What is overproof rum?

Proof dates back to seventeenth-century Great Britain, where the tax authorities wanted proof of the strength of spirits because the duty varied by strength. Without reliable measurement there was no fair excise.

The early method was literally a test. A little gunpowder was soaked with the drink being tested and set alight. If it burned with a steady flame, the drink counted as 100 proof. If it did not burn, there was too much water in it.

From 1740 a safer system came into use at customs. The decisive moment came in 1816, when Bartholomew Sikes presented his hydrometer. It determined strength via the specific gravity of the mixture of alcohol and water. Two years later, in 1818, its use was laid down in law.

One hundred degrees proof was equivalent to a liquid weighing 12/13 of the same volume of distilled water at 51 degrees Fahrenheit. Converted, that comes to 57.1 per cent alcohol.

This gives the rule of thumb for old bottles: multiply the alcohol percentage by 1.75 and you have the British degrees proof. Conversely, divide by 1.75. A 40 per cent bottle was therefore 70 degrees proof.

Two things make it confusing. First, on 1 January 1980 the United Kingdom switched to alcohol by volume, and the Sikes scale disappeared. Second, the United States calculates quite differently: there proof is simply twice the alcohol percentage, so 50 per cent is 100 proof and 151 proof is 75.5 per cent.

Today overproof is a usage term with no legal meaning, usually for rum above 57 per cent, although in practice it is also used from 50 per cent. No authority sets a limit for it.

Matt Pietrek listed the range, and it is wide:

• Wray & Nephew: 63 per cent
• Plantation O.F.T.D.: 69 per cent
• Lemon Hart 151 and Don Q 151: 75.5 per cent
• Denros Strong: 80 per cent
• Sunset Very Strong: 84.5 per cent

His objection to the term is practical: these rums differ so much in strength and taste that they are not interchangeable, yet all five can appear on a menu as overproof rum. He suggests naming the origin and the style instead of just the alcohol percentage.

Annex I of Regulation (EU) 2019/787 lists 44 categories of spirit drinks and the word overproof does not appear in any of them. The category is and remains simply rum.

What the category does prescribe: at least 37.5 per cent alcohol, distillation to less than 96 per cent, no addition of alcohol in any form, no flavouring, only caramel for colour and at most 20 grams of sweetening products per litre.

What must always be stated is governed by Regulation (EU) 1169/2011. Article 9, paragraph 1, point k requires that for drinks with more than 1.2 per cent alcohol the actual alcoholic strength by volume appears on the label. That percentage is therefore the only hard, verified indication on the bottle. The word overproof next to it is a sales term.

Read the alcohol percentage on the label, because that is the only figure the law guarantees. The difference between 57 and 84.5 per cent is considerable when pouring and mixing.

Separate rules apply to taking strong bottles with you. The US aviation authority FAA permits drinks of more than 24 up to and including 70 per cent in unopened retail packaging, with a limit of 5 litres per package and 5 litres per passenger. Above 70 per cent, or more than 140 proof, they are banned entirely in both hand luggage and checked luggage. The FAA mentions 151 proof rum by name.

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