What is the primary origin of oak barrels used in Scotland?

The primary origin of oak barrels used in Scotland is primarily from the USA, particularly those that have previously held bourbon. These barrels are reused in the whisky-making process because they impart specific flavors that complement the maturation of Scotch whisky, such as vanillin, caramel, and oak. The use of ex-bourbon barrels is particularly prevalent due to the legal requirements in the United States that mandate bourbon to be aged in new charred oak barrels; thus, once used, these barrels are often shipped to Scotland for whisky production.

The other options reflect common sources of barrels in the broader industry but are not as prevalent as ex-bourbon barrels in Scotland. French oak is indeed used, especially for finer and more premium whiskies, but it is not the primary choice. Fresh barrels made in Scotland are generally not utilized on a large scale, since the traditional aging process benefits more from previously used barrels. Spanish oak barrels, often used for Sherry production, can also be found in whisky maturation, but their use is more limited compared to the widespread adoption of ex-bourbon barrels.