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Wednesday, January 4, 2012

Playing the ice

Making the Alinea prescribed mango soy wafer on a home-made anti griddle. A little molecular gastronomy modernist cooking with BBQDude.

In the last post, I tried to explain how salted ice can serve as way to freeze ice cream, because it'll draw the heat (energy) out of the canister as the salt dissolves. Dissolving stuff in water - salt, sugar, proteins, alcohol - all serve to lower the freezing point of water, and the higher the concentration, the lower the temperature will have to be to freeze. That's because as water freezes and forms crystals, the water molecules line up in an orderly fashion. Dissolved molecules interfere with ice molecules interacting with itself, and thus, prevents the whole from solidifying.

But, eventually, it freezes, right? Sea water, for example, freezes to form sea ice (not to be confused with ice bergs that are actually chunks of ice from land). Well, not really. When the temperature is dropped slowly, some water molecules will find each other and form a chunk of ice - but that means that the number of water molecules in the liquid phase went down. Meaning that the concentration of salt there just went up - so the temperature has to be even lower to freeze that. Microscopically, sea ice is made up of fresh water ice with small droplets of saturated brine encased therein. Given enough time, the brine should drain out, leaving behind unsalinated water.

This phenomenon of water only crystalizing with itself in solution is exploited as a way of dehydrating and concentrating certain solutions. For example, ice wine. To make ice wine, grapes are harvested and pressed when frozen. This results in a more concentrated juice, as the ice crystals left behind are entirely water - and the more concentrated juice results in the distinctively more intense flavor of the wine. A second form of ice wine (and to some degree, ice beer) comes from partially freezing the wine after fermentation, and sieving out the ice crystals - again, concentrating the liquid.

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