Measurement of Alcohol

Hydrometer

Do you want proof?
I recently read an article published by one of the daily newspapers about very alcoholic cocktails and it contained so many errors, it was clear the author had no idea about how alcohol is measured. Not that there’s any shame in being confused by all the different terms and units of measurement – it can get quite tricky so I thought I’d help to clarify some of the facts about alcohol measurement (Although I probably wouldn’t write any newspaper articles on the subject until I DID know the difference)
First things first – even the term ‘alcohol’ is misleading. What we generally refer to in the booze world is specifically ethanol. Ethanol is a type of alcohol which our bodies are able to safely metabolise when drunk in moderation and produces the familiar feelings of euphoria and giddiness. There are other types of alcohols which we cannot process and can lead to serious injury and death when consumed. It is ethanol which is the ‘alcohol’ in beer, wine, vodka, Whisky and blue WKD.
Ethanol is very neutral. In its purest form, it is odourless, colourless and has practically no flavour. When we are talking about measuring alcohol during distilling we are usually referring to the percentage of purity of the ethanol. e.g. If we say a Whisky has been distilled to 72% that means there will still be 28% of impurities (flavour compounds called congeners) and you will still have some flavour of the base ingredient. When you make vodka, you are looking at an ethanol purity of at least 96% which is why even if they were both made from the same ingredient (e.g. barley), the vodka will not taste like the grain in the same way that Whisky does.
Under European law, which we adopted in Britain in 1980, we retail alcoholic products according to how much pure ethanol is in the liquid as a percentage of its total volume (ABV = Alcohol By Volume) so in a bottle of Whisky at 40%abv, 40% of the liquid is ethanol and the other 60% is mainly water and some dissolved flavouring matter. In a bottle of wine, you may find that it is 14%abv and the other 86% could be water, sugars, preservatives and other flavouring matter.
Recently there has been a lot more emphasis on the effect of alcohol with regards to general health and the World Health Authority have placed guideline limits on the recommended consumption of alcohol for men and women. This is measured in ‘units’ so you can supposedly accurately gauge your intake regardless of how it is being consumed (beer, wines, spirits etc). In Europe, one unit is equal to 10ml of pure ethanol which works out to be a 25ml measure of spirit at 40%abv, a half pint of beer at 3.4% or a small glass (125ml) of 9%abv wine. This is where it gets a bit confusing because a lot of beers are ‘export strength’ and wine is generally stronger nowadays so few people are able to know exactly how many units they are consuming and find that they regularly exceed the guideline amounts (2 per day for women 3 for men and no more than 21 (women) and 28 (men) in a week)
The Americans often use a system where the ‘proof’ is double the abv of the spirit – this is commonly seen in 151 proof rums (75.5%abv) and Wild Turkey 101 (50.5%abv) and is not to be confused with the old British proof system when we used to use the Sikes scale of proof. This laid down proof as being 57.15%abv – the concentration of alcohol needed in a liquid to allow gunpowder to still ignite. It is thought that it could be ‘proved’ that the alcohol was strong enough for taxation purposes in the 16th century by the revenue collectors adding a pellet of gunpowder and lighting it. This also became crucial on board ships where lots of rum was being transported for the ratings’ daily ration because if a barrel sprung a leak on board, it wouldn’t endanger the powder if it was over-proof.
According to the Sikes scale then, 57.15 was 100 degrees proof and therefore 100% pure ethanol would be 175 degrees. Whisky was most commonly bottled at 70 degrees (40%abv) – The Canadians still largely employ this method of displaying alcohol content.
So yes, proof, degrees, units, percent and the like can make the whole business of measuring alcohol quite tricky to the uninitiated but once you have the hang of it, you will clearly see that a drink containing a shot of vodka at 40%, a shot of gin at 40% and a shot of rum at 40% is still only 40%abv and NOT 120% alcohol!
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3 thoughts on “Measurement of Alcohol”

  1. Was discussing this only the other day with someone (from within rich’s company). Particularly the proof system and its history. Good to understand the fundamentals of what we pour

    Liked by 1 person

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