West Slavic fermented cereal soups

Kyselo has been a traditional daily food of poor people in the Giant Mountain region for centuries, primarily in the winter.[9][11] It is made from locally accessible, cheap, storable ingredients (the mushrooms are usually used dried) and nutritious ingredients so it provides substantial energy for hard mountain life and work.[12] Historically kyselo was made without eggs. Eggs in early times were produced mainly for sale on the market, not for one's own family, so eggs were only eaten on some holidays.[13] Potatoes became widespread among poor people of Czech lands in the late 18th century, so before that time soups of this type were also made without potatoes.[13]

Usage of sourdough indicates that kyselo has ancient origins, probably in medieval (and prehistoric) fermented cereal porridges.[10][13] The Giant Mountain region is on the Czech–Polish border, and kyselo is a close relative of the Polish sour rye soup.[14][15]

The word kyselo is derived from the word kyselý, which means 'sour' in Czech. The sourdough which kyselo is made from is called "chlebový kvásek" or "chlebový kvas" (not to be confused with the Russian kvass).

Sometimes another sour mushroom-based Czech soup kulajda or its variants are mistakenly called kyselo.[16] The difference is that kulajda and similar soups do not use sourdough but sour cream or milk and vinegar. To reduce this misunderstanding, kyselo is often called Krkonošské kyselo ("Giant Mountain Kyselo").

In Eastern regions of the Czech Republic and in Slovakia there is a soup called kyselica, but it is a variation of sauerkraut soup.

The basis of kyselo is strong broth made from mushrooms and caraway in water. Central European mushroom species such as cep and similar ones are used. The mushrooms are usually used dried in the winter.[12] The broth is thickened by sourdough which should ideally be made from rye flour. Families in the Giant Mountains usually grew their own sourdough for years in special cookware called "kyselák" or "kvasák".[10] The thickened broth is supplemented by onion sautéed in butter, boiled and then roasted potatoes and scrambled eggs and seasoned with salt and vinegar.[9][10][12][14][17][18][19] Due to its ancient origins, kyselo has no fixed recipe, and the preparation is a little different in every family. The recipe is passed on by oral tradition. There are local variants of kyselo in the Giant Mountains: without eggs or with hard-boiled eggs, boiled but not roasted potatoes, with or without cream, etc.

Nowadays one can purchase an industry-made instant powder kyselo base for use in big canteens[20] or liquid fermented cereal [21]

Kyselo is traditionally served hot in a soup plate or bowl.[9] In some restaurants it is served in an edible bread bowl.[8] Sometimes it is garnished with chopped scallion, parsley or other green herbs. The soup is eaten with a tablespoon. The potatoes are often served on a special plate (one for the whole table) and everyone can add any quantity as needed.[19] Usually salt and vinegar are also on the table for personal seasoning preferences.

Kyselo is a very nutritious food so it is often served as a main (and only) course, but in small quantities it could be also served as an entrée.

As a staple food, kyselo plays an important part in local legends and fairy tales, especially in connection to the mythical mountain lord Krakonoš (German: Rübezahl). It is said that he gave sourdough to people and invented kyselo.[22] In the Giant Mountains there is also a peak called the Kotel (Polish: Kocioł, German: Kesselkoppe) which means cauldron. When fog rises from the valley at bottom of Kotel, people say that Krakonoš is cooking the kyselo.[23]

The name kyselo is well-known throughout the Czech Republic because of Večerníček children's television series Krkonošské pohádky (Fairy Tales from the Giant Mountains), in which Anče, one of the main characters, cooks kyselo in almost all of the episodes.[24]