The aging process helps to mellow out the harshness of the alcohol (such as sulfur) while also imbuing the bourbon with its distinctive flavor. The flavor notes are drawn from the wood itself; the longer the bourbon sits in the barrel, the more rich and complex its flavor profile will be.
The story goes that they would have preferred the government to create a Tennessee whiskey classification but had to settle for 'whiskey.' In the years that followed, they adopted the name 'Tennessee whiskey as a statement of product origin. That is how the designation 'Tennessee Whiskey' was born.
As the yeast eats up the sugars during fermentation, they create alcohol and CO2. But the more alcohol and CO2 they produce, the less sugar there is for them to feed on. And at a certain point (around 14 to 18% ABV), the alcohol levels become toxic for the yeast.
For over two centuries, whiskies have been mainly aged in wooden barrels. The wood absorbs some of the more unpleasant aspects of the whisky distillate (such as sulfur), and, in return, imbues the liquid with flavors unique to itself. However, during the process of aging whiskey and because of the porous nature of wood barrels, a small percentage (roughly 2%) of every barreled whiskey batch is lost annually. Traditionally, it was believed that this whiskey evaporated up to the heavens, thus, it was coined the “Angel’s Share.”
But that doesn’t mean Crown Royal whisky = rye. Unlike U.S. distillers who combine the grains before mashing them, Canadian distillers mash the grains individually and then combine them as separate whiskies. This means that Canadian blended whisky may contain zero, some, or a 50%+ rye.