While it lowers the mp of water as stated earlier (a colligative property), more importantly, the dissolving process (measured by heat of solvation) is endothermic. It takes energy to separate the ions in the salt (solute). That energy comes from the solvent (water).
Therefore, the solution cools. (BTW, the salt goes into the cooling or refrigerant bath, not the edible product itself).
If you start with ice water(0 C), then you end up cooler than zero. At those temps, the fatty emulsion of protein and water (aka cream) (as well as sugar and flavoring) solidifies.
Yum, yum and enjoy.Why do they use salt in the process of making ice cream?
well, when in junior high we did that experiment, the salt helped the ice cream to freeze more fast... in other words making the ice more colder, because salt has the property of lowering the temperature of ice very fast, it has to do with intermolecular forces.
The salt lowers the freezing temperature of water. Putting in the salt will allow the temperature to go down more before freezing.
If you live in a place that has lots of snow and ice in the winter, then you have probably seen the highway department spreading salt on the road to melt the ice. You may have also used salt on ice when making home-made ice cream. Salt lowers the freezing/melting point of water, so in both cases the idea is to take advantage of the lower melting point.
Ice forms when the temperature of water reaches 32 degrees Fahrenheit (0 degrees Celsius). When you add salt, that temperature drops: A 10-percent salt solution freezes at 20 F (-6 C), and a 20-percent solution freezes at 2 F (-16 C). On a roadway, this means that if you sprinkle salt on the ice, you can melt it. The salt dissolves into the liquid water in the ice and lowers its freezing point.
If you ever watch salt melting ice, you can see the dissolving process happen -- the ice immediately around the grain of salt melts, and the melting spreads out from that point. If the temperature of the roadway is lower than 15 F or so, then the salt really won't have any effect -- the solid salt cannot get into the structure of the solid water to start the dissolving process. In that case, spreading sand over the top of the ice to provide traction is a better option.
When you are making ice cream, the temperature around the ice cream mixture needs to be lower than 32 F if you want the mixture to freeze. Salt mixed with ice creates a brine that has a temperature lower than 32 F. When you add salt to the ice water, you lower the melting temperature of the ice down to 0 F or so. The brine is so cold that it easily freezes the ice cream mixture.
Ice has to absorb energy in order to melt, changing the phase of water from a solid to a liquid. When you use ice to cool the ingredients for ice cream, the energy is absorbed from the ingredients and from the outside environment (like your hands, if you are holding the baggie of ice!). When you add salt to the ice, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment in order for the ice to melt.
Lowers the freezing point of water, so if you mix salt with ice cubes, you get super-cooled water, which helps to freeze the ice cream better
Do they actually put salt in the ice cream?
It is very important to reduce the ice cream mixture or slurry to a temperature below 0 degrees Celsius. Plain old ice water is about at that temperature. When you add salt to the mixture, the vapor pressure of the water is depressed, and so is the freezing point. That makes the ice-salt mixture lower than zero degrees, and enables the slurry to ';solidify'; into what you like, rather than cold cream soup.
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