Slush machines use a mixture of water, sugar, flavor and coloring to make slush. The slush machine has a cooling system, an evaporator and mixers. The cooling system circulates refrigerant continuously through pipes, and the mixers keep the mixture in constant motion.
As the refrigerant changes from liquid to gas in the evaporator, it absorbs a lot of heat and cools the bottom of the bowl to minus 3 degrees Celsius. At this temperature, water normally freezes, but in a slush machine, the movement of the mixers and the concentration of sugar in the solution prevent freezing. The optimal percentage of sugar required to keep the water from freezing is between 10 and 15 percent. The sugar molecules slip between the water molecules and stop them from bonding and making ice crystals.
The horizontal mixer moves the solution back and forth, and the vertical mixer moves it up and down. Electric motors keep the mixers moving, and the solution is evenly cooled. The mixers prevent ice from forming by making a different part of the solution touch the cold bottom of the bowl. If ice crystals form, they get distributed around the mixture instead of floating on the top. It takes two hours for the machine to turn the mixture into slush.