Malt whisky whisky regulations require malt whisky to be made in pot stills using water and malted barley without the addition of any other cereals, and the whisky must be aged for at least three years in oak casks. The use of new barrels is not required. Caramel coloring can be added, but no other additives are allowed. Irish whiskey regulations are almost identical to Scotch regulations. Malt whiskey must be distilled in a pot still from a mash of 100% malted barley, which may be peated or unpeated in character, although unpeated malt is typically used. All Irish whiskeys must be
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