Reading a book on american whiskey today (The Book of Classic American Whiskeys, Waymack & Harris), I came across this passage:
Not all that happens in the barrel is easily understandable. For example, the alcoholic strength of barrels is apt to change during the aging process. In the Scotch industry, the whisky, aged in Scotland, of course, tends to lose alcoholic strength. But in the American whiskey industry, it tends to go the other way. Especially in barrels located in the upper ricks of the open warehouses, the alcoholic proof rises year by year.
What the... ? Does this mean the angels in Kentucky are more moderate in their alcohol intake?
Interestingly, the authors state there is no commonly accepted reason for the discrepancy, giving several competing theories from distillers around the area that carried very little weight - e.g., the 'osmosis theory', that water molecules are smaller than alcohol molecules and can more easily gain passage through the oak. Nice theory, but it doesn't really explain why the opposite is true in Scotland - maybe peat makes water molecules bigger? Anyway, the book is about a decade old and I was wondering if anybody had heard any sort of explanation for this phenomenon.