Chilling your wine with salt

The Kitchn recently had a post about how to chill a warm bottle of wine quickly using salt.

There is an interesting little debate in the comments section about the science behind this phenomenon and the use of an ice/water mixture vs. ice in cooling wine. I'll take the liberty of giving you the DL on what's up.

First off, a ice/water mixture will cool the bottle of wine faster than ice alone. Why? It has to do with energy transfer (thermodynamics to the rescue!). In order to chill the wine, the heat in the bottle of wine needs to be transferred to its surroundings. This will only happen if the surroundings are colder than the bottle (obvi.). Liquids are better at transferring heat energy than gases (like air). If you pack some ice around a wine bottle, there are many pockets of air insulating the bottle from the ice. If you add some water, the liquid flows into these pockets, contacts the wine bottle, and begins to absorb the bottle's heat energy, cooling it.

So why add ice at all? Basically, to cool the water that's cooling the wine bottle. Ice is a crystal of water molecules. Melting of ice requires breaking up the ice crystal, which requires energy. This energy is taken from the surrounding water, dropping the temperature of the water to about the melting point of the ice. Good contact with this cold water will quickly chill the wine bottle.

Where does the salt come in? Well, adding salt to this system lowers the temperature, cooling the bottle faster. This is the same principle at work when you make ice cream in an old-fashioned hand crank machine or when you salt your driveway when it's icy. Adding salt to the water lowers the freezing point of the mixture. Once you add salt, the freezing point is now lower than the temperature of the mixture. More melting than freezing begins to occur, which means that the system is absorbing more energy than it releases, so the mixture cools. That's why ice water with salt is colder than ice water without.

Another note: the water will cool the bottle faster if you re-distribute the warmed water by agitating the bottle a little as it cools. This ensures that the bottle is always in contact with cool water by mixing up the water and ice in the container. It's also why a frozen item will thaw much more quickly in moving cold water than in will hot water, but perhaps that's another post...