I don't understand how open fermentation retains any alcohol.

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    "I don't understand" is almost never a good question. It's hard to address an open-ended "I don't". What do you understand/believe to be true, and what don't you? Said another way: Why do you think an open fermentation would not retain any alcohol? – jsled Jul 2 '15 at 21:36
  • aka, how does open fermentation beer retain alcohol without it evaporating? – Greg Jul 2 '15 at 22:10
  • "I don't understand..." was my description to the question since the field was required for submission. Perhaps instead of being a prick with your question sentence structure you should just ask for clarification of the question alone? I don't mean to offend but I feel obligated to inform you of how your input comes across as extremely negative. – Greg Jul 7 '15 at 3:14

Ethanol boils at 78.4C water boils at 100C, impurities in solution increase further the boiling point of these solutions. Unless you are heating the solution to >50C the rate of evaporation will be negligible. The strong surface tension of water also limits the evaporation from solutions.

Also, you have to think of the surface area to volume ratio of an open fermentation, mostly there will be a relatively low SA/vol ratio, unlike a puddle which will evaporate quickly as the SA is high in relation to the volume.

Think of how quickly the water in your bath at home would evaporate with only a few inches of water in, unless you were in a heat wave it would likely take a good few days/weeks for it to evaporate away.

Even in a Belgium style cool ship they are generally 18-24in /45-60 cm deep, and kept at a low temperature <20C. The original idea was to allow hot wort to cool quickly in the shallow vessel and they stop the metabolism of the yeast increasing the temperature of the wort/beer too much by allowing convection and low amounts of evaporation to carry away the heat.

Another thing with open fermenters is that they lower the pressure on the liquid compared to a closed fermenter, this helps to reduce the stress on the yeast and leads to different flavour profiles from the same combination of yeast and wort.

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    Even boiling an alcoholic drink does not always burn away all the alcohol (unless you boil away all the liquid). – Atron Seige Jul 6 '15 at 14:14
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    Great response, I didn't realize that the surface area to volume ratio could affect the in-solution alcohol retention so well! I suppose I always just assumed that any alcohol in any solution evaporated at a rate the same as pure alcohol which you indirectly explained is not the case. – Greg Jul 7 '15 at 3:17

Alcohol doesn't evaporate that quickly. We might as well ask how the water stays in the beer too.

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  • Understood, however I was unintentionally comparing a liquid like water to a liquid such as pure alcohol. If these were set side by side obviously the alcohol would evaporate at a much higher rate than the water. I didn't realize that one liquid in-solution of the other could affect the evaporation rate of the alcohol. Thanks for your input! – Greg Jul 7 '15 at 3:20

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