Alcohol Drinks

[Genielle]

How do you calculate the alcohol percentage on a home made rum punch? 

[greenday]

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.

[trilobite]

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

[trilobite]

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.

[greenday]

...in that case you'd have to add magnesium sulphate then filter it off, this will remove the water.

[j2buttonsw]

Of course you could use gas chromatography to calculate the exact % alcohol.

[archbishop]

So are you saying a fractional distilation tower is no good for this process?

[j2buttonsw]

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