Alcohol content, Alcohol by Volume & Proof
Words by Simon Difford
"You are what you eat" and this extends to what you drink - more than mere calories and nutrients. Unlike most foods, what you drink may also well contain ethanol alcohol - calorific in itself. Like calories, consumption of too much alcohol has health consequences. So how many calories and how much alcohol does each drink have? And how do stated "units of alcohol" and "standard drinks" compare?
At a vodka distillery, I was once given a glass of neutral spirit that had been "diluted back to bottling strength" to sample. As soon as it hit my mouth, I realised it was undiluted and 96% alc./vol. rather than the 40% bottling strength I was told to anticipate. Stood in an office without an obvious place to spit, I stupidly swallowed the mouth-burning spirit. That rogue sample and the resulting burn to my insides was a reminder of the importance of knowing the strength/alcohol content of what you're drinking.
Alcohol content of cocktails on Difford's Guide
We've long recorded calorific values for ingredients used in cocktail recipes on Difford's Guide so we can calculate and state how calorific (in kcals) each cocktail recipe is. We also record the alcohol strength of each ingredient and use this to calculate the total alcohol strength of each cocktail.
Calculating the alcohol strength of a cocktail is not as straightforward as calorific value due to the amount of dilution imparted from melting ice varying according to the mixing method used (shake, stir, blend, etc.).
Obviously, the size of the ice cubes and how cold that ice is will also affect the amount of dilution the ice imparts, and so the cocktail's alcohol strength. For our calculations, we assume large 25mm (1 inch) cubes of ice from an ice machine and used from a bar's ice well. Hence, if using ice straight from a domestic freezer then perhaps consider leaving it to temper at room temperature for a short period before use.
Our clever coding (thanks Matt) allows for dilution from ice and even calculates alcohol contributed by dashes and drops of bitters. However, due to variables we can't control or allow for, the alcohol strength and volumes we give for each cocktail are approximate values.
Alcohol by Volume & Proof
Abbreviated as 'alc./vol.' and also commonly just 'abv', alcohol by volume is a measure of a liquid's alcohol strength, recorded as a percentage of alcohol by volume at a given temperature (15°C). Alcohol by volume, the most commonly used method of recording alcoholic strength across the world is more properly known as the 'Gay Lussac Scale', named after its originator, a French physicist.
At one end of the Gay Lussac Scale, zero alcohol (water) is equal to 0% alc./vol., while at the opposite end, pure alcohol (proof) is measured at 100% alc./vol.
In the USA, alcohol strength is often stated in "proof", proof being twice the percentage of alc./vol. (double the percentage of alcohol contained in a solution at 60°F or 15.6°C). Hence 50% alc./vol. equates to a 100° proof spirit.
Pure Alcohol equals:
100% Gay Lussac alcohol by volume (alc./vol.)
200° US Proof
While on the subject of alcohol strength, I should add that I've explained "overproof" and "Navy strength" on another page as each has an interesting back story.
Grams of pure alcohol
We also state grams of pure alcohol in each cocktail on Difford's Guide – the mass of pure alcohol calculated by multiplying the volume of serve by alc. /vol. by volumetric mass density.
Standard drink & Units in a drink
Expressing alcohol in a drink as a number of "standard drinks" or "units" is used by governments around the world to help their populations judge and keep track of how much alcohol they are drinking. However, depending on what country you are in, it's not only the term used that varies (standard drink or unit) but the amount of alcohol in that standard drink/unit.
1 USA standard drink = 17.7ml or 14 grams of pure alcohol
30ml (1oz) of 40% alc./vol. spirit = 1 standard drink
175ml (standard glass) 12% alc./vol. wine = 1.2 standard drinks
1 UK Unit = 10ml or 8g of pure alcohol (around the amount of alcohol the average adult can process in one hour)
30ml (1oz) of 40% alc./vol. spirit = 1.2 units
175ml (standard glass) 12% alc./vol. wine = 2.1 units
Not even the various countries in Europe can agree on a standard unit of alcohol with Spain, France, Netherlands and Poland saying 1 unit = 12.7ml or 10g of pure alcohol, while Sweden, Switzerland and Denmark say 15.2ml or 12g. In Hungary, it's a whopping 21.5ml or 17g so perhaps we should all move there to keep the number of units we consume down.
On Difford's Guide, we state "standard drink" or "units" with the appropriate value depending on what country you are in, and if IP address or other issues prevent us from doing that then we revert to USA standard drinks.