What is vacuum sealing?
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 sealing 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, rstly through a process of oxidation, causing the loss of
nutritional values, avour 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 sealing 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 sufcient
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.
Refrigeration 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, sh, seafood, olives in brine, eggs, mushrooms and vegetables) and medium
acidity foods like virtually all vegetables and many fruits (ripe tomatoes, onions, red pepper, gs
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.
Several enzymes found in foods cause increasingly noticeable changes in colour, structure
and avour; 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 briey 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-sealed or frozen, and they can develop during preservation and thus contaminate
the food. Some products like our and grain might contain larvae, but using vacuum sealing will
stop them developing into insects.
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