Is it possible to obtain more concentrated alcohol by using wine in a solar still instead of seawater?

If yes, as I suspected, how does the concentration (of alcohol) of the distillate vary with time? I would expect it to rise to a peak, then fall to the original concentration as the water also get condensed into distillate. Can you give an analysis for this variation?


closed as off-topic by Brandon Enright, Ali, Kyle Kanos, ACuriousMind, Jim Aug 30 '14 at 14:02

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  • $\begingroup$ Yes, one can make absolutely horrible brandy in a solar still. $\endgroup$ – CuriousOne Aug 30 '14 at 4:52
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    $\begingroup$ This question appears to be off-topic because it is about making alcohol and not physics. Maybe chemistry? Or HomeBrew.StackExchange.com? $\endgroup$ – Kyle Kanos Aug 30 '14 at 11:03
  • $\begingroup$ @KyleKanos I'm not trying to make alcohol obviously... If I were, I wouldn't be using a solar still. I just happen to be interested in solutions of alcohol and water. Even if I were interested only in that, the question is related absolutely to intermolecular forces, condensation, and evaporation. What I'm asking for is a treatment as in physics, not how a sommelier would analyze it or something. I hope I could persuade people to stop interpreting my question this way. $\endgroup$ – resgh Aug 30 '14 at 13:02
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    $\begingroup$ @namehere: even if your goal isn't about making alcohol, this is more of a chemistry question than physics. $\endgroup$ – Kyle Kanos Aug 30 '14 at 13:37
  • $\begingroup$ I agree that Chemistry would be better. $\endgroup$ – Danu Aug 30 '14 at 14:02

Have a look at the following phase diagram:

Phase diagram

(Diagram from this web site)

I've drawn the vertical green line to mark 15% ethanol by mass, which is about the maximum you can expect from wine. The boiling point of the mixture is the point where the green line crosses the blue line so it's about 90ºC (the diagram is approximate, so don't read it too literally). The composition of the vapour is given by the pink line, so follow the horizontal green line over until it hits the pink line, and we see the vapour is about 40% by mass of ethanol.

So when you first start distilling your wine you'll end up with a distillate that's about 40% ethanol. To get the ethanol more concentrated you would have to take the distillate, put it back into the still and distill it again.

If you leave the wine in the still the ethanol content in the liquid will fall as ethanol is removed. Consequently the boiling point will rise and the ethanol content of the distillate will progressively fall. For any water/ethanol proportion you can read off the boiling point and distillate composition from the phase diagram.

For anyone willing to read past the tl;dr limit, note that the blue line reaches a minimum value at 95.6% ethanol. This is known as the eutectic point. At this point the composition of the vapour and the liquid are identical, so you cannot concentrate the ethanol any further by repeated distillation. To get the ethanol any more concentrated you have to add a third component to shift the eutectic point. This process is called azeotropic distillation and in the ethanol/water system benzene is used.

  • $\begingroup$ What vertical green line? $\endgroup$ – resgh Aug 30 '14 at 10:33
  • $\begingroup$ @namehere: the line that passes through the letter u of the word liquid. $\endgroup$ – John Rennie Aug 30 '14 at 10:57

There's no reason why it wouldn't work. In fact, since most fermenting yeast is limited to ~15% or so ethanol by volume, evaporative (or other) distillation is needed to produce stronger drinks. All that's required is basically that the two substances (water and ethanol in this case) have different volatilities. In this case, you'd collect ethanol and leave behind water, rather than collect water and leave behind salt.

Note that even the best evaporative distiller you can make (probably with heating and cooling mechanisms) is limited to less than 96% ethanol output. But that's 191 proof (US) or 167 degrees proof (UK) - pretty strong stuff.

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    $\begingroup$ How does the concentration (of alcohol) of the distillate vary with time? I would expect it to rise to a peak, then fall to the original concentration as the water also get condensed into distillate. Can you give an approximation for this variation? $\endgroup$ – resgh Aug 30 '14 at 5:10
  • $\begingroup$ @namehere that's a good question I would hope an actual chemist or chemical engineer would calculate for me, but I'll think about it... $\endgroup$ – user10851 Aug 30 '14 at 5:23

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