You might prefer not to think about it, but there are lots of bacteria in your cocktail on the rocks. Well, there are bacteria in the ice. But if you’re drinking whiskey, you may be better off than your clear liquor-drinking friends. A study published in the Annals of Microbiologyhas found that whiskey kills ice bacteria more effectively than vodka.

Italian researchers took 60 ice cube samples from home, restaurant, bar, and industrial sources, and found 52 strains of bacteria corresponding to 31 different species. This is particularly troubling considering we consume cocktails and other drinks with ice cubes almost every day. What’s worse is you’re only somewhat in control of the cleanliness of your own freezer. You have no idea what’s going on in the ice chest at your local bar.

The researchers deliberately contaminated ice cubes with the four most common strains of bacteria that they found, and then mixed them with vodka, whiskey, a Martini, peach tea, tonic water, and coke. They found that while alcohol, CO2, and acidic pH levels consistently reduced the presence of bacteria, whiskey was the only liquid that eliminated all 4 strains of bacteria in the ice.

The study concluded that, in addition to alcohol, it was likely whiskey’s acidity that contributed to killing all of the bacterial strains. Whiskey has a lower pH than vodka, which means it’s a more acidic spirit. So next time you’re trying to decide between a Jack or Tito’s on the rocks, you might want to go with the Tennessee sour mash.