Findings made in the 1940's that stout maintained in a cask under pressure of 3 to 3.5 atmos air had improved foam texture due to dissolution of small quantities of nitrogen in it, have led to development of improved methods of storage and dispensing of this beer. If the air is replaced by nitrogen gas there is better biological stability than in air and carbon dioxide contents can be reduced. Experimental work has shown that the preferred ratio is 40% carbon dioxide:60% N2 at a pressure of 2.4 atmos. Under normal conditions, the beer is matured in bulk by the usual fermentation, centrifuged and pasteurized. The gas contents are then carefully adjusted to give the ratio mentioned and the beer is racked into sterile casks under a counter pressure of the same carbon dioxide/N2 mixture. The casks are of 50 l capacity and have a doughnut shaped gas chamber with the gas mixture at about 8 atmos. The casks are fitted with lifting handles, stacking facilities and have only one opening to the interior for emptying, cleaning and filling. During washing, filling and serving of the beer, the spear remains in place throughout. Casks can be placed up to 30 feet from the dispense point either on the same floor or in the cellar. The beer passes through a nonreturn valve and a reducing valve to a cooler, generally placed under the bar counter, then to the dispensing head. By trial and error a suitable head for the system was developed. The essential feature was the provision of a region of high turbulence in the tap which was achieved by means of a precision-mace restrictor or orifice plate containing several sharp edged holes. Two different designs of these are in use and allow the beer to be dispensed with a head which can be retained for half an hour in the glass and which has a creamy mouthfeel. The system also allows the same creamy head to be obtained from start to finish of tapping of the cask.
Keywords: beer carbon dioxide dispensing flavour foam nitrogen stout