Scotch: To be called Scotch, this whisky must be made exclusively in Scotland, and spend at least 3 years on Scottish soil.
Climate: Scotland’s cool climate and long aging process shape its refined character.
Many Scotches mature often for 10, 12, 18 years or more. One reason for this extended aging is Scotland’s cool, damp climate, which makes the maturation process more gradual. In Scotland’s warehouses (often stone dunnage warehouses with earthen floors), temperatures remain relatively mild year-round and humidity is high. This slows the interaction between whisky and wood.
The Angel’s Share: The evaporation rate – known as the “Angel’s Share” – is relatively low in Scotland, averaging about 2% of the cask volume per year.
Alcohol volume goes down over time.
Because of the damp climate, water and alcohol evaporate more evenly (in fact, the spirit’s alcohol-by-volume (ABV) usually drops over time in Scotland). This gentle loss means flavors have longer to integrate and mellow. Over years of maturation, Scotch gradually develops layered flavors from the cask while smoothing out the rough edges of the new make.
Bourbon: A true American classic, primarily distilled in Kentucky, with a warmer climate that accelerates maturation.
Climate: The climate in Kentucky (where a majority of bourbon is produced) is far more extreme than Scotland’s. Sweltering hot summers and cold winters play a crucial role in bourbon maturation. In the heat of Kentucky summers, the whiskey expands and gets pushed deep into the charred oak staves of the barrel.
As temperatue changes throughout the seasons of the year, the whisky expands and contracts, moving in and out of the wood, bringing those extracted flavors back into the liquid. The result is that bourbon can develop robust flavors relatively quickly compared to Scotch. The new charred oak imparts strong notes of caramel, vanilla, toffee, and baking spices(like cinnamon, clove) along with a deep amber color, even after just a few years in cask.
The Angel’s Share: In Kentucky roughly 5% (or more) of the contents may evaporate each year, which is about double the rate in Scotland.
Because Kentucky climate is drier and hotter on average, water evaporates faster than alcohol in the barrel, so the proof of bourbon often increases as it ages.
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