What Is Biological Contamination and Why Do You Need to Prevent It?

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.

What causes biological contamination?

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.

The six conditions bacteria need to grow

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.

1. Food

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.

2. Acidity

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.

3. Temperature

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.

4. Oxygen

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.

5. Moisture

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.

6. Time

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.

High-risk vs low-risk foods

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.

Food spoilage vs biological contamination

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.

How to reduce the risk of biological contamination

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.

Ready to build this knowledge into your role?

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.