Section 6: Sale and Distribution
In common with other EC countries, on 1st January,
1980 Britain adopted the system of measurement
recommended by the International Organisation of
Legal Metrology, a body with most major nations
among its members. The OIML system measures
alcoholic strength as a percentage of alcohol by
volume at a temperature of 20°C. It replaced the
Sikes system of measuring the proof strength of
spirits, which had been used in Britain for over 160
The Customs and Excise Act of 1952 defined spirits
of proof strength as follows:
'Spirits shall be deemed to be at,proof if the
volume of the ethyl alcohol contained therein made
up to the volume of the spirits with distilled water
has a weight equal to that of twelve-thirteenths of a
volume of distilled water equal to the volume of the
spirits, the volume of each liquid being computed as
at fifty-one degrees Fahrenheit'.
In other words. proof spirit meant that the spirit at
a temperature of 51°F. weighed exactly twelve-
thirteenths of a volume of distilled water equal to the
volume of the spirit. It was, in fact. a mixture of spirit
and water of a strength of 57.1% of spirit by volume
and 42.9% of water.
Spirit of proof strength was the technical standard by
which strength was measured until 1st January,
1980. Hundreds of years ago, spirit of this strength
was proved when whisky and gunpowder were
mixed and ignited. If the gunpowder flashed, then
there was enough whisky in the mixture to permit
ignition. Such whisky was held to have been proved.
If the spirit was weaker than this proof strength
ignition did not take place.
In the 1740's. the Customs and Excise and the
London distillers began to use Clark's hydrometer, an
instrument devised to measure spirit strength. A
more accurate version by Bartholomew Sikes was
universally adopted under the Hydrometer Act,1818,
and remained in standard use until 1980.
All whisky is retailed at a minimum 40% volume of
alcohol for the home market. A strength of 43%
volume is often found in export markets.
Some U.S. proofs and their British and European
American British and
100 deg Proof 50% Alc. vol.
86 deg Proof 43% Alc. vol.
80 deg Proof 40% Alc. vol.
Cask In litres
American Barrel 173-191
The normal practice is for the blender to buy the
whisky as soon as it is distilled. It is then kept under
bond in warehouses at the distillery to mature until
the blender requires it. By law whisky must mature
for a minimum of three years. although in practice
the minimum age is much greater. After blending,
Scotch Whisky is usually returned to cask and left for
a further period of several months to allow the
constituent whiskies to 'marry'. It is then bottled for
© SWA 1995