The making of "ice" beers, in general, involves lowering the
     temperature of the finished product until the water in it begins to
     freeze and then filtering out the ice crystals that form. Since water
     will freeze before alcohol, the result is higher alcohol content. The
     ice forms around yeast cells, protein particles, etc. so these get
     removed as well; leaving fewer components to provide taste and
     character.

     This process is not new to brewing, having been developed in Germany
     to produce "eisbocks". Apparently they were produced by accident
     during the traditional spring celebration with bock beers. Spring,
     being the capricious season that it is, probably sent a late cold
     snap around one year causing some of the spring bocks to partially
     freeze. People drank it anyway and liked the change in flavor.

     In its current incarnation, the process is an offshoot of the
     concentrated fruit juice industry. It was developed by orange growers
     to reduce the costs of storage and shipping by concentrating the
     fruit juice through freezing and removal of some water. Labatt
     Breweries claims to have pioneered this process for brewing and most
     of the large North American brewers quickly followed suit in the
     usual marketing frenzy.

     The main difference between these "ice" beers and true eisbocks is
     taste and character. Any beer brewed using this method will only be
     as good as the brew with which you start. In other words, if you
     start with a bland, flavor-impaired, adjunct-laden beer and remove
     some of the water, you end up with a bland, flavor-impaired,
     adjunct-laden beer with more alcohol. OTOH, if you take a rich,
     malty, traditionally brewed bock and remove some of the water, you
     end up with an eisbock.