Real ale is also known as cask-conditioned beer and is now an accepted dictionary definition for warm-fermented ale that is not filtered, pasteurized or artificially carbonated. At the end of fermentation in the brewery, the unfinished beer is run into casks where additional hops may be added for aroma and flavour, along with finings that draw yeast and proteins to the floor of the cask.
In the pub cellar, casks are vented (allowed to breathe) by knocking porous pegs into bung holes. The beer undergoes a secondary fermentation in the cask that creates natural carbon dioxide, giving the beer a natural sparkle in the glass. The range of real ale includes mild, bitter, best bitter, pale ale, IPA, golden ale, extra special bitter, porter, stout, old ale, barley wine, wheat beer and Scotch ale.