You can learn a lot about ice just by looking at it. A pristinely clear cube tells you it’s made from pure water in a perfect crystal lattice. Cloudy ice signals impurities, absorbed gases, and irregular crystals. Those impurities (such as chlorine or fluoride) impart unwanted flavors, while absorbed gases (like oxygen and nitrogen) and irregular crystals weaken cubes, making them more prone to shattering while shaking. This creates many unwanted ice shards that will overdilute your cocktail. Bartenders go to obsessive, time-consuming lengths to achieve perfectly clear ice for craft cocktails, but we just wanted an easy at-home technique to get us as close to clear as is practical.
We started with distilled water, which cut the impurities to nearly zero. But since air dissolves more readily in cold water, we still had some big bubbles in our ice. By boiling the water and then immediately pouring it into the ice cube tray, most of that air dissipated. The ice still had a hazy center, albeit a smaller one. Insulating the sides and bottom of our ice trays using a baking dish lined with dish towels ensured our ice froze from the top down, pushing trace impurities and air toward the very bottom of our cubes. This left us with 95 percent perfectly clear cubes. We use this method to make 2-inch cubes for serving stirred cocktails and 1-inch cubes for highballs and for shaking. We used our winning brand of silicone ice trays by Tovolo, which measure about 6 1/2 inches by 4 1/2 inches; rubber ice trays also work. If you have larger trays, you may only be able to fit one in the baking dish. You can substitute filtered tap water; however, the ice will not be quite as clear.
To remove off odors from silicone ice trays, bake them at 350 degrees for 1 hour.
6 cups distilled water
1. Fold 3 dish towels in half widthwise, then stack in 13 by 9-inch baking dish, allowing towels to overhang edges. Arrange two 6 1/2 by 4 1/2-inch silicone ice cube trays in center of prepared dish. Roll up additional towels and tuck into sides of dish as needed to ensure trays are packed snugly.
2. Bring water to boil in saucepan and let boil for 1 minute. Working in batches, carefully transfer water to 4-cup liquid measuring cup, then pour into trays. Let cool completely, about 30 minutes; you may have extra water. Place baking dish in freezer and let sit, uncovered, until ice is completely frozen, at least 8 hours.
Excerpted from America's Test Kitchen How to Cocktail. Copyright 2019 America's Test Kitchen.
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