Most household ice trays are designed to freeze little blocks of water from the outside in. Doing so has the side effect of driving impurities within the water toward the center of each cube. The finished products therefore look white and hazy in the middle.
To get clearer, more attractive cubes, some restaurants use expensive machines that freeze water very gradually , and exclusively from one side. That lets the impurities escape outward. Luckily, there are plenty of cheaper ways to make transparent ice cubes. One well-known trick involves boiling the water in advance, thus ridding it of dissolved gases before the freezing process starts.
Technically, water isn't colorless although it often looks that way. Believe it or not, the liquid has a natural bluish tint , owing to the fact that it absorbs red, yellow and orange light more easily than blue light.
But our human eyes can only observe this azure quality in deep bodies of water. This helps explain why the ocean looks blue to us while glassfuls of drinking water look transparent. It's also why big, thick glaciers adopt a royal hue.
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This will increase your odds of making pure ice instead of cloudy ones. To allow most of the air to escape, boil your water — whether you use tap or distilled water. Boiling water twice is the best way to make sure you start your ice-making journey with the best possible water. Let the water cool after the first boil, and consider covering it with a lid or clean aluminum foil to prevent any dust or other bits of dirt from spoiling your project.
Once your water has cooled to room temperature , boil it again and allow it to cool down before beginning the freezing process.
As the water freezes it pushes any impurities into the still-wet — that is, unfrozen — part of the water. That means that any cloudiness is concentrated in the center, the final part to freeze when you make traditional ice cubes. Directional freezing , on the other hand, is the art of getting your ice to freeze on one side first so that the cloudiness is pushed all in the same direction.
For example, if you can get your ice to freeze from the top down, all the cloudless would end up on the bottom, where it could be chipped off.
This method can result in very clear ice , and there are several ways to accomplish it. The more slowly ice freezes, the longer any air bubbles and impurities have to escape into the air instead of being trapped in the ice. Simply use your prepared, fresh water to fill your ice molds and place in your freezer, which you will crank up to the highest possible setting — about 30 degrees.
Fill the cooler no more than halfway with your prepared water and place in the freezer with the lid off. This allows the top surface of the water to come in contact with the cold air of your freezer, while the bottom portion remains insulated in the cooler. As the ice freezes, the impurities will be pushed to the bottom of the cooler. The trick is to remove the cooler from the freezer before the ice has frozen completely so that you can harvest the clear ice block and pour away the impurities with the remaining unfrozen water.
Allow the cooler to sit at room temperature for a half hour or so, or until you can lessen the block of ice. Use an old-fashioned ice pick to chip off bits of ice for drinks, or use a serrated knife to score the block into large cubes before using a mallet and chisel or your ice pick to break it up.
If you prefer regular ice cubes or ice balls made in your favorite mold instead of a giant block of ice, fill your ice trays with prepared water and place them in the cooler. Then surround your molds with more water to keep them insulated and allow the same top-down freezing method to work as noted above. First, poke a hole in each cube of a flexible ice mold.
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