Simply put, pressurised air is used to force the beer up to counter dispensers. Oxidation is not noticeably increased by this method but there is a small increase in the condition of the beer. This is the correct term for the device commonly seen in British pubs which pumps beer from the cask to the bar. Also known as a handpump or beer pump . It can't be emphasised enough that you should use the correct beer engine for the style of beer.
Beer engines have two styles of neck, the swan neck and standard neck .
Swan necks do untold damage to beers with a flowery hoppy aroma knocking the aroma out of the beer. The second feature which affects the beer is the sparkler. Sparklers force the beer through many small orifices producing a tight frothy head on the beer. The result of this is of course, that Southern beers are not served with a head. Southern beers served in the northern manner are lifeless travesties of beers, whilst served in the proper manner they are a revelation, a wholly different beer.