Some states (in America) have ridiculous laws about what types of beer can be sold in various places. Often times certain types of stores can only sell "3 2 beer," or beer with no more than 3.2% ABV.
So various brewers make special, reduced-alcohol batches meeting this requirement.
How do brewers achieve this reduction in alcohol, and does it affect the taste of the resulting beer?
You're speaking of Utah, I assume, the only state I've been to that has laws like that. I know you can achieve lower alcohol content by using less yeast, or sugar, or both, since alcohol in beer is produced by the fermentation process of yeast turning sugar into alcohol. I would guess this is primarily how it's done, but there could be other (post-fermentation) processes of removing alcohol. (EDIT: according to Wikipedia, I'm totally wrong. Most low- or non-alcoholic beer is made by boiling off the alcohol.)
In terms of taste, lighter beers (in terms of alcohol content), generally taste, well, lighter. I like many higher-alcohol beers because the alcohol seems to bring out many of the more complex flavours in the beer, making it (in my opinion) more interesting. That's not to say that all strong beers are good or all light beers are bad, as there are many other things to consider. But I don't think it's possible to get the same complexity and flavour into a light 3.2% beer as it is in a stronger beer, in my experience anyway.
Any beer is only as good as the brewer's skills. In London (UK) we have a brewery producing a 2.8% abv beer (Redemption brewery, beer name escapes me) which is packed with hops and of greater hop depth than many IPAs. Batches of a beer that are brewed to be low alcohol will necessarily be different to those brewed at full strength which is why I would hope (pray?) that any brewer whose product is worth drinking would make a different beer, brewed at low strength for these markets. These beers can be as flavoursome and exciting as, if not more so than, higher strength beers. The process to make the beer lower ABV is simply reducing the amount of sugar that can be converted into alcohol by using a lower sugar content mash either using specific lower sugar malts, using less malt, or using a yeast that will not support higher alcohol concentrations (alcohol kills yeast...!). Using less yeast won't work as the given yeast will continue to multiply to make up the shortfall. If you are not making real beer halting the fermentation early by killing the yeast with heat (or similar) will produce a lower alcohol beer but it will be sweeter as there is more unfermented sugar. Fining and serving real ale before fermentation has produced a higher strength may have a similar effect for those types of beer. Since alcohol dissolves flavouring compounds better than water it is much harder to brew a highly flavoured weak beer but this may be offset by taste complexity. Larger breweries will reduce alcohol levels chemically post-production by boiling off alcohol or similar. this will reduce the flavouring compounds in the beer (see GCSE fractional distillation notes or similar for details) and so make the beer taste weaker. These are produced at mass market quantities and even the full strength product is pretty awful compared with crafted or real beers.
