Recently, I bought Green Spot, which is a single pot still Irish whiskey. This means it is made with 100% malted and unmalted barley and triple-distilled, i.e., distilled out to a low proof as bourbon and rye are albeit the still design for the latter is somewhat different (except for the still at Versailles, KY). In the past, very small amounts of rye, oats or wheat were also used in the mash for Irish pot still, but not today. The amounts were very small again and it is not clear why they were used, I think I read once it might have performed a filtering function of some kind.
I was struck in tasting this Irish whisky in the similarities to a lot of younger rye whiskey such as Rittenhouse and Pikesville, and also Jim Beam Rye. Even the yellow colour of e.g. Jim Beam Rye (if still sold, not sure) is very similar to that of Green Spot. Of course barrel aging explains colour but it also determines taste and I think the classic flavour of both kinds of whiskey originally was not to be too old. Aged rye did become a kind of specialty and I guess there was always some very aged Irish whiskey. Still, the taste of both forms of whiskey seems to me to converge more when each is only a few years old (say, 4-7) and at that age they bear the most resemblance.
I would guess that even though it is often said the Western Pennsylvanians counted numerous ethnic groups, the Scots-Irish, who were very prominent in early settlement days in PA, must have brought a whiskey heritage with them that was reflected in their rye whiskey. Distillation was practiced by people of many origins but I believe stylistically, Irish whiskey probably provided the model even though this cannot be proved due to paucity of early records and the dampening effect on historical study of 19th century Temperance attitudes.
Rye and barley are both grains and both are used raw to a significant extent in the respective mashes. True, methodical barrel aging was not known in the 1700's in Ireland or here but the key there is methodical, artisans surely often stored whiskey in wood - the only way to ship it - and must have known that some kind of aging improved the whiskey. And those early barrels and into the 1800's weren't always charred and perhaps not typically charred - Canadians never used charred barrels exclusively to age their flavouring rye whiskies even though is a lot of lumber in Canada.
And so I think that American rye was likely a kind of emulation of Irish whiskey, the best of it as known at the time but also the white whiskey which was a counterpart to potcheen. Bourbon is a further development of rye and therefore has more of an independent American character. Both of course are all-American, but what I'm trying to say is, I can detect more Irish lineage in straight rye than in bourbon whiskey.
To this day in Pittsburgh expressions are used that are known in what is now Ulster and parts of the Scottish Lowlands whence the Scots-Irish partly came originally. That heritage is there in the language and the surnames and I think too it lives on in extended form in the sense of the younger Kentucky rye. Wild Turkey Rye is an excellent example IMO: once again that yellowish, toasty, minty, oily taste.
Gary