I know that, in general, Scottish whiskey is peaty because of the way they dry the malt with peat smoke while Irish whisky is not because they use unpeated malt. Is the difference legally established in these two countries or is it convention? Can an Irish distillery make Scottish whiskey and vice versa?
An Irish Whiskey is distilled in Ireland and aged for a minimum of three years in oak barrels.
Thus an Irish distillery can not produce a Scottish whisky!
However our question does not end here because the Scotch Whisky Regulations 2009 define five categories of Scotch Whisky:
•Single Malt Scotch Whisky: A Scotch Whisky distilled at a single distillery using only malted barley.
•Single Grain Scotch Whisky: A Scotch Whisky distilled at a single distillery.
•Blended Scotch Whisky: A blend of one or more Single Malt Scotch Whiskies with one or more Single Grain Scotch Whiskies.
•Blended Malt Scotch Whisky: A blend of Single Malt Scotch Whiskies which have been distilled at more than one distillery.
•Blended Grain Scotch Whisky: A blend of Single Grain Scotch Whiskies which have been distilled at more than one distillery.
But some Scotch Whiskies have a smoky flavor which originates from the peat fire over which the green malt is dried, prior to grinding and mashing.
Hold on for one moment, "in Ireland, whiskeys distilled at Cooley are only distilled twice, and they make smoky whiskeys there too (Connemara)."
Thus the question as what the differences are between an Irish Whiskey and a Scotch whisky, other than how one spells whiskey remains a question of geography!
The answer is partially historical. In the 1900's Ireland's distillery market was hit hard. Starting with the Irish War of Independence from 1919 to 1921, prohibition in the United States between 1919 and 1933, then a trade war between Ireland and Britain from 1932 to 1938, and finally WW2 starting in 1939. By the 1970's Ireland only had two distilleries, Midleton which made Jameson among other things, and Bushmills. So what we think of Irish whiskey is based largely on what two distilleries were making and what they could sell. Ireland's spirits economy has finally started to recover with the number of licensed distilleries doubling between 2014 and 2016, from 9 to 18. Today there are over 30, and eventually the limited perception of Irish whiskey will change as more small distilleries do new and exciting things.