http://www.camra.org.uk/about-real-ale

What makes real ale 'real'?

Real ale is a natural product brewed using traditional ingredients and left to mature in the cask (container) from which it is served in the pub through a process called secondary fermentation. It is this process which makes real ale unique amongst beers and develops the wonderful tastes and aromas which processed beers can never provide.

What's the difference between 'ale' and other beers?

MaltThere are a huge range of different beer styles, each with different qualities, tastes and strengths, but each falls into one of two main categories; ale or lager. The key difference between ales and lagers is the type of fermentation.

Fermentation is the process which turns the fermentable sugars in the malt into alcohol and carbon dioxide. Lagers are made using bottom-fermenting yeast which sinks to the bottom of the fermenting vessel and fermentation takes place at a relatively low temperature. Authentic lagers then undergo a long period of cooled conditioning in special tanks.

Ales, which includes bitters, milds, stouts, porters, barley wines, golden ales and old ales, use top-fermenting yeast. The yeast forms a thick head on the top of the fermenting vessel and the process is shorter, more vigorous and carried out at higher temperatures than lager. This is the traditional method of brewing British beer.