Does Heating Really Burn Off All the Alcohol in Cooking?
― After an Hour of Simmering, About a Quarter Is Still There
"Alcohol boils at 78°C, so it flies off as soon as you heat it." That's the usual kitchen explanation. But when people actually measure it, alcohol is surprisingly slow to leave the pot. Alcohol mixed with water can only escape a little at a time, along with the water.
It's a chilly weekend, and you're simmering a beef stew with plenty of red wine. For the meat-and-potato dish, you add sake and mirin. A soft smell of alcohol drifts through the kitchen.
Someone asks, "The kids will eat this too. Is it OK?" You might answer, "I cooked it properly, so the alcohol is gone."
But how sure can you be that it's "gone"? In fact, researchers have cooked real dishes and measured this very question.
Only two reasons it won't leave
Alcohol dissolved in water doesn't boil off on its own at 78°C. The mixed liquid boils as a whole, and the steam carries both water and alcohol. Most of the steam is water.
How much alcohol leaves with the steam depends on how concentrated it is in the pot. It drops fast at first, but as it thins out it escapes more sluggishly, and the last bit is hard to get rid of.
Let's go through them in order. First, the results of actual measurements: how much really stays behind?
Measured: about 25% remains after an hour of simmering
Researchers at the US Department of Agriculture cooked many dishes made with alcohol and measured what was left. The table summarising their results is still in use today.
Look at Figure 1. If you add alcohol to a boiling liquid and turn off the heat straight away, about 85% remains. After 15 minutes of simmering, it falls to about 40%. After that, though, the decline slows sharply. About 35% remains at 30 minutes, about 25% at 1 hour, and about 10% even at 2 hours. It took around two and a half hours of simmering to get close to zero.
Why doesn't it all leave at 78°C?
Pure alcohol boils at about 78°C. Water boils at 100°C. So it's tempting to think that "the alcohol boils off first, on its own." But that is true only if the two were separate liquids.
In a dish, the alcohol is fully dissolved in the water. The mixture boils as a whole, at a temperature between 78°C and 100°C. At the strength of wine, it is said to boil at around 90°C. And the steam that rises contains both water and alcohol (Figure 2).
It's true that the alcohol in the steam is several times more concentrated than in the pot. That's why simmering does reduce the alcohol. Even so, most of the steam is still water. To drive out all the alcohol, you have to boil off a lot of water with it. It is hard for "only the alcohol to vanish" while the liquid has barely shrunk.
The thinner it gets, the slower it escapes
The amount of alcohol that leaves with the steam is set by how concentrated it is in the pot at that moment. While it's strong, the steam carries plenty of alcohol. Once it's thin, the same amount of steam carries away only a little.
So the decline goes "fast at first, then slower and slower." That is why the line in Figure 1 drops steeply at the start and then flattens out. Getting rid of the last 10% can take more than an hour.
The shape of the pot matters too. With a lid on, steam falls back into the pot, so more alcohol is said to stay. A wide, shallow pan lets more steam out, so the alcohol drops faster. In baked goods cooked in an oven, the centre doesn't get very hot, so nearly half is said to remain even after about 25 minutes of baking.
Setting alcohol alight for a flambé looks as if it would burn the alcohol away. But the flames last only a few seconds to a dozen or so, and what burns is just the alcohol in the vapour rising from the surface. Measurements suggest about 75% stays in the dish. The point of a flambé is to add aroma, not to remove alcohol.
So how should we think about it?
The alcohol in ordinary cooking is not much per serving. As the calculation below shows, even in a wine stew, the alcohol left in one portion is about a twelfth of a can of beer. For most people, that is not an amount worth worrying about.
But "cooked" does not mean "zero." For small children, pregnant women, people told to avoid alcohol, and people trying to quit drinking, whether it is zero or not can matter. When serving these people, it is safer to make the dish without alcohol. The best precaution is not to assume that "I boiled it off, so it's fine."
Summary
Alcohol dissolved in water cannot boil off on its own at 78°C. It leaves a little at a time, mixed into the steam with the water. And the thinner it gets, the more sluggishly it leaves, so about a quarter remains after an hour of simmering and about three quarters after a flambé.
Alcohol can only leave the pot by hitching a ride on the steam.
That's why it doesn't vanish quickly, however you boil or bake.
Another kitchen tale about boiling is tested in Does adding salt to water make it boil faster? For the fermentation that produces the alcohol in cooking wine, see What's the difference between fermentation and rotting? For the alcohol that forms inside bread dough, head to Why does bread rise?
- Put about 3 tablespoons of sake or mirin in a small pot, add 3 tablespoons of water, and heat. Once it boils, turn off the heat after 30 seconds.
- When it has cooled, put a little on a small plate and smell it. You should still clearly smell the alcohol.
- Prepare the same thing again, and this time simmer it over low heat for about 10 minutes. Compare how much the liquid has shrunk from the starting amount, and how strong the smell is.
Don't lean over the pot near the flame, and always smell it only after turning off the heat and letting it cool. The steam can catch fire, so don't heat it strongly for long. If children are doing this, an adult should handle the heat, and nobody should taste it.
For the curious ― terms, formulas and links to textbooksFrom middle-school science to university courses, with the level of each part marked
- Middle schoolCovered in middle-school science
- High schoolCovered in high-school chemistry
- High school+Advanced high-school material, or textbook sidebars
- UniversityUniversity-level courses not taught in high school (physical chemistry, chemical engineering)
- ResearchNot yet settled textbook knowledge; researchers are still investigating
Middle schoolTerms: this phenomenon has names
- Boiling point: the temperature at which a liquid starts to boil. Water boils at 100°C and alcohol (ethanol) at about 78°C. The boiling point of a mixture lies between the two.
- Distillation: a method of separating components by boiling a liquid and cooling the steam. In middle school it is taught with an experiment that extracts an alcohol-rich liquid from wine. Even in that experiment, the liquid that comes out contains water.
- Retention: the share of an ingredient added before cooking that is still there in the finished dish. In this article, it means what percentage of the added alcohol remained.
Middle schoolHigh schoolCheck with a formula: how many grams of alcohol remain in one portion of wine stew?
Consider a stew for four people, made with 200 millilitres of red wine and simmered for 1 hour. The symbols mean: A is the amount of alcohol added, R is the retention (it changes with time), and Aleft is the amount remaining.
| In symbols | Aleft = A × R(t), A = V × c |
| In words | Alcohol left = (amount of liquor × alcohol strength) × retention set by simmering time |
| Where it comes from | Alcohol doesn't disappear; it only decreases by the amount that leaves the pot as steam (conservation of matter). Retention falls slowly over time because the rate at which alcohol leaves with the steam depends on its concentration in the pot, and its values are set by measurement |
| Amount of liquor V (red wine) | 200 mL |
| Alcohol strength c | 12% (0.12) |
| Retention R after 1 hour of simmering | about 25% (0.25) |
| Weight of 1 millilitre of alcohol | about 0.79 g |
| One can of beer (350 mL, 5%) | about 14 g of alcohol |
| Alcohol added | 200 × 0.12 = 24 mL |
| Amount left after 1 hour | 24 × 0.25 = 6 mL |
| Convert to weight | 6 × 0.79 ≒ 4.7 g |
| Divide among 4 people | 4.7 ÷ 4 ≒ 1.2 g |
| Compare with one can of beer | 14 ÷ 1.2 ≒ 12 |
The alcohol left in one portion is about 1.2 grams, roughly a twelfth of a can of beer. That's small, but not zero. If the same dish were simmered with a lid on, or for only 15 minutes, retention would be about 40%, and the amount left would rise by about 1.6 times.
High schoolHigh school+How does a mixture boil?
High schoolIn high-school chemistry you learn "fractional distillation" as a way to separate liquids with different boiling points. But components separate cleanly in fractional distillation only because the apparatus cools and re-boils the vapour many times over. Boiling once in a pot leaves the steam as a mixture of water and alcohol.
High school+A diagram that plots the concentration of the liquid against that of the vapour at each temperature is called a "vapour-liquid equilibrium diagram." For water and alcohol, the vapour from a dilute liquid is several times richer in alcohol than the liquid. Even so, each time steam leaves, the pot gets more dilute, and the alcohol carried off falls too. This is what makes the "flat tail" in Figure 1.
UniversityDeviation from Raoult's law, and the Rayleigh distillation equation
In an ideal mixture, the vapour pressure of each component is proportional to its fraction in the liquid (Raoult's law). Mixtures of water and ethanol deviate strongly from this: dilute ethanol has a large "activity coefficient" and escapes more readily than expected. Even so, alcohol remains, because the amount of steam itself is limited. How much of each component is lost as the liquid shrinks in a single boil is given by the "Rayleigh distillation equation," and depends on a quantity called relative volatility. Water and ethanol also form an "azeotrope" at about 96% by mass, beyond which distillation cannot make it any stronger.
📖 Derivations and further reading: Vapour–liquid equilibrium (Wikipedia, in Japanese) ／ Azeotrope (Wikipedia, in Japanese)
ResearchWhat we still don't know well
- Variation between dishes. The retention figures most often quoted are rough guides based on measurements of a limited set of dishes. Pot size, heat, the amount of ingredients and the amount of liquid are said to change the result greatly even at the same time, and there are few measurements from home cooking.
- Alcohol that has soaked into the ingredients. How much harder it is for alcohol soaked into meat and vegetables to escape, compared with alcohol in the broth, has not been well studied.
- Links with fat and sugar. It has been suggested that lots of fat or sugar may change how alcohol leaves. This topic also ties in with research on aroma.
In other words, this article too is "an explanation of what is understood so far." Please treat the retention figures as rough guides that rise and fall with cooking conditions.
Links to textbooks (by level)
| Level | Subject / unit | Where in this article |
|---|---|---|
| Middle school | Science, year 1: "changes of state and boiling point", "distillation" | Alcohol boils at about 78°C, water at 100°C / distilling wine |
| High school | Chemistry: "separation and purification (fractional distillation)" | Why one boil doesn't separate the components |
| High school+ | Advanced chemistry: "vapour-liquid equilibrium" | How concentrated the alcohol in the steam is, and why the decline slows |
| University | Physical chemistry / chemical engineering: "Raoult's law", "Rayleigh distillation equation", "azeotrope" | Why retention falls slowly over time |
| Research | Food science and culinary science | Variation in retention between dishes |
| ― | Links to daily life | Deciding what to do when serving children, pregnant women, or people avoiding alcohol |
- US Department of Agriculture (USDA), Table of Nutrient Retention Factors, Release 6 (2007)
- Augustin, J. et al. "Alcohol retention in food preparation." Journal of the American Dietetic Association, 92(4), 486–488 (1992).
- Wikipedia, "Vapour–liquid equilibrium" (気液平衡, in Japanese)
- Wikipedia, "Azeotrope" (共沸, in Japanese)
- Harold McGee, On Food and Cooking (Japanese edition: Magi Kitchen Science マギー キッチンサイエンス, Kyoritsu Shuppan 共立出版)
* This article is a science explainer for general readers. The figures given are rough guides and estimates to help you understand the mechanism. How much alcohol remains varies greatly with cooking method and conditions. If you are pregnant, or a doctor has told you to avoid alcohol, follow the advice of your doctor or other professional.