Scotch whisky whisky used. An age statement on the bottle, in the form of a number, must reflect the age of the youngest whisky used to produce that product. A whisky with an age statement is known as guaranteed age whisky. Scotch whisky without an age statement may, by law, be as young as three years old. In the early 21st century, such "No age statement" whiskies became more common, as distilleries responded to the depletion of aged stocks caused by improved sales. Labels may also carry various declarations of filtration techniques or final maturation processes. A Scotch whisky labelled as "natural"
Whisky in wood for a similar time. After a decade or two, additional aging in a barrel does not necessarily improve a whisky. While aging in wooden casks, especially American oak and French oak casks, whisky undergoes six processes that contribute to its final flavor: extraction, evaporation, oxidation, concentration, filtration, and colouration. Extraction in particular results in whisky acquiring a number of compounds, including aldehydes and acids such as vanillin, vanillic acid, and syringaldehyde. Distillers will sometimes age their whiskey in barrels previously used to age other spirits, such as rum or sherry, to impart particular flavours. Most whiskies are sold