Guinness stout is made from water, barley malt, barley, hops, and brewer's yeast. A portion of the barley is flaked (i.e. steamed and rolled) and roasted to give Guinness its dark colour and characteristic taste. The brew is pasteurised and filtered. A Guinness contains 198 calories per pint (20 fl oz), which is less than what is popularly thought. Nitrogen allows the beer to be put under high pressure without causing it to be carbonated (as opposed to carbon dioxide), lending to the smoothness of the brew. The use of nitrogen is also what creates the creamy foamy head of the beer. The Original Extra Stout contains only carbon dioxide, causing a more acidic taste. If you enjoy beer, make it a priority to have a pint of this deep ruby coloured liquid, the nectar of the Irish.