Grünkohlessen is an old custom in North Germany and parts of Scandinavia, particularly in the state of Bremen and its surrounding districts. Grünkohl (locally also known as Braunkohl), a form of cabbage, was formerly harvested after the first autumn frost which neutralised its bitter constituents. Today more recent varieties are used that can be harvested - without the need for frost – from September.
The participants in a Kohlfahrt ("cabbage walk") arrange a walk through the countryside to a village pub, usually in mid-winter. Often this walk is linked with cross-country games like Boßeln and the like. As fortification against the frosty weather and in preparation for the hearty meal, an ample supply of alcoholic beverages, such as korn, or for sailors, sherry, is taken in a shopping trolley or handcart, which are handed out as part of the games or at waypoints along the walk (e.g., at crossroads or pylons). At the village pub, the merry walkers are served with Grünkohl and, depending on the region, with [sweet (not to everyone's taste)] baked potatoes or boiled potatoes and Kassler, Bregenwurst, Pinkel or Kohlwurst. In addition there is also much to drink (beer, Korn) allegedly to aid the digestion. In many areas there is also music and dancing after the meal.
The Grünkohlessen reaches its climax in the proclamation of the Kohlkönig ("cabbage king") or the Kohlkönigspaar ("cabbage couple"). Various methods are used to award the royal title. Either the number of portions consumed is added up, the weight of the participants before and after the meal is measured, or the results of the games during the walk are used. The Kohlkönig is singled out as the last to leave the table. This excludes visits to the toilet or dancing breaks. As a visible sign of royalty, chains with the history of the Kohlkönigs of this group or a pig's jaw bone with an appropriate inscription are worn. The king or royal couple have the responsibility of organising the following year's Grünkohlessen.
Source: Wikipedia, "Grünkohlessen", available under the CC-BY-SA License.