Preserving Food

The greatest threat to the quality and safety of our food comes from microbial spoilage. Food is a valuable source of nutrients for certain microbes. As they grow on the food, they may cause problems such as bad taste, unpleasant smell and poor appearance. More importantly, the growth of microbes may lead to dangerous levels of toxins in the food. This makes the food unfit to be eaten.

Smoked fish

Smoking fish is a traditional method of preservation

The greatest threat to the quality and safety of our food comes from microbial spoilage. Food is a valuable source of nutrients for certain microbes. As they grow on the food, they may cause problems such as bad taste, unpleasant smell and poor appearance. More importantly, the growth of microbes may lead to dangerous levels of toxins in the food. This makes the food unfit to be eaten.

Reducing the growth of microbes

Many methods of food preservation are used. Processes such as freezing, canning, pickling and drying all attempt to remove one or more of the factors necessary for the growth of food-spoiling microbes.

Methods of Food Preservation
Preservation How it Works
Canning Foods are sealed into cans and then heated to a high temperature (above 100°C). This kills any microbes in the food and the sealed can prevents fresh contamination
Freezing / chilling Lowering the temperature slows enzyme activity in the food spoiling microbes. This slows cellular respiration and therefore growth. The colder the temperature, the slower the growth. However, microbes are not killed when they are chilled. Foods heated up may still contain microbes that are alive and need to be thoroughly cooked before being eaten
Drying Removes water from the food and so dehydrates the microbes. This prevents their growth but does not remove any toxins that may already be present
Pickling Vinegar is acidic and lowering the pH of the food can prevent the growth of microbes. The acidic environment reduces the enzyme-activity of the food-spoiling microbes
Jam-making Jams contain high concentrations of sugar. This effectively draws water out of any microbes in the food and dehydrates them. This method of preservation is traditionally used to make jams
Smoking Possibly the oldest known method of food preservation. Foods are hung in wood smoke and chemicals in the smoke act to kill microbes in the food and also give it a distinctive flavour. This ancient method survives into our modern times. Some meat, particularly bacon, and fish, such as haddock and salmon, are smoked
Preservatives Some methods of preserving food depend on the use of additives. These substances reduce the growth of microbes but must not be seen as an alternative to proper food hygiene and cooking. Preservatives play their part in clean and hygienic methods of food production

Read more on the application of preservatives