A cool cellar temperature (think 50 - 54 °F) is a wonderful temperature at which to drink a cask ale. It's refreshing, yet no so cold as to mask flavor. Room temperature, on the other hand? That's not so refreshing: inappropriately warm for any beer.
And, then, what of of a summer day? Beer at 80+ °F? That's unpalatable, and a problem. More and more outdoor beer festivals in the U.S. have begun featuring casks as part of their beer lineups. Many of these festivals are held in the summer months. So, what to do?
The classic method is to use a wet towel draped over a cask. It's not so much the temperature of the towel that cools the cask, but a process called latent heat vaporization ... or in simpler terms: evaporative cooling. Water requires significant energy to go through a phase change from from liquid to gas (steam). As the water evaporates off the towel, it (the water) is absorbing a lot of energy (heat) from the cask. That energy transfer is what keeps the beer cool. (The human body sweats on a hot day for a similar reason.) Of course, a dry towel accomplishes little. Any cooling requires regular re-moistening of the towel.
And, a dry, cool day.
At the high heat and humidity of a summer afternoon in the lower 48 states, draping a wet towel over a cask is a futile refrigeration method. Using an ice blanket, or a simple bag of ice, draped over a cask will work but marginally better. The ice will chill only the top layer of beer. As more and more beer is served from the cask, it will be the uppermost layer of AIR in the cask that will be chilled, NOT the beer.
So, again, absent cooling coils and refrigerators, how to keep a cask cool on a hot and humid day? Here's a method I've employed to good effect.
- An hour before service, c-a-r-e-f-u-l-l-y submerge the cask upright in ice. (Don't worry!)
- Vent and tap through the keystone bung.
- Insert a cask widge or ale extractor.
- Pull the beer via a beer engine.
This photo, by the way, shows the use of an ale extractor: a rigid tube that also doubles as a tap and vent. It's a cask tool of older pedigree, and works well, but it is not quite as versatile as a Cask Widge.