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< prev - next > Food processing Preserves KnO 100259_Bottle and jar cooling system (Printable PDF)
Many food products, such as jams, drinks and sauces, are hot filled into glass containers directly
after cooking or pasteurisation. Unlike tin cans, hot glass cannot be directly placed into cold water
to cool for fear of breakage due to thermal shock. Forced cooling of such hot filled foods is,
however, generally recommended to reduce changes in product colour and flavour. Some products
are much more sensitive than others to changes of this type.
In many small-scale production units, hot containers are simply allowed to air cool and this may take
several hours. The situation is often made worse, in that in order to save space, the bottles are piled
into stacks and so cool even more slowly.
In larger manufacturing plants, hot, closed bottles are passed through continuous coolers in which
they meet zones of water sprays of gradually reducing temperature, thus overcoming the problem of
thermal shock. Such coolers are large, complex and expensive.
A simple, cheap system was developed
in the St Vincent Ministry of
Agriculture's Production Unit to allow
controlled cooling of both bottled fruit
drinks and jam jars, with production
rates being typically 50 to 150 packs
per hour.
The basic system, see Figure 1,
consists of a long water tank set-up in
such a way that it automatically
develops zones of different
temperature along its length, or a
temperature gradient. The tank was
constructed from galvanised iron sheet
and was supported in an angle iron
cradle. The total length was 12ft and
the width, in order to accommodate
the largest bottle used was 13 inches.
Figure 1: Bottle cooling system
The base of the tank was sloped to
increase the depth of water from 0-8 inches along the length.
Mains water was fed continuously to the deep end of the tank, together with a controlled drip of
chlorine solution. The use of chlorinated water for bottle cooling is essential because when a hot
filled pack is first capped, the seal is never perfect. As the pack cools, the glass and the metal cap
seal firmly together and an internal vacuum forms. In effect, this means that in the early stages of
cooling the outside medium, whether it is water or air, can be sucked into the container by the
gradually forming vacuum.
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