Microbes and food 4. Food spoilage - preserving food
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4.5 Stopping the rot - other treatments
Bacon photo
Picture 4.5a Bacon is an example of a cured meat.

Chemicals
Preservatives may be added to food to protect it against microbial action. Some of these additives, such as curing, pickling & fermenting, are not new.

Curing pork with nitrites and salt produces bacon and ham. The chemicals dry the surface and draw water out of the meat, inhibiting the growth of bacteria.

Pickling & fermentation are ancient methods of preservation using acids. The acetic acid in vinegar stops microbial spoilage of chutneys and sauces. The lactic acid in yoghurt, fermented meats and vegetables slows the growth of yeasts and mould.

Sulphur dioxide is effective against bacteria, yeasts and moulds in fresh sausages and wine.

Benzoic acid, ascorbic acid and proprionic acid are also common commercial food preservatives.

These days, the use of chemicals to prevent food spoilage is not favoured by the public and it is carefully controlled by law. It is only the introduction of new technologies, such as refrigeration and canning, that have made a reduction in the use of preservatives possible.

Dried pasta photo
Picture 4.5b Pasta can be stored for a long time once it has been dried.

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Drying
This is an ancient method of preserving foods. Removing moisture prevents the growth of microbes. Dried foods, like pasta and flour, will keep for a long time in damp-free storage.
Freeze drying
Foods like liquid coffee, fruits and meat are quick frozen to produce small ice crystals in the cells. They are then put in a vacuum so that the ice evaporates. Bacteria can survive this process but the freeze dried product is generally hostile to microbial growth.
Packaging
Wrapping a food can stop it getting contaminated by microbes. In addition, by choosing the type of packaging and the gases inside it, existing microbes can be slowed or prevented from growing.
Irradiation
Firing gamma rays at food can kill microbes. If it is done carefully, the radiation doesn’t affect the flavour or structure of the food. There is considerable consumer resistance to irradiation and it is only permitted for a few foods in the UK.