Law requires scotch to be matured for three years in oak.
That's true...just found an updated version of The Scotch Whisky Act from 1988.
This is the Scotch Whisky Order 1990 No.998
Definition of Scotch whisky
3. For the purpose of the Act "Scotch whisky" means whisky—
(a) which has been produced at a distillery in Scotland from water and malted barley (to which only whole grains of other cereals may be added) all of which have been—
(i) processed at that distillery into a mash;
(ii) converted to a fermentable substrate only by endogenous enzyme systems; and
(iii) fermented only by the addition of yeast;
(b) which has been distilled at an alcoholic strength by volume of less than 94.8 per cent so that the distillate has an aroma and taste derived from the raw materials used in, and the method of, its production;
(c) which has been matured in an excise warehouse in Scotland in oak casks
of a capacity not exceeding 700 litres, the period of that maturation being not less than 3 years;
(d) which retains the colour, aroma and taste derived from the raw materials used in, and the method of, its production and maturation; and
(e) to which no substance other than water and spirit caramel has been added.
However, before these adjustments were made the following applied for "Scotch Whisky" (Scotch Whisky Act 1988), Here it states nothing about oak:
"whisky" means spirits—
(a) which have been produced by the distillation of a mash of cereals which has been—
(i) saccharified by the diastase of the malt contained therein, with or without other natural enzymes; and
(ii) fermented by the action of yeast,
to an alcoholic strength of less than 94.8 per cent by volume so that the distillate has an aroma and taste derived from the raw materials used; and
(b) which have matured for at least three years in wooden casks
of a capacity not exceeding 700 litres.
I understand this as other types of wood were allowed in whisky maturation prior to the change of law in 1990...