Perhaps you can shed some light on this topic for me. I've recently researched the topic of boiling off alcohol while cooking--specifically how long one needs to simmer alcohol to boil it off.

I'd come across a couple of sites which showed tables of simmering times and percentage of alcohol remaining. Since I am a math-head, I noticed that something didn't quite jive in the tables I was viewing.

I thought to ask a chemistry expert to see if there is something unusual going on chemically to explain these inconsistent values in the tables.

I don't want to make this a novel, so I will use only a few entries in the tables to illustrate my point.

Simmering time Alcohol remaining

15 minutes 40%

30 minutes 35%

2 hours 10%

So what the table suggests is that if you simmer a solution containing alcohol, after the first 15 minutes, you will have 40% of the original amount of alcohol in the solution. If you simmer for an additional 15 minutes (total of 30 minutes) you will have 35% of the original amount of alcohol left in the solution.

So, (according to the table) if I have a solution which originally contains 100 ml of alcohol in the solution, and I simmer it for 15 minutes, I will have 40 ml of alcohol left in the solution. Then if I simmer it another 15 minutes (30 minutes total), I will have 35 ml of alcohol remaining in the solution.

However, If I start with a solution containing 40 ml of alcohol in the solution (let's say it's the solution from above after the first 15 minutes), and I simmer it for 15 minutes, I will be left with 16 ml of alcohol in the solution (again, according to the table). You can see my dilemma; 16 ml does NOT equal 35 ml. The math doesn't work.

I am wondering about the nature in which they'd come up with these values or the methodology they used in their experiments.

Can you help me to understand what is going on here?

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    $\begingroup$ (Who deletes my comments here?) @Bob: After half an hour of boiling, your sauce is not the same as it was when you started cooking. It wouldn't even work for water, because the numbers depend on the original absolute concentration. Also: Lid or no lid? Heating power? Stirring? Amount of fat in your sauce? Humidity of surrounding air? Those numbers you found in some book are just arbitrary, anecdotal, unscientific nonsense, unless they were accompanied by some lenghty, good explanation, but then you wouldn't be asking here. Being good in math, you suspected sth is wrong here, and you're right $\endgroup$ – Karl May 1 '18 at 15:26
  • $\begingroup$ Thank you for your response Karl. I appreciate your time and efforts. $\endgroup$ – Bob May 1 '18 at 18:07
  • $\begingroup$ Let's say, for the sake of argument, that there is no lid, 50% relative humidity, 25% fat content, 210 square cm surface area, and just enough heat to simmer, starting concentration of 10% alcohol. How would I determine the rate at which the alcohol is evaporating at various times throughout the process? $\endgroup$ – Bob May 1 '18 at 18:11
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    $\begingroup$ By measuring it. :-| $\endgroup$ – Karl May 1 '18 at 20:03

The original source of the data is Alcohol retention in food preparation Journal of the American Dietetic Association vol. 92, April 1992, pages 486-488.

After 2.5 hours of simmering at 85 degrees C, pot roast Milano still retained 4-6% of the original alcohol content.

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    $\begingroup$ ... and orange chicken burgundy contained 0.07% if cooked in a 12" pan, and 0.4% in a 10" pan. A nice example of cargo cult science, at least they didn't suppress that particulary obvious piece of evidence. :-D $\endgroup$ – Karl May 1 '18 at 20:28

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