|MadSci Network: Chemistry|
It is certainly possible for a the two components of a mixture to freeze out of solution together as intimately mixed at the molecular level as they were in the liquid state. The resulting solid is called a solid solution. Typical examples would be alloys of Gold and Platinum or Cobalt and Chromium at all concentrations or Silver and Copper which forms two different solid solutions over a narrower range of concentrations. On the other hand most mixtures such as Lead and Tin or Cadmium and Bismuth do what Water and Ethanol does when frozen. One pure material or the other freezes out first depending on its concentration in the liquid being frozen. Even when the temperature is reduced to the point that any of these latter three mixtures becomes completely solid the result is a mixture, be they ever so small, of pure crystals of each individual constituent. For a reference check just about any university level Physical Chemistry text. The details of how the freezing is done, rate of temperature decrease, stirring or not, etc. may affect the relative shapes, sizes, stratification, and so on of these crystals but they are still crystals of the pure constituents. A look at the description of the process used by the folks at Labatt (www.labatt.com) uses the word “proprietary” at about this point. Growing crystals, especially of specific sizes and shapes, is a bit of an art. Solid solutions may occur when the atoms or molecules involved are similar in size, electronic structure, and form the same crystalline structure. In the case of Water and Ethanol, though both are polar molecules and can hydrogen bond, the Ethanol molecule just doesn’t fit well into the ice structure due to its much larger relative size and shape if nothing else. Since beer is a dilute Ethanol solution the water freezes out first and as pure water. Whether it takes the proteins, polyphenols, or particulate matter along by simple mechanical entrainment or by growing around some or all of them as nucleation sites for crystal formation is apparently a beneficial, (from the consumers point of view) side effect.
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