Sour cereal soup

A sour cereal soup is a Slavic traditional soup made with various types of cereals such as rye, wheat and oats, which are fermented to create a sourdough-like soup base and stirred into a pot of stock which may or may not contain meat such as boiled sausage and bacon, along with other ingredients such as hard-boiled eggs, potatoes and dried mushrooms.

The most notable, żur (also called żurek, zalewajka, keselica or barszcz biały ), is considered a part of the national cuisines of Poland. Made with soured rye flour (sourdough starter), sometimes also with soured oatmeal, bread or wheat, it has a characteristic slightly sour, thick and tangy taste, and is served hot. Polish żur is the #2 best-rated soup in the world according to world-famous TasteAtlas ranking in 2023.

Sour cereal soup can be also found in Lithuanian, Ukrainian or Belorussian cuisine (as žur, kisjalica or kiselycia), a reminiscence of all these countries current territory being once in Commonwealth of Two Nations. Though it is also prepared in the mountainous regions of Bohemia in the Czech Republic, where it is known as kyselo.

Poland
Żur (żur, diminutive: żurek) is a soup made of soured rye flour (akin to sourdough) and meat (usually boiled pork sausage or pieces of smoked sausage, bacon or pork ribs).

The recipe varies regionally. In Poland it is sometimes served in an edible bowl made of bread or with boiled potatoes. In Silesia, a type of sour rye soup known as żur śląski is served in a bowl, poured over mashed potatoes. In the Podlasie region and also elsewhere in Poland, it is common to eat żurek with halved hard-boiled eggs. In Polish Subcarpathia, there is a traditional variety made of fermented oatmeal (żur owsiany or kisełycia). In Poland żurek is traditionally eaten at Easter, but is also popular during other parts of the year. It is sometimes flavored with bits of sausage, usually eaten with bread or buns.

Another similar soup, sometimes identified as identical with żur – but usually differentiated by its preparation with soured wheat flour rather than rye, is known as barszcz biały (lit. 'white barszcz'). According to some regional traditions, żur is the lenten variation containing no meat and served with additions such as hard-boiled eggs and boiled potatoes, while barszcz biały is a variant with meat such as sausage and bacon.

Following ingredients may be used:
 * cured bones
 * pork ribs
 * white sausage
 * pork belly
 * onion
 * potatoes
 * carrots
 * celery root
 * parsley
 * marjoram
 * bay leaves
 * allspice
 * lovage
 * caraway seed
 * garlic
 * dried mushrooms
 * cream
 * horseradish
 * hard-boiled eggs
 * rye wholemeal bread croutons

Belarus
In Belarus, žur (жур) or kisjalica (кісяліца) is a soup made of fermented oatmeal or rye. Žur may also denote a thicker porridge, a type of kissel made of fermented oatmeal, which is known since the times of Kievan Rus'.

Czech Republic
Kyselo (kyselo, krkonošské kyselo; Kübelsauer ) is a soup based on rye sourdough and mushrooms. It is a traditional Czech cuisine from poor folk food originating in the Northern Bohemia highland region of the Giant Mountains. It is very substantial and it contains an abundance of proteins, B vitamins, dietary fiber and other important nutrients.

Origin
Kyselo has been a traditional daily food of poor people in the Giant Mountain region for centuries, primarily in the winter. 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. 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. 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.

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

Etymology
The word kyselo is derived from the Slavic word ( Polish, Słowak, Czech) „kisić” „to make sour”, 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. 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.

Ingredients and preparation
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. 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". The thickened broth is supplemented by onion sautéed in butter, boiled and then roasted potatoes and scrambled eggs and seasoned with salt and vinegar. 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 or liquid fermented cereal

Serving
Kyselo is traditionally served hot in a soup plate or bowl. In some restaurants it is served in an edible bread bowl. 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. 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.

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

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.

Similar dishes
Eastern European cuisines also have variations of soups based on soured flour or other modes of fermentation. Examples are Russian okroshka made with kvass, Romanian borș made of fermented wheat or barley bran along with ciorbă, and Finnish hapanvelli soup is made with pea and sour dough. A more distant relative is Japanese miso soup, which also uses a fermented basic ingredient – miso paste.