In the world of German brewing, Krusen refers to the intense proliferation of bubbles and foam formed during fermentation of a young or green beer. And Aufkrusen (literally to krusen it up), refers to a historic brewing technique in which some green beer is added to a fully-matured lager. This is a very old and very typically German tradition, and today even English-speaking brewers refer to this technique as krausening. Krausening brings the vibrant freshness of young beer to the more refined, austere flavors of a fully-matured lager.Aecht Schlenkerla Krusen is an amber-colored, unfiltered lager beer with beautiful malt flavors and a slight smokiness. It matures for months in the deep rock cellars underneath the Schlenkerla brewery and is krausened with Aecht Schlenkerla Rauchbier just before kegging. Quaffable and with a pleasantly moderate level of alcohol, Aecht Schlenkerla Krusen is an ideal refreshment for the warmer months.