Reserving a booth at the recent Pack Expo Las Vegas trade show was an error in judgment, engineer Gerd-Albrecht Graf of Cool-System Bev. GmbH frankly admits. That's not a knock on the show itself or traffic at Cool-System's booth, which was brisk. It's just that Graf couldn't take any orders: the makers of CoolKeg self-chilling kegs maxed out capacity at the company's Furth, Germany, fabrication plant before the show. The limitation is temporary: a second keg-making facility will almost quadruple production of the reusable barrels to 280,000 units a year when it comes on line in October. Las Vegas was an opportunity to wet the pallets of U.S. brewers for the system that takes a liquid from ambient temperature to about 44