Draught ale that is neither filtered nor pasteurized and has a secondary fermentation and precipitation of yeast in a vented cask in the cellar of the pub. The beer should emerge relatively clear, with a natural carbonation (albeit very light). Unworkable if the beer is chilled.

Cask-conditioned beer, often referred to as 'real ale', is brewed from only traditional ingredients and allowed to mature naturally. The unfiltered, unpasteurised beer still contains live yeast, which continues conditioning the beer in the cask (known as 'secondary fermentation'); this process creates a gentle, natural CO2 carbonation and allows malt and hop flavors to develop, resulting in a richer tasting drink with more character than standard keg ('brewery-conditioned') beers.

Real ale is always served without any extraneous gas, usually by manually pulling it up from the cellar with a hand pump (also known as a 'beer engine'). This is the traditional way of brewing and serving beer; only a few decades ago did filtered, pasteurized, chilled beer served by gas become normal.