Berkel 17074-0 Instructions Sur Le Fonctionnement page 44

ABOUT VACUUM PACKING
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. 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, 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 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 health-threatening.
Several enzymes found in foods cause increasingly 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.
HOW TO PRESERVE FOOD IN BAGS
Vacuum packing for the freezer
First of all, use the freshest possible food. The system will allow you to retain all the freshness of the
food only if it is properly preserved. Some foods have a soft consistency which could be damaged by
vacuum packing the product when fresh. To prepare delicate foods like meat, fish, berries, bread, etc.,
it is advisable to pre-freeze them first. In the first twenty-four hours there is no risk of freezer burns, so
you can vacuum pack the products frozen the previous day in bags, and then keep them in the freezer
for long periods so as to preserve all the nutritional values and flavour of the product you have packed.
When vacuum packing soups, stews or other liquid food, pre-freeze it in a pan or high-strength dish.
When the food becomes solid, vacuum pack it, add a label and replace in your freezer. To vacuum pack
vegetables, peel them and then blanche them briefly in boiling water or a microwave oven until they are
warm but still firm. Then vacuum pack them in convenient portions. If the food is not pre-frozen, leave
an extra 5 cm in the length of the bag to allow for expansion due to freezing. With regard to meat and
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