pitting

before canning. Pitting is a mechanical operation, and

each type of fruit has specialized equipment designed

for pit removal. Mechanical apple and pear peelers

remove the core section and skin before halving the

fruit. Stone fruit that is peeled for canning is usually

chemically peeled with lye followed by washing.

Other fruit with stems, such as cherries, are rolled

over sets of small rotating rollers which pick up the

stems and remove them.

Blanching

0014Blanching is a heat treatment in a near-boiling water

or steam followed by rapid cooling given to vege-

tables and some fruit. Blanching removes gases from

within the tissue and softens the product. Blanching

makes the product easier to fill into the can and to

obtain the correct fill weight. The removal of the gas

also reduces the oxidation of the product, maintains

the vacuum in the can, and prevents excessive can

corrosion.

0015Blanching gives the product another washing treat-

ment and inactivates enzymes which may cause de-

terioration of the food. Enzyme inactivation is not as

important for canned foods as it is for frozen foods, as

canned foods receive a far greater heat treatment

during thermal processing of the can. It can be im-

portant if there is a long delay between filling the can

and retorting. Typical blanch times in near-boiling

842 CANNING/Food Handling

water are 60–90 s for small objects, such as green peas

and diced carrot, and up to 3 min for larger pieces.

Preparation of Juices

0016 Juices are the liquid which may be squeezed from

fruits and vegetables. The major methods of ex-

tracting juices are to apply a force to the whole or

pulped material followed by screening out pulp from

the resultant liquid. This can be carried out continu-

ously in screw presses and belt presses, and there are

many different types of batch presses. Citrus fruit is

reamed on mechanical reamers or crushed in such a

way as to remove the edible portion from the skin.

Unwanted material is removed from the juice in

paddle or brush finishers, or in some cases small

screw presses. These machines push the juice through

a screen while separating and removing the pulp

which is too large to pass through the screen.

0017 Citrus juice is pasteurized, which is a heat treat-

ment of 95



C, immediately after extraction to inacti-

vate pectinase, which will cause the cloud in the juice

to ‘fall.’ The cloud in the juice is held by naturally

occurring pectin which, when attacked by pectinase,

allows the juice to separate into a clear serum and a

solid deposit. Conversely, pectinase may be added to

other juices, such as apple juice, to manufacture a

clear juice. If the juice is not hot-filled it will receive

another heat treatment during the canning process.

Meat Preparation

0018 Meat preparation, after slaughter and deboning,

mainly consists of removing unwanted tissue such as

fat, skin, and visible arteries. Meat shrinks by about

30% when it is cooked, so for formulated products

using meat it is usually precooked before filling into

the cans. Some meat products are corned, which

means they are cooked with a cure containing salt

and nitrite. Nitrite causes the meat to turn a charac-

teristic pink color during heating and, because of its

antimicrobial action, permits a less severe heat treat-

ment during retorting. (See Curing; Meat: Slaughter.)

0019 Fish such as tuna are cleaned and then steamed to

allow for the easy removal of skin and bones. The

steamed fillets are filled into a machine which shapes

and cuts them to the can size before filling into the

can. Other fish are cut to size and filled raw. Fish are

canned with brine or oil or, in some cases, a formu-

lated sauce. (See Fish: Processing.)

Preparation of Formulated Products

0020 There is an infinite variety of formulated products

from meat stews to dairy desserts, and beverages

such as beer, that are canned. Most of these products

are cooked or blended or brewed prior to filling.

Those that are cooked in the preparation stage are

filled into the can hot.

0021Carbonated products, such as beer and sparkling

fruit juices, are filled at temperatures just above freez-

ing to maintain the carbonation. Soft drinks, al-

though they are often packed in metal cans, are not

‘canned products’ as preservatives are used to main-

tain their microbiological stability. (See Preservation

of Food.)

Cans

0022Cans are delivered to the factory on pallets. The

pallets are automatically unloaded into the can race

system. This delivers the correct-size can to the can

filler. Canning lines operate between 200 and 2000

cans per minute, so this system must work effectively.

Cans may be contaminated so they are thoroughly

washed prior to filling.

Filling

0023There are many types of machines used to fill cans,

and the type employed depends, of course, on the

product to be filled. Volumetric piston fillers can be

used with liquid products and liquid products with

entrained solids, such as mushrooms in butter sauce.

A turntable is used containing several filling ‘heads’ so

that several cans are filled sequentially as the turn-

table rotates; filler speed depends upon the number of

heads. A slow filler might have 12 heads, while high-

speed fillers have up to 72 heads.

0024Tumble fillers are used to fill solid materials, such

as vegetable pieces, into cans. The washed cans move

through a large rotating drum containing the pieces of

product. The product falls into the can and excess is

removed by tilting and shaking the can at the exit of

the filler. Other volumetric fillers wipe the solid prod-

ucts into pockets on a turntable and the products are

then dumped by gravity into the can.

0025Hand filling is used for products that are difficult

to fill by machine. The filling of asparagus into cans

can be carried out by machine but in some cases the

tips are damaged, so some processors prefer hand

filling.

0026Some products are canned with syrup or brine.

This is a separate operation to filling the solid food.

It may take place before or after the filling of the

solids. Some solid products may have pockets of air

held between the pieces and, in these cases, the liquid

is added prior to filling the solids so the liquid will fill

these spaces. Sometimes the cans are topped up after

the solids are filled.

CANNING/Food Handling 843

0027 A head space must be left in the top of the can after

filling. This small space is evacuated on closing, but is

important to the integrity of the can. An overfilled

can prevents the expansion of the product during the

thermal process, which may result in permanent

damage to the can end. Also the thermal characteris-

tics of the can change, which may invalidate the

calculated thermal process.

Exhausting

0028 Oxygen remaining in the head space of cans acceler-

ates corrosion of the tin plate in the head space area.

To prevent this occurring, the volume of gas between

the product and the lid of the can (known as the head

space) must contain a partial vacuum.

0029 The conventional system of exhausting the cans is

to clinch the lid on the can. Clinching is a partial, first

operation seaming roll which holds the lid loosely on

the can. Exhausting is carried out by passing the filled

cans with clinched lids through a steam-filled com-

partment for several minutes to heat the can contents

and displace the air in the can with steam. This is

immediately followed by the completion of the

seaming operation.

0030 Another method of exhausting is by filling the

product hot into the can followed by hot brining or

syruping which has the same effect as steam exhaust-

ing. This is followed by ‘steam flow closing.’ Steam is

injected between the can and the lid as they come

together in the can closer. This displaces the air in

the head-space region. When the steam condenses, a

vacuum is formed in the head space of the can.

0031 Alternatively, mechanical vacuum pumps can be

used to reduce the air in the head space of the can.

This can be done during filling, as fruit may be

vacuum-syruped by pulling a vacuum on the can

and air is replaced by the incoming syrup. Some clo-

sers have a vacuum chamber in which the can is

seamed. This is common in meat and fish canning,

where the canning lines are slowed by the relatively

slow operation of the vacuum closer.

0032 Acid products, such as fruit juices, jams, pickles,

and chutneys, may be filled into the can at near-

boiling temperatures. The cans are seamed, inverted

to sterilize the lid, and then cooled. This is called the

hot-fill process. The vacuum results from the shrink-

age of the product on cooling and the displacement of

air by the steam from the hot product.

Can Closing or Seaming

0033 The modern can closer also has a turntable similar to

the filler where the cans are fed into a closing ‘sta-

tion.’ The lid is aligned over the can and the baseplate

of the station raises the can and lid to engage the top

chuck. The seaming rollers then roll around the seam

to form the seal. The rollers retract, the baseplate is

lowered, and the closed can exits from the closer.

Closers with four to six stations are common.

0034The seaming operation is carried out by two rolling

operations. The first operation roller bends the two

flanges together, and the second operation roller flat-

tens them to form a seal. The seal is insured by a thin

layer of mastic-like material deposited in the flange of

the can end called ‘compound.’

0035Rates of can seaming depend more on the speed of

the filler than that of the can closer. Beverages which

are easy to fill can be closed at speeds of 2000 cans

per minute. New fillers for semisolid foods, such as

pet food, allow closer speeds of about 1300 cans per

minute and vegetables are often closed at 500 cans

per minute.

Thermal Processing

0036There are two important factors in canning which

make the food safe for long-term storage. Food is

sealed to prevent recontamination, and it is heated

to inactivate microbes which spoil the food. The

seaming operation on the can hermetically seals the

food, and the thermal process provides the steriliza-

tion step.

0037Products which have a pH of less than 4.5 are

called ‘acid foods’ and can be thermally processed at

temperatures less than 100



C, which is called a

pasteurization process. Those with a pH above 4.5

are called ‘low-acid foods’ and must be thermally

processed at temperatures between 110 and 125



in a retort or pressure vessel.

Postprocessing Operation

0038Cans exiting from water-cooling operations are wet

with chlorinated water and must be dried before

they can be handled safely. Some canners label the

cans directly after processing and other palletize

the cans for storage before labeling. Lithographed

cans do not require further labeling.

0039Can stores should be maintained at a temperature

designed to prevent water vapor condensation which

could rust the outside of the cans. The temperature

must, however, not be too high as this can, on very

rare occasions, promote the growth of heat-resistant

thermophilic bacterial spores which may have

survived the thermal process.

0040Cans are held by the canner in store until an incu-

bation period has passed. This provides added protec-

tion for the customers as it insures that only safe

wholesome food is placed in the marketplace. All

844 CANNING/Food Handling

cans are packed in cardboard outers to prevent

damage to the cans during transport and handling,

and also as a convenient package for the supermarket.

Storage of Canned Food in the Home

0041 Canned food should be stored in a dry cupboard.

Most canned food is safe for at least 2 years, but

care should be taken to use the oldest cans first.

Stock rotation is important at home as well as in the

supermarket.

See also: Canning: Principles; Curing; Fish: Processing;

Meat: Slaughter; Preservation of Food