澳门金沙平台开户网址在哪里:Technology: The extra ingredient in a can of draught Guinness

 作者:黄湎     |      日期:2019-03-04 03:13:07
By ANDY COGHLAN GUINNESS, the maker of the black, creamy beer for which Ireland is famous, has managed the impossible. The company has succeeded in canning a form of Guinness that, until recently, was available only on draught in public houses and restaurants. The world’s seven million Guinness lovers have a choice between two products: draught Guinness, a thick, smooth stout with a creamy-white head and Guinness Extra, which is available in bottles and cans. Guinness Extra has a coarser texture than draught Guinness and a head that is less smooth and creamy. According to Alan Forage, the product development director at Guinness, the majority of people who drink draught Guinness do not drink Guinness Extra. ‘We knew that draught Guinness in cans would give them the opportunity to enjoy their favourite brand at home as well as in the pub,’ he said. Forage and his colleagues began working to solve this problem in 1984. After four years of development work, costing Pounds sterling 5 million, Forage and his team had perfected a tiny diaphragm, made of plastic, that cracked the problem. They tested more than 100 different techniques before settling on the so-called ‘in-can-system’. People who buy draught Guinness in cans, which have been available throughout Britain since March, will find this system if they slice open the empty can. The device, which sits on the base of the tin, helps to mimic the tap in the pub. Draught Guinness owes its creamy texture to a surge of bubbles in the beer as it passes through a series of tiny holes in the special dispensing tap. The tap has a system of tiny holes which creates pressure differentials. These differentials force the gases out of solution and produce a ‘surge’. Unfortunately, the gases will remain in solution if people simply pour Guinness from the barrel into a glass. The new system essentially mimics this process from the inside of a can. The device is a plastic chamber with a minute hole at the top, which sits on the base of the cans. For the system to work, the pressure in the can must exceed atmospheric pressure. The canners fill the can with beer that is cold enough, at between 0 Degree C and 1 Degree C, to retain gas that would bubble out of solution at higher temperatures. The canners put 440 millilitres of Guinness in a can that can hold 500 millilitres, in order to leave enough room for the creamy head to form. They also ‘dose’ the beer with extra nitrogen, which raises the pressure when the can is opened. Once the lid is on, the pressures in the can and inside the chamber reach an equilibrium that forces beer and gas into the device. When someone opens the can of beer by pulling the ring-pull, it initiates the same process that happens in a tap for draught Guinness. As the ring-pull comes off, the resulting drop in pressure forces beer and gas out of the chamber through the tiny hole, creating small, stable bubbles. As the bubbles rise up through the liquid, they act as centres where other bubbles form. This is what causes the characteristic surge. The number of bubbles created and the diameter of the bubbles dictates the density of the head of the drink and its creaminess. The smaller the bubbles, the creamier the texture, says Forage. The only remaining problems for the designers related to the canning process. They had to invent a filling device that expels oxygen from the can, because the gas impairs the flavour of the beer. Now, Guinness has patented the system and owns the registered designs of all the engineering equipment that is unique to the packaging line. The secret for drinkers, says Forage, is to make sure that the can is cooled in the refrigerator for two hours before serving. Otherwise,