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The deterioration of food is caused by chemical
reactions that occur in food which is exposed
to the air, temperature, moisture, the action
of enzymes, the growth of micro-organisms or
contamination by insects. Vacuum packing
reduces the absolute pressure of the air inside
the package or container, by removing the
oxygen and eliminating volatile compounds.
The oxygen in the air causes food to deteriorate,
firstly through a process of oxidation, causing
the loss of nutritional values, flavour and all
the food’s qualities. Air also promotes the growth
of most micro-organisms and causes the frost
burns which occur on frozen food. Vacuum
packing extends the shelf life of many fresh
foods, by reducing oxidation and preventing
the proliferation of microbes (bacteria and
mould). However, many fresh foods contain
sufficient moisture to encourage the growth
of micro-organisms that can grow with or
without air. To prevent the deterioration of
such foods, they must be preserved at low
temperatures.
Micro-organisms like mould, yeast and bacteria
are present everywhere, but they can cause
problems only in certain conditions. For example,
mould will not grow in environments with a low
oxygen content, or in the absence of moisture
or humidity. To grow, yeast requires moisture,
sugar and a moderate temperature, but it can
grow in the presence or absence of air. Refriger-
ation slows the growth of yeast and freezing
blocks it completely. Bacteria can multiply with
or without air, depending on their type. Clostridium
Botulinum is a very dangerous type of bacteria
which can develop in environments which do
not contain acids, are without oxygen and are
exposed to temperatures in excess of 4°C for
long periods of time. Foodstuffs vulnerable
to attack by Clostridium Botulinum are those
with low acidity (like red meat, poultry, fish,
seafood, olives in brine, eggs, mushrooms and
vegetables) and medium acidity foods like
virtually all vegetables and many fruits (ripe
tomatoes, onions, red pepper, figs and cucumbers).
To prevent contamination by this bacterium,
it is essential to observe the basic rules of
hygiene and, to prevent its harmful proliferation
in preserved foods, they must be refrigerated
for short periods and/or frozen for long-life
preservation. However, such foods must be
eaten immediately after heating.
IMPORTANT:
You must consume immediately
any food which has been heated while still
sealed in Espressions MAGIC VAC® bags.
Leaving the food to cool slowly at room
temperature in the sealed vacuum bag may
cause several harmful micro-organisms to
multiply, in just a few hours, to values that are
healththreatening.
Several enzymes found in foods cause increas-
ingly noticeable changes in colour, structure
and flavour; such changes depend on the
preservation time, temperature and, above
all, the presence of air. To halt the action of
enzymes, vegetables must be blanched briefly
using steam or a microwave oven. Food which
contains a high percentage of acidity, like most
fruits, do not require blanching. The absence of
air created by the vacuum will in any case slow
down or prevent the action of these enzymes.
Insect larvae are frequently found in many
low water content or dried foods which have
not been vacuum packed or frozen, and they
can develop during preservation and thus
contaminate the food. Some products like
flour and grain might contain larvae, but using
vacuum packing will stop them developing into
insects.
About vacuum packing
Summary of Contents for EP6400
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