Altbier is a German top-fermenting beer brewed in Düsseldorf and other parts of North Rhine-Westphalia. The name Altbier, which means old beer, refers to the pre-lager brewing method of using a warm top-fermenting yeast. Over time the Alt yeast adjusted to lower temperatures, and the Alt brewers would store or lager the beer after fermentation, leading to a cleaner, crisper beer than is the norm for some other top-fermented beers such as British pale ale.

The Bavarian Reinheitsgebot (beer purity law) of 1516 did not affect brewers of the Rhineland. As such, the brewing traditions in this region developed slightly differently. For example, brewing during the summer was illegal in Bavaria, but the cooler climate of the Rhineland allowed Alt brewers to brew all year long and to experiment with storing fermented beer in cool caves and cellars. The first brewery to use the name Alt was Schumacher which opened in 1838.Alt is a dark, lagered, top-fermented beer that has some of the lean dryness of a lager but with fruity notes.

Well known German Altbier that does not come from Düsseldorf is produced by the Pinkus Müller brewery in Münster, the Diebels brewery in Issum, the Gleumes brewery in Krefeld and the Bolten brewery in Korschenbroich. Venlo, a city in the Netherlands on the German border near Düsseldorf, produced the first Dutch Altbier. Altbier is also brewed in small quantities in Austria, Switzerland and the United States. Some Altbier breweries have a tradition of producing a somewhat stronger version known as Sticke Alt, coming from a local dialect word meaning “secret”. It is generally a seasonal or special occasion brew, and is stronger and sometimes darker than the brewery’s standard output.

Zum Schlüssel has recently colloborated with Creemore Springs, and created a style of Altbier at its brewery located in Ontario, Canada. In order to ensure the company is making an authentic Altbier, Creemore Springs actually sent its brewmaster, Gordon Fuller, and head brewer Bryan Egan to Dusseldorf in February of 2012 to learn about the traditional brewing methods. This has resulted in a collaborative effort between Creemore Springs and the Zum Schlussel brewpub, which provided samples of its house yeast strain for the brew. The ability to draw on the flavour imparted by the traditional yeast strain has the benefit of making the Altbier more than simply an homage to the style. The yeast strains used in Dusseldorf represent hundreds of years of brewing.