Draught or Draft beer is almost always un-pasteurized and therefore is more fragile. It should be consumed after being "tapped", and is generally truer to the flavors of the ingredients as pasteurization exposes the beer to heat and changes the flavor profile. A keg has a concentrically located downtube and a valve that allows beer in and gas out when filling and vice versa when beer is dispensed. Also kegs have a simple concave bottom. This aspect of keg design meant that all the beer in the keg was dispensed which therefore required that the beer be processed by filtration, fining or centrifuging, or some combination of these, to prevent sediment formation. Lastly, kegs have straight sides unlike the traditional barrel or cask shape. In order to get the beer out of a keg and into a customer’s glass, it can be forced out with gas pressure, although if air or gas at low pressure is admitted to the top of the keg it can also be dispensed using a traditional hand pump at the bar. By the early 1970s most beer in Britain was keg beer, filtered, pasteurized and artificially carbonated. This change was largely driven by the customer's dislike of sediment in his beer.