Wine, beer, brandy and other alcoholic beverages are common ingredients in cooking. As the alcohol is heated, it will gradually evaporate. However, the length of time it takes for most of the alcohol in a dish to evaporate depends on the method of cooking. Alcohol seldom completely "cooks out" of a dish.
The Science of Sauces
Ethyl alcohol, also called ethanol, has a lower boiling point than water. Ethanol begins to evaporate at 172.9 Fahrenheit (78.3 C). As a result, ethanol will begin to evaporate out of a liquid when it is heated to this temperature, even if the rest of the liquid isn't boiling. However, not all of the ethanol will evaporate out of the solution at once, just as all the water in a liquid doesn't boil off immediately when the liquid is heated to 212 F (100 C).
Burning and Boiling
A 2007 study released by the Nutrient Data Laboratory, a U.S. Department of Agriculture facility in Beltsville, Maryland, reveals that different methods of cooking lead to very different levels of alcohol remaining in a dish. In some cases, the results are surprising. Flaming, in which the alcohol in a dish is actually set afire, still leaves about 75 percent of the original alcohol content behind. Stirring alcohol into a mixture and baking or simmering reduces its content significantly. After only 15 minutes, the alcohol will have been reduced to 40 percent of its original level.
It's About Time
The longer food is cooked, the greater the reduction in the alcohol content will take place. However, as the level of alcohol in the food decreases, the rate of reduction also decreases. For example, baking or simmering a dish for 15 minutes will reduce the original alcohol level to 40 percent. Another 15 minutes, however, will only have reduced the alcohol level to 35 percent. After a total of an hour, the alcohol level will still be at 25 percent. Even after two and a half hours, 5 percent of the original alcohol will still remain.
Five Percent Solution
The long cooking times needed to boil off alcohol in cooking essentially mean that the last alcohol will not evaporate until all the liquid it is dissolved in evaporates. This is obviously impractical for almost all recipes. As a result, there will usually be a trace amount of alcohol left in any food cooked with alcohol. Because the quantities of alcohol used in cooking are typically small, this shouldn't trouble people who want to avoid becoming drunk. However, diners who are avoiding alcohol for other reasons -- such as a religious prohibition -- may want to explore alternatives.
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