Filling and Sealing Packaged Foods
Practical Action
Hermetically sealed glass jars or metal cans that are used for bottled or canned foods are not
filled completely. A ‘headspace’ is needed above the food to form a vacuum when it cools. When
filling solid foods or pastes, it is necessary to prevent air from becoming trapped in the product,
which would reduce the headspace vacuum. Viscous sauces or gravies are therefore filled before
solid pieces of food. This is less important with dilute brines or syrups, as air is able to escape
more easily before sealing (see also Technical Briefs: Packaging Foods in Glass and Canning of
Foods).
Sealing
Different types of closures for plastic and glass containers include metal or plastic caps and lids,
and foil, plastic or paper covers. It is not possible in this Technical Brief to describe each of these
closures in detail. In practice the selection of a package and closure depends mostly on their local
availability and relative cost. The choice of packaging may therefore be a compromise between what
is required and what is available/affordable, the penalty being a reduction in shelf life of the food.
Pilferage and tampering
Although total protection is not possible, tamper-resistant packaging delays entry into the
package and tamper-evident packs indicate whether tampering has been attempted or has
occurred. The main use of tamper resistance/evidence is for bottles, pots and jars that enable
consumers to use the contents a little at a time and therefore need to be re-closable. Examples
of tamper-evident or tamper-resistant closures are shown in Table 1.
Table 1. Tamper-evident / -resistant packaging
Type of packaging Tamper-evident or tamper-resistant features
Bottles and jars Foil or membrane seals for wide-mouthed plastic pots and bottles
(glass or plastic)
Heat-shrinkable plastic sleeves for bottle necks, or bands or
wrappers placed over lids. Perforated plastic or paper strips that
must be cut or torn to gain access
Breakable rings or bridges to join a bottle cap to a lower section
(the container cannot be opened without breaking the bridge or
removing the ring)
Roll-on pilfer-proof (ROPP) caps for bottles (during rolling, a
tamper-evident ring in the cap locks onto the bottle neck. A seal
breaks on opening and the ring drops slightly)
A safety button in lids for heat sterilised jars (a concave section
formed in the lid by the headspace vacuum becomes convex when
opened)
A breakable plastic strip that shows if a jar has been opened
Flexible films
Film must be cut or torn to gain access
Blister or bubble packs that show if the backing material has
been separated from blisters.
Laminated plastic/foil pouches must be cut to gain access
Tubes (aluminium Foil membrane over tube mouth that has to be punctured to gain
or plastic)
access
Cans
Steel or aluminium cans are inherently tamper-resistant (see also
Technical Brief: Canning of Foods)
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