Cross-contamination

Cross-contamination is when harmful bacteria spread from one food to another, usually from raw meat, poultry, seafood or eggs to food that will not be cooked again. Bacteria such as Salmonella, Campylobacter and E. coli move on hands, boards, knives, cloths and dripping juices. The same idea applies to allergens: a trace of peanut, milk or gluten on a spoon can cause a reaction. In the US this is often called cross-contact. Cooking kills bacteria but does not destroy allergens, so only cleaning removes them.

How to do it

1. Wash your hands with soap and warm water for at least 20 seconds before cooking and after touching raw meat, fish, eggs or unwashed vegetables.
2. Use separate boards for raw meat and for ready-to-eat food, or prepare ready-to-eat food first and wash the board well before raw meat.
3. Store raw meat and fish covered on the bottom shelf of the fridge, so juices cannot drip onto other food. Thaw it there too.
4. Do not wash raw chicken or other meat. Splashes spread bacteria around the sink. Cooking to a safe internal temperature kills them.
5. Use a clean plate and clean tongs for cooked food, not the ones that held it raw.
6. Do not use marinade from raw meat as a sauce unless you boil it first.
7. Clean as you go with hot, soapy water, and change dishcloths and towels often.

For allergens, also wash hands with soap and water, use clean utensils and pans, cook the allergen-free dish first, and keep it covered.

Common mistakes

• Using the same tongs for raw and cooked meat on the grill.
• Cutting salad on a board you just used for raw chicken.
• Wiping up meat juices and then drying dishes with the same cloth.
• Frying allergen-free food in oil used for battered fish or shrimp.
• Relying on hand sanitizer gel alone. It does not remove food allergens.

In recipes

Recipes rarely say "avoid cross-contamination", but they assume you do. Steps such as "transfer to a clean plate" or "wash the board" are there for this reason. If you cook for someone with a food allergy, check the EU 14 allergens or the US major allergens in every ingredient, and ask them what level of care they need.