The ale is distilled in a copper pot-still, a process that has remained unchanged for hundreds of years. The distillate is matured in oak casks for anything from five to fifty years, though most malt is bottled at around ten years old. There is general agreement that malt whisky is at its best at about that age, though it can continue to improve thereafter. Most however, does not, and there comes a point at which the whisky in cask begins to deteriorate. Once the whisky is bottled, it does not change, provided the bottle is kept sealed.
Most malt whisky is used in the production of blended whisky.
The latter is a mixture of malt whisky and grain whisky, the quality of the blend usually depending on the proportion of malt used. Grain whisky is made in a patent still in a continuous process, from a mash which contains some barley, but mostly other grains. Blended whisky tastes quite unlike malt whisky and is usually taken over ice. More of this anon. Until the patent still was introduced in the 1840s, all Scotch whisky was pot-still whisky, though by no means all of it was malt whisky as we know it today.