Hillers Packed lunches are often kept at room temperature for 4-6 hours. Foods which will be kept at room temperature need to be selected and handled carefully to prevent food poisoning. Bacteria are extremely small living organisms. In addition to temperature, the rate of bacterial growth depends on moisture content and acidity.
Bacteria can grow rapidly in moist, low-acid foods such as eggs, milk, meat, fish, and poultry.
There are two ways to keep a packed lunch safe to eat. One is to choose foods which may safely be kept at room temperature because food-poisoning bacteria do not grow in them. The other is to keep the bacteria count low by careful handling of foods. Safe Foods Bacteria do not grow in foods that are high in acid or low in moisture. How to Keep the Bacteria Count Low Perishable foods can be kept safe to eat if they are handled in a way that keeps the bacteria count as low as possible.