I just went on a guided tour of Glenkinchie distillery this last weekend. There’s more things that influence the taste of whisky (to take one example) than I had thought:
The choice of grain: most whisky production in Scotland uses barley (i.e. all single malts). A small percentage uses other grains, such as wheat and maize, and is used in making blends.
The method used to stop the malting process/roast the grain. Lowland whiskys used a coal or wood fire to toast the malted grain, as this was the fuel source most readily at hand. Island and highland malts used peat, as there wasn’t a large amount of trees available on the islands, and peat was plentiful. Peat imparts a smoky flavour to the malted grain which is carried through into the whisky.
The amount of fermentation time and specific strain of yeast used. Glenkinchie has a very short fermentation time, and the specific strain of yeast is a trade secret, with the distillery floor workers kept in the dark.
The size and shape of the distillation pots. As seen in this photo from inside the distillery, Scottish stills have a collar around them that influences the taste (though the mechanism through which this happens is apparently not fully understood). I think the guide stated that Irish and American stills are typically a different shape. Incidentally, those stills are the largest in Scotland, and by law are solid copper. They’re replaced every ten years with a brand new set, exactly the same size.
I think Scottish malts are typically distilled twice. Irish are triple distilled (I think? I remember Jamieson’s making a big deal out of this?) and this will also affect taste.
The aging process. Glenkinchie uses second hand barrels imported from America which have previously held bourbon, and also import sherry barrels from the continent. These impart a lot of taste. Also, the number of years that the spirit ages affects the taste (I suspect this is where most of the taste comes from: we were showed the whisky safe with the distilled spirit coming straight out of the stills, it looked like water, and nothing like whisky).