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Alcohol Drinks

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Genielle | 12:19 Mon 29th Nov 2004 | Food & Drink
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How do you calculate the alcohol percentage on a home made rum punch? 
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Do't take this a sgospel, as I've never done it. If you take a quantity of your punch and measure the volume, then heat it so the alcohol boils off (about 65-70C I think), maintaining at this temperature until liquid stops disappearing, then re-measure the volume. This will show what %age was ethanol. eg if you had 100ml at the start, and 70ml at the end you lost 30ml, so the brandy was 30% alcohol v/v. This would however require proper distillation equipment, and acurate measuring recepticles.

If you put in a whole 1 litre bottle of 40% abv rum (alcohol by vloume) and dilute it with three litres of juice / cola / lemonade etc, there will now be;

40/100 x 1000 ml of alcohol (ie 40% of 1 litre) = 400 ml in 4000ml of liquid (the total amount of liquid).

So the new abv would be 400 / 4000 x 100 = 10% abv

Ignore the distillation method, I'm afraid.

Ethanol forms an azeotropic mixture with water, which means that you can't distill pure ethanol from an ethanol and water mixture - you will always have some water distilled off.

...in that case you'd have to add magnesium sulphate then filter it off, this will remove the water.
Of course you could use gas chromatography to calculate the exact % alcohol.
So are you saying a fractional distilation tower is no good for this process?
I am of the opinion that gas chromatography will give a more accurate measurement of % alcohol than fractional distillation, as trilobite says: it is an azeotrope. They agree with me http://www.ritchieproducts.co.uk/calculatingABV.htm

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