Cask Ale is beer that's fermented in a ferkin or cask and then served out of the same container instead of a keg. These casks aren't pressurized or force-carbonated by CO2 or nitro, and they don't have CO2 to push the beer through the lines. They rely on the natural fermentation of left over yeast during secondary fermentation to provide carbonation and a gravity fed pump system to "pull" the beer out of the casks. While the brew is served, the yeast slowly starts to fall to the bottom of the cask and become inactive. This means the beer has a shelf life, so cask beer should always be fresh. Every pub that we went into for lunch or dinner had a set of pulls for cask ale, right alongside their normal tap lines.
Beer is supposed to be served between 50 and 55 degrees Fahrenheit in the UK. This is because cask beers were originally just stored underneath the bar in a cellar type basement. There was no refrigeration, so the beer just stayed as cold as the area where it was stored and the overall temperature depended a little bit on the season. Now it's become the standard for most cask conditioned ales here and in the UK.
The lack of carbonation is also intentional, but it's not really a lack of carbonation. The carbonation comes from the natural fermentation of the beer just like it does in bottle conditioned beers or home brews. This makes it a much softer carbonation, instead of the having the harsh carbon-dioxide that most American beers on tap have. It makes the beer less filling and leaves you less gassy. In the UK, beer is expected to have between 1/4 inch and 1/2 inch of head on top of the beer. This is much lower then the level we've come to expect here in the states, especially if you're looking at some of the macro lagers that we see. Big head tends to release a ton of aroma, the smaller lighter head forces the beer's flavor to shine through.
When I got back I had to ask Cameron Fila, the head brewery at the Union Brewing Company, why they chose to do cask ale, since we don't see it very often. He said
"My wife and I took a trip to the UK and I fell in love with the beer.
I found that cask ale really was alive. The hops were more distinguishable, yet subdued by the creamy malt backbone. To me, cask ale was what craft brewing was really about, letting the brewer's hand and the premium ingredients shine through.
I came home, and knew this was the direction I wanted to go in. In many ways, it puts a lot of pressure on us in the brew house. You can hide and mask imperfections in an overly carbonated beer chilled down to the point of freezing your taste buds off, but you really have to nail a cask ale"
It's interesting from a quality stand point. I wasn't a huge fan of a lot of the beers that we had while running around your basic pubs in London, but the ones that were good were spectacular. Cameron's comments made me realize that me being disappointed was probably because of how much harder it is to mask a mediocre beer when its served at the proper temperature and there isn't much carbonation. I have been a fan of the UBC since they opened, but after touring the UK for a while, I have a new-found respect for what they do. Making such a delicious product while adhering to a very outside of the box set of style guidelines makes what they do all that much more impressive.
On top of needing an expertly crafted beer, your bar also needs to maintain high standards with the casks themselves. Casks don't last as long as kegs do because they are living beers. They have to have CO2 lightly blanket the top (but again not forcing it into the keg) to keep it fresh as long as a possible. Because the yeast is still alive the brew will continue to evolve, so a bar tender has to be careful and make sure it always tastes great. Also, without the carbonation any grime or lack of cleaning will be more noticeable.
If you've never tried a cask beer, get out to the UBC in Carmel, because they've made maintenance of their system just as important as brewing quality beer. It's the best place in central Indiana to make sure your first experience is a good one.