Temperature is the key element. The USDA guidelines for food safety are as follows.
Keep Hot Food Hot
After cooking meat and poultry on the grill, keep it hot until served — at 140 °F or warmer.
Leaving food out too long at room temperature can cause bacteria (such as Staphylococcus aureus, Salmonella Enteritidis, Escherichia coli O157:H7, and Campylobacter) to grow to dangerous levels that can cause illness.
Bacteria grow most rapidly in the range of temperatures between 40 °F and 140 °F, doubling in number in as little as 20 minutes. This range of temperatures is often called the "Danger Zone."
Keep hot food hot — at or above 140 °F. Place cooked food in chafing dishes, preheated steam tables, warming trays, and/or slow cookers.
Keep cold food cold — at or below 40 °F. Place food in containers on ice.
Keep cooked meats hot by setting them to the side of the grill rack, not directly over the coals where they could overcook. At home, the cooked meat can be kept hot in an oven set at approximately 200 °F, in a chafing dish or slow cooker, or on a warming tray. Keep Food Out of the "Danger Zone" Never leave food out of refrigeration over 2 hours. If the air temperature is above 90 °F, food should not be left out more than 1 hour.
Serving the Food
When taking food off the grill, use a clean platter. Don't put cooked food on the same platter that held raw meat or poultry. Any harmful bacteria present in the raw meat juices could contaminate safely cooked food.
In hot weather (above 90 °F), food should never sit out for more than 1 hour.
Leftovers
Refrigerate any leftovers promptly in shallow containers. Discard any food left out more than 2 hours (1 hour if temperatures are above 90 °F).
References:
http://www.fsis.usda.gov/wps/portal...food-handling/danger-zone-40-f-140-f/CT_Index
