How to make clear ice cubes

Ice maker in a home refrigerator is inevitably foggy and opaque because the water that comes out of the tap contains dissolved air (about 0.003% by weight). When the water in the ice box drops below freezing, the water at the edges of the ice box compartments begins to crystallize into ice. This part of the ice is pure ice and contains very little air. Because the solubility of air in ice is very low, the remaining liquid that has not yet frozen can still dissolve air in it.

According to data from the Snowsman Refrigeration Research Center, once the concentration of air in the water reaches 0.0037% by weight and the temperature drops to -0.0025°C, a new reaction will immediately begin. At this time, as the water freezes, the air is forced out of the liquid. At this temperature and pressure, the natural state of air is gas, so they form bubbles in the ice.

Commercial ice machines can make clear cube ice because they use a different method of ice making. In the ice machine, a constant flow of ultra-filtered water is passed continuously through a metal finger-shaped freezer or through a metal freezing plate from above. Only a small part of the water freezes into ice in this process, while most of the rest flows away before the air concentration in it increases too much. When the frozen ice reaches a certain thickness, the transparent crystals can be removed by heating the metal finger-shaped freezer or metal freezing plate. The ice made in this way is completely transparent and beautiful.

When the water is cooled, using plastic wrap will probably help to expel the air from the water. Specifically, the plastic wrap is covered with the mouth of the polystyrene container containing the water, and the water in the container is slowly cooled from top to bottom, so as to achieve as much stratified solidification as possible. Do not use a thermos bottle to hold water, because the glass of such a bottle is easy to break.

Although this freezing method does not change the amount of gas forced out of the water during freezing, it can get a nice thick piece of transparent ice for a period of time at the beginning of stratified solidification. Continue freezing, and the ice will appear foggy white, at which point you can stop freezing.

Water contains a certain amount of dissolved gas. During freezing, these gases are forced out to form bubbles, which are then fixed in the ice cubes, so the ice cubes look opaque.

In order to get transparent ice, cold water is generally not used, and warm water is better. This is because warm water contains less gas. At the same time, the power of the ice maker must be reduced during the ice making process, which can extend the cooling time so that the gas in the water has time to diffuse before the water freezes.

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