Conventional wisdom says that alcohol added to a dish gets cooked away, but in fact, a large percentage of alcohol still remains in the dish, depending on your cooking method, according to a study from the USDA's Nutrient Data Laboratory.
Cooking site Ochef lists the study results showing the per cent of alcohol retained for different preparations. A dish with alcohol added to it but not heated and stored overnight retains 70 per cent of the alcohol, which is still less than a dish where alcohol is added to boiling water and then removed from heat (85 per cent alcohol retained). Baking or simmering for 15 minutes, with the alcohol stirred in, retains 40 per cent of the alcohol.
Although the small amount of alcohol used when cooking isn't a big deal for most people, if you're trying to avoid alcohol for some reason, this is pretty significant. Dishes baked or simmered for two and a half hours or more retain the least amount of alcohol (5 per cent). You can view the full chart on Ochef.