Why is refrigerator ice different from hotel ice?

If you have time, take a glass of water and filter it. Unless you are still using dilapidated water-drawing facilities or a rather dirty cup, then we can think that this glass of water is very clean. You may say that some invisible substances will fall into the water from the air, but this is not enough to explain why your frozen ice is like being stuffed into half a cloud.

In fact, the answer to the puzzle is the temperature of water. You see, at room temperature, many impurities are dissolved in water. At this time, you will think of high school chemistry that the higher the water temperature, the higher the solubility of solute in water. Sugar, for example, only needs a little energy to break the intermolecular force and make it dissolve in water. Therefore, as long as your water is hot and contains more energy, it is easier to dissolve sugar.

This principle also holds true in ice cubes. When you keep the cooling water, the impurities dissolved in it will gradually separate from the liquid and eventually form impurities visible to the naked eye.

Now you may ask again, why do all these impurities enter the middle of the ice instead of the surface of the ice? At this time, because water begins to crystallize when it freezes, this process is from the outside to the inside. When the external temperature drops first, impurities are squeezed into water with relatively high internal temperature. Until the water inside finally freezes, impurities have nowhere to escape and precipitate in the innermost part. In fact, this is also a method of purifying water, forcing impurities into it to concentrate, leaving only the water outside. )

This is why when it is semi-frozen, the ice that is not completely frozen in the middle is very transparent.

So what are these impurities and how did they come from? The most important things are scale, fluorine, calcium and some organic substances (most of these impurities are good for people, such as calcium and magnesium). Heating, softening and filtering water are the third way to remove them, which is why heating and filtering really help to increase the transparency of ice cubes.

However, as mentioned above, even if you completely filter out all impurities, you can't guarantee perfection, because in the process of water freezing, small bubbles will be generated, and these bubbles will be trapped in the ice like impurities. Professional ice makers freeze water in the interlayer, which can prevent air from entering the ice to some extent. Moreover, the ice maker freezes ice slowly, and the setting problem is usually higher than that of the refrigerator at home, so there is enough time to let the air out.