The Temperature Danger Zone

Zoli asked for more details on the Temperature Danger Zone (TDZ), so here it is - A primary focus in food safety is the control of bacteria. Foods become potentially dangerous when they are allowed to meet the criteria for breeding bacteria. Bacteria need the following to thrive:

F - food
A - acidity (appropriate pH levels, between 4.5 and 7)
T - temperature

T - time
O - oxygen
M - moisture

Bacteria love FAT TOM, so we try to eliminate as many factors as possible when storing foods. Unfortunately there isn't much we can do about their food source, as they're on food. Acidity depends on the product you're cooking. Oxygen is generally present, as is moisture. That leaves us with time and temperature.

Most bacteria grow best between 41 degrees Farenheit and 140 degrees Farenheit (some are resistent to cold and heat so these numbers do not apply, but they are a good general rule). They need approximately 20 minutes to replicate. Bacteria are practically always present, but letting them replicate to the point where their numbers become dangerous can be avoided. 2 hours of bacteria growth is considered the limit for keeping food safe.

So, when we put this all together, we end up with the Temperature Danger Zone - you cannot have foods in the unsafe temperature range for more than 2 hours. When you chill a cooked product, it should not take more than 2 hours to go from 140 to 41. The same is true for warming a food up. Also, a food should not pass through the TDZ more than 3 times, including initial preparation.

This might bring up more questions, but I hope it at least gives you some answers.