Cross-contamination is when a hazard is moved from one place to another — for example, harmful bacteria from raw chicken onto a salad, or traces of nuts into a nut-free dish. It is one of the main causes of food poisoning.
How cross-contamination happens
There are three main routes:
- Direct contact — raw food touches ready-to-eat food, for example in a fridge or on a display.
- Drips — juices from raw meat drip onto food below.
- Indirect contact — through hands, cloths, knives, chopping boards, slicers, probes, containers and work surfaces.
Remember: ready-to-eat food will not be cooked again, so any bacteria that land on it will reach the customer.
Keep raw and ready-to-eat food apart
- Store raw and ready-to-eat food separately. If they must share a fridge, put ready-to-eat food on the top shelves and raw meat, poultry and fish on the bottom, covered, so nothing can drip down.
- Prepare raw and ready-to-eat food in separate areas. If you only have one area, clean and disinfect it thoroughly after raw food and before ready-to-eat food — or prepare ready-to-eat food first.
- Use separate equipment for raw and ready-to-eat food. Many kitchens use colour coding (for example, different coloured chopping boards and knives). Follow the colour system of your workplace.
- In display units, keep raw food and ready-to-eat food separate.
- Wash your hands after handling raw food.
Complex equipment
Some equipment is very hard to clean fully, such as vacuum packing machines, meat slicers and mincers. The FSAI's Safe Catering pack advises that complex equipment used for ready-to-eat food must never be used for raw food. Keep separate machines.
Cloths and cleaning equipment
- Use disposable cloths, or change and wash reusable cloths often.
- Use separate cleaning equipment (cloths, mops, buckets) for raw areas, ready-to-eat areas and toilets — colour coding helps.
Washing food
Wash fruit and vegetables in a sink kept for food, not the wash-hand basin. Do not wash raw chicken or meat — splashing spreads bacteria around the sink and surfaces, and cooking will kill the bacteria anyway.
Handle food as little as possible
Use tongs, spoons, scoops and other utensils instead of hands where you can. Avoid unnecessary touching of food, food contact surfaces and equipment.
Physical and chemical contamination
Cross-contamination is not only about bacteria:
- Keep cleaning chemicals away from food, in their own store, in labelled containers.
- Prevent physical hazards: wear a hair covering, keep jewellery off, report broken glass or damaged equipment, and remove staples and packaging carefully.
- Never place food directly under an insect electrocutor (fly killer).
Allergen cross-contamination
Allergens can also be spread by hands, equipment, oil and surfaces. This is covered in detail in the allergens lesson.
Speak up
If you see something that could cause cross-contamination — raw meat on a top shelf, a shared chopping board, a damaged container — fix it if you can and tell your supervisor.
Common mistakes to watch for
- Using the same knife to trim raw chicken and then slice cooked ham.
- Putting cooked food back on the plate or tray that held it raw.
- Using one probe for raw and cooked food without cleaning and disinfecting it in between.
- Using the same cloth to wipe a raw meat board and then a salad bar.
- Storing a tray of raw burgers on the top shelf above desserts.
- Touching your hair or phone and then garnishing plates without washing your hands.
In practice
In a pub kitchen, the chef prepares raw chicken goujons on a red board, then wipes the board with a cloth and uses it to cut tomatoes for burgers. The tomatoes will not be cooked.
The board and the cloth now carry bacteria from the raw chicken onto a ready-to-eat food. The correct practice is to use the board colour kept for salad and vegetables (or a fully cleaned and disinfected board), a clean knife, a clean cloth, and to wash hands after handling the raw chicken.
Ask yourself at each step: "Could this food, surface, tool or my hands carry something from raw to ready-to-eat?" If the answer is yes, separate, clean or wash first.