The Classic Liquor That Benefits From Fresh Vanilla Bean
Vanilla beans are a potent fresh spice that can be used to flavor everything from ice cream to oil. Another prime use for vanilla beans is flavoring alcohol, particularly whiskey. To do this, simply slice the vanilla pods lengthways (use between one and two pods for every 8 ounces of liquor) and pop them into the bottle. Leave it to infuse for a couple of weeks, tasting the whiskey daily. You can remove the pods when the flavor is to your liking.
One of the main reasons whiskey responds so well to fresh vanilla beans is that it already contains vanillin, a compound that carries the taste of vanilla. This compound comes from the oak barrels whiskey is aged in. (Whether these barrels are old or new is one of the key differences between bourbon and whiskey.) This means that infusing whiskey with vanilla beans simply enhances flavors already found in the liquor.
There is one problem with adding fresh vanilla beans to whiskey: it can unbalance the liquor. This is not so much of a problem if you are infusing a whiskey that's either mild or already unbalanced, but if you are planning on infusing a well-aged, expensive, and balanced whiskey, you might want to reconsider. Even adding a couple of vanilla pods could throw the entire bottle out of whack. Instead of risking a wonderful whiskey, feel free to first experiment with whiskeys or bourbons that aren't that great.
Other ways to infuse whiskey
Thanks to the huge number of flavor notes that whiskey contains, many ingredients can be used to infuse the liquor without completely altering its character. These include herbs, nuts, and even vegetables. Perhaps the most effective, however, is citrus peel, particularly orange peel. Adding some orange peel to your whiskey for a few days will exacerbate the spirit's fruitiness and add a lovely undertone to it. This is particularly useful if you find yourself stuck with a bottle of whiskey that is quite harsh or unapproachable.
Another way of infusing whiskey that has gained a lot of popularity in recent years is fat washing. This involves melting fat or rendering it from an ingredient, often bacon, allowing it to cool slightly, and then adding it to the whiskey. After letting it infuse for a few hours, you remove the fat by either chilling the whiskey and discarding the solidified fat or by pouring the chilled whiskey through a coffee filter. The effect this process has can be pronounced. As one person noted on Reddit: "The fat washing has completely transformed the [whiskey's] finish, and it's greatly improved the mouthfeel and smoothed out any harshness." To put it another way, fat-washed spirits and cocktails are absolutely delicious.