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That makes sense. But the paper seems to claim that the guaiacol comes from the smoked malted barley:

> Many whiskies, especially those that are made on the Scottish island of Isley, have a typical smoky taste that develops when malted barley is smoked on peat fire. Chemically, the smoky flavour is attributed to phenols, and in particular guaiacol, which is much more common in Scottish whiskies than in American or Irish ones.

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I agree that this is where the smoky flavours are supposed to come from. So your question remains unanswered. Perhaps guaiacol is generated from intermediate compounds after distillation? From chemical reactions with the barrel?

I wasn't able to find a source in a quick search, but I wonder if (traditionally) the charring of the barrel is also done with peat.

No, it isn't. Scotch whisky can only be aged in barrels that have already been used to age liquor. Conveniently, bourbon must be aged in NEW barrels, so used bourbon barrels are the primary source used for scotch. So, the barrels are sourced for the US and thus not charred with peat.

Other barrels used for scotch are typically fortified wine products, like sherry or port. Occasionally limited releases will be aged in things like ex-rum or ex-brandy casks.

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