Filling and Sealing Packaged Foods
Practical Action
Plastic bottles can have a variety of closures that have a pouring spout to dispense the contents.
For example, caps can have a hinged top that reveals a dispensing opening in the cap. They are
used for sqeezeable bottles (e.g. for creams, oils, sauces, mustard, mayonnaise or syrups).
Pot sealers
A semi-automatic heat sealer is available for sealing film lids onto plastic pots at up to 100 pots
an hour, but it is expensive and requires a source of compressed air. A cheaper and simpler
sealer (Fig. 9) is available which will seal about 60 pots/hour. Alternatively an electric iron can
be fitted to a suitable stand (e.g. a drill stand) and pressed down onto the surface of the pots to
seal the film. Plastic trays are sealed with a plastic film or foil laminate (see Technical Brief:
Packaging Materials for Foods) that is heat sealed to the top flanges of the tray. Narrow-necked
ceramic pots may be sealed with a cork stopper covered with candle-wax or beeswax.
Fig. 9. Pot sealer
Wide-mouthed plastic pots and tubs or glass jars can be sealed by a range of different closures,
including push-on, snap-on or clip-on lids (e.g. tubs for margarine or ice cream), and push-on or
crimp-on metal or plastic caps (e.g. for nuts and snackfoods). These closures are not tamper-
resistant, but containers can be fitted with tamper-evident aluminium foil or plastic membranes
(e.g. yoghurt pots). Where a product is to be used over a period of time, or where additional
protection is required for the membrane, a plastic clip-on lid may also be fitted to the pot. Rigid
plastic or cardboard tubs for dry products can have a lid that opens so that the contents can be
poured or shaken from the pack (e.g. small cardboard tubs for salt or spices). These ‘disc top’
closures have a plastic disc that is flipped up to reveal an opening.
Special equipment is needed to seal metal cans (see Technical Brief: Canning of Foods)
Sealing pouches, bags and sacks
Plastic films
Most plastic films are heat sealed but cold seals (adhesive seals) are sometimes used for heat-
sensitive products (e.g. chocolate, chocolate-coated biscuits or ice cream). To seal flexible films,
the two surfaces of the film are heated until they partly melt and pressure is used to fuse the
films together. The strength of the seal depends on the temperature, pressure and time of
sealing. Although it is possible to seal plastic bags by folding the film over a used hacksaw blade
and fusing it with a flame, the quality of the seal is variable and less attractive than using an
electric heat sealer. A better (and faster) option is to use an electric bar-type heat sealer (Fig.
10). If electricity is not available, it is possible to
modify the sealer to heat the bar directly with a flame.
A broader seal is formed with this equipment, which
has better barrier properties and appearance. Sachets
can be made by either buying film in the form of a
tube, or by cutting the film and sealing the long side
to make a tube. One end is sealed and foods are filled,
before sealing the second end. It is important that
foods do not stick to the inside of the pack where the
seal is to made because they prevent a proper seal
from forming or reduce its strength.
Fig. 10. Bar sealer for plastic film
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