There's a thread on the food website Chowhound, called 'Refused to Eat, Out of Line?' The poster explains he was at a friend's house for dinner. The friend started cooking hamburgers at 3pm, realised it was early, left the partially cooked burgers at room temperature then resumed cooking them 21/2 hours later. The poster refused to eat the burgers, telling the host that 'there were more reliable ways to poison his friends'. Leaving the etiquette debate behind (because I would have done the same, although with another, more polite, excuse), food poisoning can be extremely unpleasant - even deadly - and it's a cook's responsibility to try to avoid it. Most of us know to throw away refrigerated items that have fuzzy green mould on the surface, or sour-smelling milk. But contaminated foods don't always look or smell bad; some pathogens, such as botulism, salmonella, cholera and E coli, give no indication of their presence. Leaving food at room temperature does not necessarily mean you'll get food poisoning. The reason we put eggs and butter in the fridge isn't because they'll go off if left at room temperature, but that they keep better and longer in the fridge. Other ingredients, such as meat, seafood, milk and fruit juices, can spoil within a few hours if left at room temperature - and the warmer it is, the quicker the ingredients will deteriorate. Bacteria multiply rapidly between the danger zone of four and 60 degrees Celsius. Raw foods that are normally refrigerated shouldn't be left at room temperature for too long before being cooked. Leftover cooked foods should be wrapped then refrigerated as soon as the meal is over. Food not normally prone to bacteria can become cross-contaminated if, say, it is cut on an unwashed cutting board that was used to slice raw chicken. Some people have cutting boards for specific purposes: they reserve one for raw fruit and vegetables, another for raw meat and seafood and one more for cooked food. These are nice to have but not necessary as long as you thoroughly scrub the same board with hot water and dish detergent between each use. Raw and cooked foods should be refrigerated in separate containers. People tend to blame cases of food-borne illness on meat and seafood but it occasionally comes from contaminated vegetables such as radish sprouts and spinach. All vegetables and fruit should be rinsed under cold, running water, even if the package says the contents are 'pre-washed'. And if you're unsure if a food is good or bad, remember the mantra culinary students are taught in their food sanitation class: 'If in doubt, throw it out.'