According to Irish law, Irish whiskey must meet certain specifications:
* must be distilled on the island of Ireland
* from a mash of malted cereals with or without whole grains of other cereals
* saccharified by the diastase of malt
* fermented by yeast
* distilled at less than 94.8% ABV
* aged for at least three years in wooden casks
* Only additives allowed are water and plain caramel colouring (E150a)
Department of Agriculture’s 2014 technical file for Irish whiskey.
Once made in this way, we find that there are four main types:
* Single malt Irish whiskey
Made entirely from malted barley, in a pot still, in a single distillery. Much like the classic, unpeated Scotch.
* Single pot still whiskey
A mixture of malted and unmalted barley, made in a pot still, in a single distillery. Includes raw, unmalted grain in the mash. If I understand correctly only 5% (by mass?) of grains other than barley may be be used.
* Grain whiskey
Made in a Coffey still, rather than a pot still. Could be made from any grain, likely barley, corn, wheat or rye. Lighter and more neutral in taste, grain whiskey doesn’t have the amound of organic compounds normally found in pot still whiskey, so it is sometimes criticized as being midway between whiskey and neutral grain spirits (“vodka”.) Rarely sold on its own. Rather, grain whiskey is usually blended with either Single malt or Single pot still whiskey. When this happens it is sold as blended whiskey.
* Blended whiskey
Any mixture of the above styles. This is now the most common style of Irish whiskey.
Apparently so! The rules state that this is “subject to the maturation of the final distillate for at least three years in wooden casks, such as oak, not exceeding 700 litres (185 US gal; 154 imp gal) capacity.”
“Technical file setting out the specifications with which Irish whiskey / Uisce Beatha Eireannach / Irish Whisky must comply.” Food Industry Development Division Department of Agriculture, Food and the Marine October 2014.
The earlier Irish definition is from Irish Whiskey Act, 1980, which stated “the spirits shall have been matured in wooden casks – in warehouse in the State for a period of not less than three years”
Controversies in Irish whiskey
Some whiskey sellers advertise and sell their products as if they are a distillery, but they are actually NDPs (non-distiller producers); they have bought whiskey from elsewhere, blended it, and perhaps finishing them by giving additional aging in different barrels. There’s nothing inherently wrong with this – but some companies aren’t clear about being NDPs, and customers deserve to know if the whiskey inside the bottle is really distilled by the people selling it.
Another excellent article on this topic: