Ask Dr. Beermeister

Q. I like several beers that should be fermented using lager yeast (such
   as Bock) but am not set up for lagering.  Can I make these styles anyway?
   What would the taste difference be if I make a "lager" using ale yeast?

A. Yes, you can use the ingredients for a lager recipe and ferment with
   either a lager or ale yeast at warm (ale) temperatures and make very
   good beer. Unfortunately, it won't smell or taste like the traditional
   lager that you want. At cool temperatures, lager yeasts ferment slowly
   and cleanly producing alcohol and carbon dioxide.  This same yeast, or
   an ale yeast, at warmer temperatures acts very differently. At higher
   temperatures yeasts have the energy to produce more complicated alcohols
   and things called esters.  These compounds contribute to the "fruitiness"
   and complexity to the nose and flavor of a rich ale.  Unfortunately, this
   is not what you want in a lager.

   The best you can do is ferment your ales as cool as you can. Put your
   carboy in a tub of water and wrap it with an old towel or T-shirt.
   The evaporating water keeps the carboy several degrees cooler than room
   temperature and will reduce the production of esters, especially if you can
   get it down close to 60 F.  Besides, carboys look sexier in wet T-shirts!