Food Hygiene - Bacteria
Bacteria, otherwise known as germs are so small, they are impossible to see without a microscope. Bacteria are everywhere and play an important part in our everyday life.
Important Food Poisoning Bacteria
Clostridium Perfringens
Staphyloccus Aureus
Campylobacter
Bacillus Cereus
Salmonella Species
E. Coli
Most bacteria are harmless and some even benefit us, for example the bacteria in our gut help break down the food and aid digestion and without bacteria food items such as cheese and yoghurt could not be made.
Different bacteria can cause food to smell, lose texture and flavour and generally to decay. These are known as food spoilage bacteria and play an important role by decomposing dead vegetables and animal matter, thus aiding the recycling process.
Organisms that cause diseases are called pathogens. Such germs in food, often in relatively small numbers can cause serious illnesses for example typhoid fever.
Spores
Some bacteria are capable of forming protective coverings and in this state are called spores. They can survive normal cooking temperatures and remain dormant for many years or until suitable conditions return. Should the environment become more suitable, the protective cover will disappear and the bacteria will once again be present to multiply. A temperature of atleast 122C is required to kill spores.
How bacteria grow
In order for bacteria to grow they must have the following four conditions
FOOD MOISTURE WARMTH TIME
Food
Certain food, most of which have a high protein content are particularly rich in nutrients and contain moisture and therefore provide excellent conditions for bacterial growth if kept in warm conditions. When these foods are ready to eat without any further treatment such as cooking which would kill bacteria then these are known as ‘high risk foods’
Examples of high risk foods are….
Cooked meat and poultry
Cooked meat products
Gravy
Stocks
Diary
Milk, eggs and foods containing these products i.e. mayonnaise
Shellfish
Mussels, oysters, prawns, crabs or lobsters may eat food that is contaminated from polluted water so the bacteria can live inside the shellfish as well as on the shells.
Cooked Rice
Bacterial spores can be found in dry rice; once water is added to the rice the bacteria becomes active.
Foods containing sugar, salt or acid i.e. jams or pickles discourage the growth of bacteria. Some foods have preservatives (chemicals) added to them to restrict the growth of bacteria.
Warmth
The ‘danger zone’ as it is commonly referred to is the temperature that bacteria will grow in.
The danger zone is 5 – 63 degrees Celsius, growth will vary depending on the actual temperature but the optimum is 37 degrees which is also the normal temperature of the human body.
Most bacteria are killed by heat once they reach a certain pint and are held at that heat for a minimum period of time. The main exception here is spore forming bacteria which are not killed until they reach a higher temperature.
In the cold bacteria do not die but grow very slowly, at very low temperatures some bacteria may die but the most will survive and continue to grow once again as the temperature increases.
Time
Given all of the other conditions bacteria just need time to grow and not much at that, it is quite often carelessness that allows them the time they need, for example improper cooling of food allowing it to remain in the danger zone for too long.
The correct term for the multiplication of bacteria is Binary Fission, this is where one cell splits itself into two and so on and so on. In optimum conditions this multiplication will take place every 10 to 20 minutes.
Potentially this means after a few hours the one bacterium could have reached the thousands and it is unlikely that just one bacteria would have been present so the numbers would be a great deal higher!
Food poisoning bacteria are invisible to the naked eye and have no effect on taste or smell of the food, therefore your senses cannot be relied upon.
Finished? Try some sample test questions here. (Answers can be found in the download section)