Alcohol, typically referring to ethanol found in beverages, can certainly be boiled. Boiling is the process where heating causes a phase change, transforming the liquid into a gas. The common misunderstanding is that alcohol instantly vanishes when heated, which overlooks the physical chemistry involved.
The Chemistry of Alcohol Vaporization
Boiling occurs when a liquid changes into a vapor as its vapor pressure equals the surrounding atmospheric pressure. Ethanol has a significantly lower boiling point than water, which is often mixed with it in solutions. Pure ethanol boils at approximately 173°F (78°C), while water requires 212°F (100°C) at standard atmospheric pressure.
The difference in boiling temperature is explained by the molecular forces holding the liquids together. Water molecules form strong connections through hydrogen bonding, which requires a large amount of energy to break, resulting in a high boiling point.
Ethanol also forms hydrogen bonds, but its molecular structure includes a hydrocarbon chain that interferes with the strength of these bonds. The attractive forces between ethanol molecules are consequently weaker than those between water molecules. Less energy and a lower temperature are needed to convert liquid ethanol into a gas. When heating an alcohol-water mixture, such as wine or spirits, the ethanol vaporizes before the water begins to boil.
Alcohol Retention in Cooked Foods
Although ethanol has a lower boiling point, it does not quickly evaporate completely during cooking. When alcohol is added to a dish, it mixes with water and other ingredients, making the evaporation rate highly variable. Retention is influenced by cooking time, heat intensity, and the surface area of the cooking vessel.
A long cooking duration is the most effective way to minimize alcohol content. For example, a dish simmered or baked for 15 minutes can still retain approximately 40% of the alcohol added. Extending the cooking time to one hour reduces the retention to about 25%.
Even after prolonged simmering, a small amount of alcohol remains in the food; after two and a half hours of cooking, retention is still around 5%. Other cooking methods show varied retention rates; for instance, alcohol added to a boiling liquid and immediately removed from heat can retain 85%. Baking is generally less effective than long simmering in a wide, uncovered pan, where a larger surface area allows more vapor to escape.
Handling Alcohol Safely During Heating
Heating alcohol, especially to its boiling point, introduces safety considerations due to the flammability of the vapor. Ethanol vapor is highly flammable and readily ignites upon contact with an ignition source, such as an open flame or electrical spark. Pure ethanol has a flash point—the lowest temperature at which its vapors will ignite—of about 57°F (14°C).
Adding alcohol to a hot pan, a technique used in flambéing, is hazardous because the liquid instantly vaporizes and the resulting fumes can easily catch fire. Since these vapors are denser than air, they can travel along a surface to a distant ignition source and flash back to the container. Therefore, alcohol should be kept away from any heat source other than the one used for cooking.
When boiling large quantities of alcohol, such as during extraction or distillation, proper ventilation is necessary. Concentrated ethanol vapors can cause irritation to the eyes and respiratory tract, and inhalation of high concentrations can lead to dizziness or drowsiness. Working in a well-ventilated area or under a fume hood helps disperse the vapors and mitigate the risk of inhalation and fire hazards.