Prior to a recent business trip to London, I asked a friend for recommendations of British beers to sample.  He mentioned a few different names, and then advised me against cask ales, unless I enjoyed “warm, yeasty beers.”  Ever curious, I did sample a few cask ales on that trip, and enjoyed them enough to investigate further.

Cask ale, also called “Real Ale,” is an unfiltered and unpasteurised beer.  Cask ale starts off the same as any other beer, with traditional ingredients and a primary fermentation.  It is different from other beer because it undergoes a secondary fermentation conditioning and is served from a cask without additional nitrogen or carbon dioxide pressure.

After the primary fermentation, instead of being filtered or pasteurised, a cask ale is poured into the cask in its natural state, leaving behind most of the yeast except a small amount which is carried over in suspension to continue its work in the cask.  Finings – substances like egg white or milk – are added to the cask to drop the yeast and clarify the beer.  Additionally, priming sugars (for enhanced fermentation) or extra dry hops (for flavour) might be added to the brew.  Then, the beer “conditions” for some amount of time: shorter periods of days to weeks for lighter beers, longer periods like months for stronger beers.

After arrival at a pub, a cask must be left alone to clarify for 24-48 hours at temperature of 55-55 degrees.  Once the beer is settled, a soft spile is knocked into the shive (a small hole) in the cask.  A spile is a wooden peg that allows carbon dioxide to escape while controlling flow of air into the cask.  Once the bubbling around the spile, which indicates escaped carbon dioxide, has subsided, the soft spile is replaced by a hard one that does not allow air exchange, and the cask is allowed to settle once again.  This work with the spiles requires some skill to bring the beer to an appropriate level of carbonation.

Later, the pub will tap the cask.  The beer must be siphoned from the cellar by means of a “beer engine” or hand pump.  The pump is an airtight piston chamber; when the bartender pulls down on the handle, it raises the piston which drags up the beer.

Brewing cask ale can be a delicate process that is very sensitive to temperature changes and handling.  However, I found that cask ale offers a distinctive, well-rounded taste – particularly in the winter months.  Additionally, cask ale is fresh, natural and local, making it one of the more friendly beers to sample.