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Determination and adjustment of the alcohol content

Whisky is bottled with the most diverse alcohol contents. The legal minimum amount is presently at 40%. For alcoholic beverages these percentages usually account for the portion of the volume of the liquid (ABV - absolute by volume). One could also take percentages of the weight, but over the past we got accustomed to percents by volume.

Did you see a cowboy in a western movie drink half a bottle of whisky in the saloon? Afterwards he straightly went out and dueled successfully? That was possible. In the wild west light-whisky was sold with only 15 to 25%. The wilder the saloon, the less alcohol was in the bottle. Everybody diluted a little more and in the end, the whisky was hardly stronger than a good wine.

In more recent times whisky was also bottled with smaller alcohol contents. However they are called differently. The Irish Marlfield from 1946 with only 20% is therefore called 'Whisky Liqueur'.

So how do you determine the alcohol strength of a whisky? - with the help of a spindle. In each spirit safe of the Scottish distilleries are spindles and thermometers. A spindle is a swimming body, which measures the density of a liquid. Since the density is dependent on the temperature, you have to correct the density value in a table considering the measured temperature. Thus the alcohol content can be determined accurately.

But what did they do 200 years ago in Scotland?

Well, they used the resources available. The cask strength whisky was mixed with gun powder and the mmixture was ignited. If the mixture burned down briskly with a bright flame, the whisky had a 'Proof' alcohol content. - it was certificated!

If the mixture however burned down only weakly, the alcohol was 'Under Proof'. And if the mixture almost exploded, the alcohol content was 'Over Proof'. Even today this procedure in the description is still visible e.g. Aberlour 100 Proof, or Glenfarclas 105 Proof.

With the help of the spindles the alcohol strength can be determined far more exactly. 100 Proof in Scotland correspond to a alcohol content of approximately 57 ABV% (absolute by volume). Each increase of around 5 Proof corresponds to an alcohol strength increase of 3%. To make it a bit more complicated the Americans defined 100 Proof differently. For them 100 Proof it is only 50 ABV%. In the USA you can get the alcohol content by simply dividing the proof number by 2. Whether this is due to the American Pragmatism or whether the gun powder in the wild west possessed more explosive yield? Who really knows that accurately?

Today Whiskey and especially Scottish Whisky are bottled in the following strengths:

¹⁾ These Numbers are not completely accurate

As correct Central Europeans we adhere in the following to the metric system with its percentages by volume.

Reduction of the drinking strength

If you want to dilute whisky with water, what ratio between water and whisky do you have to select, in order to receive a certain alcohol strength? If you mix 1:1 it is simple. The alcohol content reduces to the half. Is there a simple formula, with which you can determine the alcohol content of any mixing proportion? And is there a formula with the help of which the quantity of water can be determined, in order to reduce a whisky of a given strength to a smaller one?

There are two ways to calculate the alcohol content:

1. Over the absolute alcohol content

2. With the help of the mixture cross

1. Determination of the percentage over the absolute alcohol content

Problem:
A glass is filled with 4cl whisky with 46%. How high is the alcohol content, if I add 2cl water? The mixing ratio whisky:water is 2:1.

Result:
The absolute alcohol quantity in the glass is:
4cl * 46% = 0.04 liters * 0.46 = 0.0184 liters

After addition of 2cl water the total liquid volume increased to 6cl. You get the alcohol strength, by setting the absolute alcohol volume in relation to the total liquid volume:
0.0184 litres/0.06 litres = 0.3067 = 30,67%

In the following table you find the results of this calculation for the usual whisky strengths.

2. Determination of the percentage using the mixture cross

Problem:
A glass is filled with 4cl whisky with 57%. How much cl water do you have to add to the whisky, in order to receive an alcohol content of 40%?

Result:
The calculation takes place with the help of the mixture cross. The mixture cross is a simple graphic aid, to accomplish the calculation.

The mixture cross contains five fields. An unknown field may be calculated by the other two on the diagonal. There are the two following equations:

If fields on the right side are missing, the equations can be converted to the following:

But enough of the theory. - Here is the answer to the problem:

You have to add 1,7cl of water (57-40=17) in order to receive a whisky with 40%. The total volume of whisky with 40% is 5,7cl.

The mixture cross can not only be used for the mixture of water and whisky, but also percentages of mixtures of whiskies with different strengths may be calculated.

This applies not only to the quantities used here, but also to multiples and fractions of this.