This rare discontinued expression of Aberlour single malt was bottled at 57.1%, or 100 proof. While over in the United States the proof system still reigns supreme, the traditional British proof has been obsolete for some decades. In the olden days, before any official measuring systems were introduced, it was difficult to confirm the alcohol content of whisky. To prevent fraud on the part of whisky makers, the gunpowder method was invented. The whisky was mixed with gunpowder and then ignited. If the mixture could burn, the whisky was rated ‘proof’. 100 proof corresponds to about 57% ABV.