Every year, an estimated 5.4 million Australians contract a food-borne illness - and biological contamination is behind most of these outbreaks. Unlike chemical contamination (from chemicals like cleaning products) or physical contamination (from foreign objects like glass), biological contamination happens when food is contaminated by bacteria or other microorganisms. It's invisible, it's everywhere, and it's the single biggest food safety risk any food business faces.
For anyone working in a commercial kitchen, understanding how biological contamination happens, and what conditions let it thrive, is the first step to preventing it.
There are six types of microorganisms that can cause food-borne illness: bacteria, viruses, parasites, protozoa, fungi and prions. Of these, bacteria are by far the most common culprit.
Bacteria are found everywhere in a commercial kitchen - on food, surfaces, equipment and even staff themselves. They're also alarmingly efficient at multiplying: bacteria reproduce by splitting themselves in two, and a small number can become millions within just a few hours. Worse still, you can't see, taste or smell most bacteria, which means contaminated food can look and taste completely normal.
Bacteria need the right environment to multiply to dangerous levels. Food Handlers who understand these six growth conditions are far better equipped to control the risk.
Like any living organism, bacteria need food to survive. They can grow on almost anything, but thrive especially on foods high in protein - meat, seafood and dairy. Food-borne illness outbreaks have also been linked to less obvious foods such as cooked rice, rockmelons and packaged salad items.
Acidity is measured on the pH scale, from 1 (most acidic) to 14 (most alkaline). Pathogens grow rapidly on foods with a pH over 4.5, and grow best on neutral foods between 6 and 8.9. This is why lemon juice - with a pH of 2 to 3 – is often added to foods to discourage bacterial growth.
Bacteria multiply most rapidly within the Temperature Danger Zone, which sits between 5°C and 60°C. The longer food sits within this range, the greater the risk of food-borne illness, which is why food should be stored quickly after receiving and handled in small batches wherever possible.
Most harmful bacteria are aerobic, meaning they need oxygen to survive. A smaller number, known as anaerobic bacteria, can survive without oxygen at all - which is why it's still possible to contract a food-borne illness from canned goods.
Bacteria need water to grow, which is why preservation techniques like salting and drying have long been used to make food safer. The reverse is also true: adding moisture back into dried goods can make otherwise safe food hazardous. Cooked rice, for example, is considered high-risk, while uncooked rice isn't.
The longer food is exposed to favourable conditions, particularly time spent in the Temperature Danger Zone, the higher the risk that bacteria will multiply to unsafe levels.
Not all foods carry the same level of risk. High-risk foods - sometimes called potentially hazardous foods - are those with ideal conditions for bacterial growth: typically low in acid, high in starch or protein, and moist. Common examples include dairy, eggs, red meat, poultry, fish and shellfish, cooked rice and pasta, and processed fruits and vegetables such as ready-to-eat salads.
Low-risk foods, by contrast, don't offer the same conditions for bacteria to thrive. These include high-acid foods, salted foods, dry foods, canned or vacuum-packed foods, and high-sugar foods such as crackers, biscuits, plain bread, uncut fruit and vegetables, pickles, and jams.
Knowing which category a food falls into helps determine how carefully it needs to be stored, handled and monitored.
It's worth distinguishing between food spoilage and biological contamination. Food spoilage occurs when there's a disagreeable change in the normal state of food - mould appearing on fruit is a classic example. When spoilage is caused by harmful bacteria that make food unsafe to eat, it's known as pathogenic spoilage. Not all spoiled food is dangerous, but all pathogenic spoilage is a biological contamination risk.
Controlling biological contamination comes down to managing the six growth conditions wherever possible: keeping high-risk foods out of the Temperature Danger Zone, minimising the time food spends at room temperature, maintaining strict hygiene around surfaces and equipment, and storing food correctly as soon as it arrives.
This is exactly the kind of knowledge a Food Safety Supervisor is trained to apply day to day - identifying where contamination risks exist in a kitchen and putting the right controls in place before they become a problem.
A Food Safety Supervisor plays a critical role in managing biological contamination risk - from spotting high-risk foods to keeping temperature control front of mind across a busy kitchen. Start your Food Safety Supervisor course today with the Australian Institute of Food Safety (AIFS) and build the skills to keep your workplace food safe and compliant.
Q. What is the most common cause of biological contamination?
A. Bacteria are the most common cause of food-borne illness. They're found throughout domestic anf commercial kitchens and can multiply from a small number to millions within hours under the right conditions.
Q. What is the Temperature Danger Zone?
A. The Temperature Danger Zone is between 5°C and 60°C - the range in which bacteria multiply most rapidly. Minimising the time food spends in this range is one of the most effective ways to reduce biological contamination risk.
Q. Can biological contamination happen in canned or vacuum-packed food?
A. Yes. While most harmful bacteria need oxygen to survive, anaerobic bacteria can grow without it, meaning canned and vacuum-packed goods aren't automatically risk-free.
Q. What's the difference between food spoilage and biological contamination?
A. Food spoilage is any disagreeable change in food's normal state, such as mould. When that spoilage is caused by harmful bacteria that make the food unsafe to eat, it's classified as pathogenic spoilage - a biological contamination risk.