Lambic beers are the most traditional form of spontaneously fermented beer, brewed around Brussels in the Pajottenland valley of the Senne river. Interest in the production of beer in this style is increasing worldwide, and American craft breweries have implemented similar methods for producing American coolship ales . The production of these styles of beer is like any other, with the exception that fresh boiled wort is allowed to cool overnight in open vessels, which allows it to be inoculated by native yeasts and bacteria, before it is transferred to barrels or casks for fermentation over months or years.