Amount of alcohol burning off is dependent on the temperature and the size of the pan. Hotter temperatures will burn off more alcohol, as would a larger pan. Remember that after 30 minutes of boiling, the alcohol concentration drops by 10% for every half-hour of cooking after that, up to 2 hours. That implies boiling alcohol down to 35 percent takes 30 minutes, and an hour of simmering reduces it to 25 percent. You'll be down to 10% after two hours.