By definition, an ice cube is just a unit of frozen water; but to a bartender, a distiller, or a spirits aficionado it can be a sacrilege—the enemy of all that is good and sacred about liquor. When it comes to spirits, ice really does have transformative powers, and while those powers can be used for good, they can also lead to evil. When you add ice to a spirit-filled glass, the change in temperature and the addition of the water alters the flavor of what you’re drinking. On the plus side, you’ll wind up with a smoother libation. Consequently, you’ll lose some richness and depth. If you’re unsure as to when you should use ice, consider this a cheat sheet for the next time you’re asked, “Straight up, or on the rocks?”
If rum is your tipple of choice, the easiest way to navigate the ice issue is with your eyes: the lighter the color, the more ice friendly your rum will be. The same rule applies to tequila. As for vodka, chilled is always preferred; but if you’re pouring gin, ice cubes are a necessary accompaniment. Gin’s juniper flavors can be cloyingly sweet and air-freshener-strip piney when it is served neat, and the other botanicals can show up as unpleasantly bitter. It takes the cooling and diluting effects of the ice to balance out and harmonize all of the botanicals.
When it comes to whiskey (or whisky, depending on where the spirit is distilled), however, there are many different factors to consider.
Single-malt fans generally are purists who eschew anything more than a few drops of distilled water to “open up” the flavors and aromas of the whisky. Those drops are also good for tamping down the alcoholic heat, which is important in the case of cask-strength whiskies, which can be in the neighborhood of 60% to 65% alcohol.
Blends are designed to be smooth, which means, in theory, they don’t need ice. Nevertheless, blended scotch on the rocks is quite popular, especially in the United States, so you won’t be skewered if you pour some over ice. There are blends worth savoring neat, of course, but blended whisky is a more social drink and, as such, it can stand up to an ice cube or two.
American whiskey (corn-based bourbon and spicier rye) doesn’t have as much of a hard-core ice-versus-no-ice dynamic, but like with scotch, the use of ice can seem a little paradoxical. Higher-proof whiskeys with rich, powerful flavors, like Booker’s bourbon or WhistlePig rye, can stand up best to the rocks. But then, if you actually add the ice, you’re rounding off the rough edges—and with great whiskey, the rough edges mean a lot. If, on the other hand, you’re drinking a whiskey that’s a common mixer (Jack Daniel’s, Old Overholt, or Jim Beam, for example), don’t be ashamed to add a cube or two. Sure, you’ll sacrifice some of the whiskey’s subtleties, but good mixing whiskeys aren’t really about the subtleties, anyway.
Canadian and Irish whiskeys aren’t as highly regarded as their Scottish or U.S. counterparts, though that’s beginning to change, especially with Irish brands like Redbreast. These spirits are lighter, smoother, lower proof, and somewhat less distinctive than single malts or small-batch ryes. However, brands like Bushmills, Kilbeggan, and Crown Royal are nothing if not versatile. If you like your whiskey chilled, you’re not painting a mustache on the Mona Lisa by adding a couple of rocks.
Japanese whiskey, on the other hand, is an exception to the rule. It’s modeled largely after scotch, which suggests that it is best enjoyed neat or with a few drops of water. However, it’s acceptable in Japan to drink even the finest whiskeys on the rocks or in a highball with ice and carbonated water. In fact, bartenders in Japan have elevated ice to an art form with the ice ball, a spherical, roughly baseball-sized chunk of frozen water that, because of its size, melts slower and dilutes less.
In the end, these accepted practices are merely what’s most popular. If you want to pour a cask-strength single malt over crushed ice and add a swizzle straw, we’ll be the last ones to stop you.