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. Whisky was drunk by the lower classes until the 19th Century, when it rose rapidly in social status. The whisky which became popular in the later 19th century was blended whisky, which was usually taken with ice and soda, a custom which has continued until the present day. It is fine for its intended purpose, but unsuited to the subtlety of malt whisky, for which a sherry copita or small brandy glass is much more appropriate.