Pure ethanol, the type of alcohol in every beer, wine, and spirit, boils at 78.37 °C (173.1 °F) at standard sea-level atmospheric pressure. That is roughly 22 degrees Celsius below the boiling point of water. But if you are asking because you want to know when alcohol leaves a sauce, how a still separates whiskey from wash, or whether altitude changes anything, the single number only gets you so far. The behavior of alcohol in the real world, where it is almost always mixed with water, is more interesting and more counterintuitive than the textbook figure suggests.
Pure Ethanol Versus the Alcohol in Your Glass
The 78.37 °C figure applies to pure ethanol sitting alone in a flask. Nobody drinks pure ethanol. Beer is roughly 4–6 percent alcohol by volume, wine around 12–15 percent, and even a cask-strength bourbon rarely exceeds 65 percent. The moment ethanol shares a container with water, the two liquids interact, and the boiling behavior shifts. A 12 percent wine does not start losing ethanol at 78 °C and then lose water at 100 °C in two neat stages. Instead, both substances evaporate together across a range of temperatures, with ethanol leaving somewhat faster because it is more volatile. This is why you cannot simply boil a pot of wine and expect the alcohol to vanish while all the water stays behind.
The Azeotrope Problem
If you try to distill an ethanol-water mixture, you eventually hit a wall. At roughly 95.6 percent ethanol by weight, the mixture forms what chemists call an azeotrope: a combination that boils at a single fixed temperature, about 78.1 °C, and produces vapor with exactly the same composition as the liquid. At that point, no amount of ordinary distillation can push the ethanol concentration any higher. The vapor and liquid are identical twins, and boiling just recycles them. This is why grain alcohol sold commercially tops out near 95 percent (190 proof) unless special techniques are used. The azeotrope is a minimum-boiling one, meaning the mixture actually boils at a slightly lower temperature than pure ethanol does.
Getting past the azeotrope requires tricks that go beyond simple heating. One industrial approach uses molecular sieves, tiny porous materials that selectively trap water molecules while letting ethanol pass through. Research comparing different sieve types found that type 3A molecular sieves performed best at separating ethanol from water in these near-azeotropic mixtures.1Chemical Engineering Research and Design. Separation of Ethanol–Water Mixtures Using Molecular Sieves and Biobased Adsorbents Another strategy involves adding a third substance, called an entrainer, that disrupts the azeotrope and lets further distillation proceed. Ionic liquids and deep eutectic solvents can shift or completely eliminate the azeotropic point at concentrations as low as about 5.5 percent by weight, allowing full separation of ethanol and water that ordinary distillation cannot achieve.2Fluid Phase Equilibria. Separation of the ethanol/water azeotropic mixture using ionic liquids and deep eutectic solvents These methods matter for fuel-grade ethanol production, where even a few percent water makes the product unusable as a gasoline additive.
Does Cooking Really “Burn Off” the Alcohol?
One of the most persistent kitchen myths is that alcohol completely evaporates during cooking. Because ethanol boils well below water, the reasoning goes, it should all be gone long before a stew finishes simmering. In practice, a significant fraction sticks around. Researchers who measured ethanol in meat stocks prepared with wine and beer found that the decline in alcohol follows a power-law relationship with the remaining liquid volume: as the dish reduces, the alcohol concentration drops, but it does not drop to zero quickly. The rate of decline turned out to be independent of pot size and cooking temperature, meaning you cannot simply crank the heat to speed up alcohol removal.3PubMed. Fate of ethanol during cooking of liquid foods prepared with alcoholic beverages: Theory and experimental studies
How much stays behind depends heavily on the cooking method. A study that measured ethanol in finished dishes found that fish stew cooked for 45 minutes in a covered pan, with wine added to cold ingredients, retained about 30 percent of its original alcohol. By contrast, beef and rabbit dishes where red wine was added to already-boiling ingredients and then simmered for an hour in a covered pan kept only about 5 percent.4Food Chemistry. Headspace SPME–GC/MS evaluation of ethanol retention in cooked meals containing alcoholic drinks Adding the alcohol to a hot pan and cooking uncovered allows more to escape. Adding it to cold ingredients and sealing the pot traps more vapor inside, which condenses and drips back into the food.
The practical upshot: if you are cooking for someone avoiding alcohol entirely, such as a child, a person in recovery, or someone taking a medication that interacts with ethanol, you cannot assume the dish is alcohol-free just because it spent time on the stove. A flambe, which looks dramatic but exposes the liquid to heat for only seconds, removes very little alcohol. A slow braise reduces the amount considerably but does not eliminate it.
How Distillers Use Boiling Points to Shape Spirits
Distillation is essentially a controlled exercise in exploiting different boiling points. A fermented liquid, whether it started as grain mash, fruit juice, or sugarcane, contains ethanol, water, and hundreds of other volatile compounds, each with its own boiling temperature. Methanol, for instance, boils at about 64.7 °C (148.5 °F), well below ethanol. Various esters, aldehydes, and fusel alcohols have boiling points scattered above and below ethanol’s range. A distiller’s job is to capture the compounds that taste good and reject those that taste bad or are outright harmful.
This is done through “cuts.” The first liquid to come off the still, called the foreshots or heads, is rich in methanol and acetaldehyde. Distillers discard this fraction. The middle fraction, or hearts, is mostly ethanol with the desirable flavor compounds. The tail end, called the tails or feints, carries heavier fusel alcohols with oily, sometimes unpleasant flavors. Where exactly a distiller makes each cut determines the character of the finished spirit. The entire process hinges on understanding the boiling points and volatility of these components and controlling temperature and pressure carefully enough to separate them.5ScienceDirect. Application of distillation in alcoholic beverage production
This is also why homemade distillation can be dangerous beyond the obvious legal issues. Without precise temperature control and a good understanding of the cut points, a person can inadvertently concentrate methanol, which is toxic even in small amounts, into the finished product. Commercial distillers have instruments, experience, and regulatory oversight to avoid this. A backyard operation with a jury-rigged still usually does not.
What Happens at High Altitude
Boiling point is not a fixed property of a substance; it depends on the surrounding air pressure. At sea level, atmospheric pressure is about 101.3 kPa (14.7 psi), and ethanol boils at 78.37 °C. Move to a city like Denver, where the pressure is around 83 kPa, and the boiling point drops by a few degrees. Move to La Paz, Bolivia, at roughly 65 kPa, and it drops further still. The same physics that makes water boil at lower temperatures in the mountains applies to ethanol.
For most everyday purposes, the shift is modest enough to ignore. Your wine sauce in a Denver kitchen will behave almost identically to one made in Miami. But in industrial settings, pressure manipulation is a serious tool. Vacuum distillation deliberately reduces the pressure inside a still so that ethanol boils at temperatures far below its normal boiling point, sometimes as low as 30–35 °C. Breweries use this technique to produce alcohol-free beer: they gently strip the ethanol out of finished beer at such low temperatures that the delicate hop and malt flavors survive largely intact, rather than being cooked away in a full-temperature distillation.
The general principle is straightforward: lower pressure means a lower boiling point. This applies not just to ethanol but to every liquid, and it is why the relationship between pressure and boiling temperature is one of the most useful levers in food science and chemical engineering alike.
Other Alcohols and Their Boiling Points
When people say “alcohol” they almost always mean ethanol, but the alcohol family is large, and the boiling points span a wide range. Methanol, the simplest alcohol with just one carbon atom, boils at 64.7 °C (148.5 °F). Isopropanol, the main ingredient in rubbing alcohol, boils at 82.6 °C (180.7 °F). Butanol, which has four carbons, boils at about 117 °C (243 °F). The pattern is roughly that heavier, longer-chain alcohols have higher boiling points, because larger molecules cling to each other more strongly in the liquid state.
This matters in a few practical contexts. In hand sanitizer, the relatively low boiling point of ethanol or isopropanol is what makes the product evaporate quickly from your skin. In fuel blending, methanol and ethanol have different evaporative behaviors that affect engine performance and emissions. And in toxicology, knowing that methanol boils lower than ethanol explains why it shows up first in a distillation run, which is exactly why the foreshots fraction in spirit production is discarded.
Flammability and Flash Point
Boiling point and flash point are related but different. The flash point of a liquid is the lowest temperature at which it gives off enough vapor to ignite briefly when exposed to a spark or flame. For ethanol, the flash point is about 16.6 °C (61.9 °F), which is dramatically lower than its boiling point. This means ethanol vapor can catch fire at room temperature. You do not need to boil alcohol to create a fire hazard; you just need it to be warm enough to generate vapor, which at typical indoor temperatures it already is.
This is why a flambe works at all. When you heat brandy in a pan and touch a flame to it, the ethanol vapor above the liquid ignites, not the liquid itself. It is also why spilling high-proof spirits near an open flame in a kitchen is genuinely risky. The flash point of ethanol-water mixtures rises as the alcohol concentration drops, which is why you cannot set a glass of beer on fire but you can ignite 151-proof rum without much effort.
For home cooks, the practical lesson is simple: if you are adding spirits to a hot pan, remove the pan from the heat source first, add the alcohol, and then return it to the flame or use a long lighter to ignite deliberately. Pouring from a bottle into a pan that is sitting over a burner creates a vapor trail that can flash back to the bottle.
Inhaled Alcohol Vapor
Because ethanol evaporates readily, especially when heated, anyone working around boiling or simmering alcoholic liquids is breathing in some ethanol vapor. In most kitchen situations, the amounts are trivial. But in industrial contexts, or in the trend of “vaporized alcohol” consumed recreationally, the route of exposure matters. Inhaled ethanol bypasses the digestive system and reaches the brain through the arterial circulation much faster than swallowed alcohol does. A review of the pharmacology of inhaled alcohol noted that this rapid delivery to the brain, skipping the body’s normal first-pass metabolism in the liver, may increase the risk of addiction-related effects compared with drinking the same amount.6PubMed Central. Inhalation of Alcohol Vapor: Measurement and Implications
Distillery workers, who spend hours in enclosed spaces where ethanol vapor concentrations can be substantial, face occupational exposure limits set by health agencies. The U.S. Occupational Safety and Health Administration sets a permissible exposure limit of 1,000 ppm for ethanol vapor over an eight-hour shift. That sounds like a lot, but in a poorly ventilated still house during an active run, concentrations can approach or exceed it. Adequate ventilation is not just about comfort; it is a regulatory and health requirement.
Why Ethanol’s Boiling Point Is Lower Than Water’s
Water molecules form strong hydrogen bonds with each other, creating a network that takes substantial energy to break apart. Ethanol molecules also hydrogen-bond, but less extensively. Each water molecule can form up to four hydrogen bonds with its neighbors, while ethanol’s longer carbon chain gets in the way of building such a dense network. The result is that ethanol molecules escape into the gas phase more easily, which translates to a lower boiling point. This same property is why ethanol evaporates faster than water when you spill it on a countertop, and why an open bottle of wine left out overnight loses some of its alcohol content even without heating.
The difference in volatility between ethanol and water is the entire foundation of distillation, alcohol retention in cooking, and the azeotrope phenomenon described earlier. Without that 22-degree gap in boiling points, none of those processes would work the way they do. At the same time, the gap is small enough that the two liquids co-evaporate readily, which is why separating them completely is harder than it sounds and why the azeotrope at around 95.6 percent ethanol becomes such a stubborn barrier for industrial chemists.7Journal of Chemical Technology & Biotechnology. Effective separation of ethanol–water azeotrope using acetate‐based ionic liquids: from COSMO‐RS screening to process simulation