Federweißer, also known as Suser or Sauser in Southwest Germany, Switzerland and South Tyrol, Sturm in Austria, New Wine in the Palatinate, and Bremser in Franconia, is a fermenting grape must. The term includes all stages of fermentation from must to finished wine.
Once yeast has been added, grape must begins to ferment rapidly. The fructose contained in the grapes is broken down into alcohol and carbonic acid (glycolysis). As soon as an alcohol content of four percent has been reached, Federweißer may be sold. It continues to ferment until all the sugar has been broken down and an alcohol content of about ten percent has been reached.
Due to the carbonic acid, Federweißer tastes quite refreshing, not unlike a grape lemonade or a sweet sparkling wine. The yeast particles contained in Federweißer are responsible for its name, which literally means white as a feather. In general, Federweißer is made from white grapes; red grapes are only rarely used. In general, it is made from grapes that lack the potential to produce a wine of high quality.
Due to the rapid fermentation, Federweißer can not be stored for long and should be consumed within a few days of purchase. As carbonic acid is constantly produced, the bottles can not be sealed (they would rupture otherwise) and must be stored in an upright position. In the past, the fermentation could not be decelerated by cooling. Thus, transportation over longer distances was impossible, and Federweißer was only available in wine-producing regions.
Depending on the date of the grape harvest, it is available from early September to late October, and is generally served together with savoury food. The classical combination is Federweißer and Zwiebelkuchen, although Federweißer and chestnuts is also popular.
Federweißer contains yeast, lactic acid bacteria, and a large amount of vitamin B1 and B2. It has a positive influence on digestion.