It is commonly believed that when you use alcohol in cooking all of the alcohol is burned off. In general people believe that the processes of cooking mean that none of the alcohol remains in the dish, only the flavor of the alcohol.
The reality is that the amount of alcohol that remains in the food varies greatly depending on time cooked and many other factors. Studies done on the alcohol remaining in food varied widely.
On the high end, 85% of the alcohol remained in the food, and that was when the food was prepared by adding alcohol to a boiling liquid and removing it from the heat. By cooking a food for about two and a half hours you can burn off about 95% of the alcohol, but it’s still likely that you have a small amount of alcohol still remaining.
It seems like the best way to ensure you have absolutely no alcohol would be cooking if for three or more hours! Although, you may be able to cut down on this time slightly by using a larger pan, which gives the alcohol a greater surface area to evaporate from.
For people who don’t drink alcohol for ethical or religious reasons or for parents, this is a significant finding. People might accidentally be getting alcohol from dishes they believed no longer contained alcohol!