When we talk about "peatiness," we're really talking about the phenolic levels.Scotch is made by soaking barley in water for a couple days, which lets it "malt," or germinate for awhile before drying. The drying part is when the phenols enter the picture, since traditionally the malted barley was dried with, you guessed it, peat fires--a pretty unusual way to dry malt. That's why scotch has that trademark bitterness and other, otherwise similar whiskies (like bourbon and Irish whisky) do not. When we talk about "peatiness," we're really talking about the phenolic levels--they're highest in scotches from Islay, like Lagavulin and Laphroaig, up to 50 parts per million. The phenols are absorbed into the malted barley during the drying process (they basically get smoked), which is fermented and distilled, and, eventually, turned into a whiskey with a distinct phenolic tang.