Sourdough is a dough for the production of baked goods , which is usually kept in fermentation permanently by lactic acid bacteria and yeasts . The resulting carbon dioxide loosens the dough. The typical types of lactic acid bacteria are Lactobacillus plantarum ( homofermentative ) and Lactobacillus brevis ( heterofermentative ). A typical yeast strain in sourdough is Saccharomyces cerevisiae .
Sourdough is added as a leavening agent to loosen baked goods and makes rye dough bakeable in the first place. Sourdough improves the digestibility , aroma , taste , shelf life and cut of the baked goods. Similarly nutritional properties improved.
Sourdoughs contain a community of lactic acid bacteria and yeast fungi that humans have been using for several thousand years for the production of flat cakes, bread and bread-like foods. The metabolic products of these microorganisms loosen the dough and improve the digestibility, the aroma, the taste and the shelf life of the baked goods. Sourdough is of particular importance when using rye flour. Whilst pure yeast can also be used as a leavening agent for wheat flour, acid must be added when using rye flour so that the bread rises and does not stay flat. The lactic acid bacteria in the sourdough produce them in the form of lactic acid and acetic acid .
While processes and methods for inexpensive and efficient bread preparation were sought in the past, the focus today is on the taste and nutritional properties of baked goods made from sourdough. Whole grain products in particular get an improved "mouthfeel" and a better taste through sourdough, while nutritional-determining substances are retained.
Around 79 AD, Pliny the Elder described the production of sourdough by mixing wheat bran with three-day-old grape must. He was also familiar with methods of spontaneous acidification and the continuation of sourdoughs ( sourdough management ). In the Middle Ages, however, the diverse knowledge about agriculture and bread making was forgotten again. This knowledge was only cultivated at the courts and in monasteries.
In Germany in the 15th and 16th centuries, brewers and schnapps distillers supplied bakers with the first yeast. In France, this technology was controversial for a long time because the population feared a health hazard from this new food. Not until 1670 was the use of brewer's yeast allowed, although it had to be mixed with sourdough beforehand. The first yeast cultivars became known in Europe around 1700. Factory production of yeast was established at the end of the 18th century. Carl von Linde 's cooling machines gave a boost to the development of baker's yeast . The brewers switched from top-fermented to bottom-fermented beer after 1877 . This was only possible through cooling, but there was no longer any useful yeast for the bakeries. The development of special baker's yeast was inevitably promoted. The brewers 'and distillers' yeasts were of poor quality. The Saccharomyces cerevisiae strain was specifically selected and produced because excellent baking results were achieved with this yeast.
Rye sour was first replaced by citric acid around 1900 , but the baking results were not optimal. Around 1920 it was recommended to add acids to rye dough to simplify bread preparation, which based on current knowledge also made sense, because flours at that time had a high enzyme content. At the same time, sourdough starter cultures were developed and offered as “pure breeding sour”. In 1930 the first ready-to-use sauces hit the market. They consisted of spring flour and fermented lactic acid. Dried sourdough was also offered around 1930, but due to the process, it only had a low acid content. In 1970 dry sour was brought onto the market as “sourdough extract rye”.
Since then, numerous other processes and baking agents have been developed and continuously improved in order to optimize and simplify the existing sourdough processes.
Types of sourdough
As a rule, sourdough is made from bread-based cereal flour (made from wheat or rye), but it can either be partially or wholly replaced with other flour-like or flour-like products. Are very widespread in Africa Teff -Brot in Ethiopia and z. B. Laxoox in Somalia .
Wheat sour is a dough made from wheat flour, water, yeasts (mainly Saccharomyces cerevisiae ) and often a small amount of lactic acid bacteria ( Lactobacillus plantarum , Lactobacillus brevis ssp. Lindneri ). Some traditional pastries made with wheat sourdough are ciabatta , panettone or Hermann dough .
Rye sour is a mixture of rye flour , water and lactic acid bacteria ( Lactobacillus plantarum , Lactobacillus fructivorans and Lactobacillus brevis ) and mostly yeast ( Saccharomyces cerevisiae ). Not all rye sourdoughs contain enough yeast for loosening. For this reason, sourdough yeasts (acid-fast and leavening yeasts) are often added.
Sourdough made into dry crumbs with a lot of flour is called Krümelsauer (also Gerstl ) and is used for storage.
- this also includes sourdough concentrates . Such concentrates are often sold under the name baking ferment . They are made by gently drying a sourdough made from wheat flour, yellow seed peas and honey. This sourdough form is well suited for private households, as no time-consuming sourdough production is necessary, but the dough is fermentative after adding water and contains yeasts and lactic acid bacteria and is suitable for making bread from bread grains and non-bread grains.
Effects of sourdough
Taste and aroma
Sourdough breads contain a lot of smells and flavors. More than 300 aromatic substances are known, but only a few determine the aroma and taste. Many of the substances involved are already present in the flour, but give a weak flavor impression. Fermentation and the formation of esters (from ethanol and acids) in the sourdough strongly develop these aromatic substances. Carrying flavor compounds such as methylbutanol and diacetyl increase in concentration, but undesirable flavors are also reduced; so z. B. the grassy flavoring hexanal is broken down in sourdough.
Volume, texture and pores
Sourdough increases the specific volume. The pores of the crumb are finer. In addition, a higher level of moisture and elasticity characterize the sourdough flow, which makes the baked goods more solid. When consumed, the mouthfeel is more pleasant, as all fractions of the flour are broken down better: an effect that is particularly effective with whole grain products. Rye breads can be chewed better by lowering the pH value. When chewing, the unleavened crumb sticks to the teeth, causing an unpleasant mouthfeel; as the pH falls, the elasticity of the crumb increases.
- Wheat dough made from sourdough - especially whole grain wheat dough - binds moisture and ensures better and easier processing thanks to good swelling. This is probably also because the solubility of the pentosans increases. The development of glue is improved and the dough becomes more elastic.
- In contrast to wheat dough, rye dough needs acid to be bakeable. In rye dough, the higher proportion of water-binding pentosans - compared to wheat flour dough - prevents the formation of a gluten structure, which is responsible for crumb formation during the baking process. Instead, swollen pentosans and rye starch accumulate and form the stable crumb after they have jammed (exposure to heat). Without acid, the starch would be broken down by the flour's own amylases, could no longer gelatinize and the bread would remain flat and inedible. At a pH value of 4.1, the acids in the sourdough cause the enzyme activities to cease to a large extent and thus the breakdown of starch.
The staling is complex and not fully understood. The bread loses its aroma and mouthfeel, it becomes harder and more brittle; the starch releases moisture and changes to a crystalline state. The moisture moves from the crumb to the crust, where it escapes. So far it is only certain that the formation of exopolysaccharides, which arise during the fermentation of sourdough by lactic acid bacteria, has a significant influence on this.
Sourdough breads mold more slowly than non-leavened or chemically leavened breads. There are many causes and effects. Leavened breads are less susceptible to:
- Mould. The decreased susceptibility is effected against spoilage by lowering the pH and the formation of caproic acid or phenyl -Milchsäuren. During acidification, antimicrobial metabolic products are also created , which work together with the lowering of the pH value. Undissociated acids penetrate the cell nucleus and destroy the vital transmembrane. Diacetyl , acetaldehyde or hydrogen peroxide are also formed, which also have an antimicrobial effect, but affect the smell and taste of the product.
- " Stringing ". In recent years, the old, almost forgotten, bread disease of pulling threads has become more common again. It only occurs with wheat bread and is prevented by adding sourdough.
Sourdough through spontaneous acidification
This procedure is quite old and safe. It is still used today to pull the so-called Anstellgut as the basis for the sourdough.
Lactic acid bacteria are everywhere. They can be found in flour and water. Sourdough can therefore be made by mixing the same amount of (rye) flour and water and letting it stand for about two days at room temperature. If the dough then smells pleasantly sour, often with a fruity note, one can assume that the lactic acid bacteria have prevailed. However, if the approach smells like rotten eggs, one must assume that putrefactive bacteria have prevailed.
However, the result depends heavily on the condition of the raw materials. The storage of raw materials (temperature, humidity) and pest infestation have a major impact on the number and types of microorganisms. In order for a certain type of bacteria or yeast to develop safely, there must be enough germs of this type. Success and quality depend heavily on chance. It is a cutthroat competition that decides which cultures will develop.
Biology and chemistry of sourdough
Sourdough is a stable symbiotic culture of lactic acid bacteria and yeast in a dough of flour and water. Lactic acid bacteria convert sugars that the yeast cannot break down and, on the other hand, yeast metabolize products of lactic acid fermentation. In general, it can be said that the yeasts produce the gas that causes the dough to rise, and the lactic acid bacteria produce the lactic acid, which is responsible for the sour taste and inhibition of the enzyme. Lactic acid bacteria work anaerobically , i. that is, they can multiply in the absence of oxygen. In 1995, Hammes and Vogel distinguished three different metabolic groups of lactic acid bacteria:
- Obligatory homofermentative lactic acid bacteria: They break down hexoses via the Embden-Meyerhof cycle (glycolysis) into two molecules of lactic acid (C 3 H 6 O 3 ). But they do not form any carbon dioxide (CO 2 ). They cannot tolerate oxygen. Lactobacillus delbrueckii and L. acidophilus are typical representatives.
- Optional heterofermentative lactic acid bacteria: they metabolize hexoses to lactic acid and pentoses to lactic and acetic acid. They tolerate and use oxygen. Examples are Lactobacillus casei and L. plantarum .
- Obligatory heterofermentative lactic acid bacteria: They break down hexoses into lactic acid, acetic acid and CO 2 via the Embden-Meyerhof cycle . They break down pentoses into lactic acid and acetic acid. Typical representatives are Lactobacillus fermentum , L. brevis , L. kefiri , and L. sanfranciscensis . The often - wrongly - held opinion that the acetic acid formed comes from vinegar fermentation is not true.
The lactic acid bacteria break down some of the sugars in the flour into lactic acid , acetic acid and a small amount of carbon dioxide . The yeasts produce carbon dioxide and small amounts of alcohol ( ethanol ). The alcohol is converted into acetic acid by the acetic acid bacteria. Various conditions (fermentation time, mixing ratio, temperature) can influence the proportions of the individual fermentation products and thus the properties (effect) and taste of the sourdough. By controlling the temperature, more acetic acid (24–28 ° C) can be formed in the dough, which means that the bread tastes more acidic. Lactic acid has a milder taste. If more lactic acid is to be formed, the dough must be made at approx. 30 ° C. The finished sourdough has pH values between 3.8 and 4.3. The alcohol formed during fermentation combines in part with acids in the dough to form esters , which contribute to the smell and taste of the baked goods. Another part is converted to acetic acid. The ratio of lactic acid to acetic acid in the dough should be between 3: 1 to 4: 1. If the ratio is shifted towards acetic acid, the taste is usually perceived as too sour.
Starter cultures are the basis of a standardized sourdough. During production, a flour-water mixture is specifically inoculated with certain cultures, from which a sourdough develops. Here, too, any leftover items are saved for the next sourdough. At certain time intervals, the sour is often completely freshly prepared with pure breeding sour, with other producers in turn relying on their own, proven cultures that have been stable for years.
Classification of starter cultures for standard sourdough
- Starter for pure sourdough
- Silo sourdough starter
- Starter for storage, suitable for deep freezing
- Starter for bread fermentation
- Starter for freshening sour
- The strain Lactobacillus sanfranciscensis , which is heterofermentative, has prevailed . In addition to acetic acid , lactic acid , ethanol and carbon dioxide are formed. This also creates peptides , amino acids and sugars , which are the basic substances for the subsequent aroma formation in bread.
- Candida humilis has been used as a sourdough yeast for many years .
Starter cultures are offered for the following types of grain:
- Rye sourdough
- Wheat sourdough
- Rye and wheat sourdough
- Spelled sourdough
- Rice starter
- Baking ferments for rye, wheat and other types of grain
The type of grain is irrelevant for the development of the desired microorganisms. The supply of the necessary nutrients is more important, with dark flours faring significantly better.
The outer layers of the rye and wheat grains contain phytic acid , which promotes the development of the young grain and protects it from predators. Dark flours contain a lot of phytic acid, while the proportion of light flours decreases and is insignificant in the case of extract flour. Phytic acid is considered to be anti-nutritional: it binds minerals (Ca, Mn, Mg, Fe) with protein complexes ( phytates ), which makes absorption in the intestine difficult or less. Basically, phytin in bread is insignificant for the human organism because it is not thermally stable; however, minerals remain bound in it. In the sourdough - due to the low pH value - the cereal's own enzymes break down phytate.
Main article: sourdough management
A guide is the production of a sourdough over one or more stages at different temperatures, whereby an attempt is made to achieve a ratio of microorganisms (yeast and lactic acid bacteria) that corresponds to the desired product.
Stirring from ripe sourdough
If a ripe sourdough is not completely used up, the rest can be replaced as a starter . To this, flour and water are added. Since the formation of acid may no longer be satisfactory, undesirable microorganisms can multiply in the dough. Possible consequences:
- sour vinegar tinge
- bitter bread taste
- moist, inelastic crumb
- Uneven pores
To avoid this, a pure breeding sour should be used regularly as a starting point.
Sourdough defects and their causes
Errors in the amount and maturity of the sourdough can lead to typical bread defects:
|root cause||Mistakes in the dough||Bread failure|
|Young, unripe sourdough
or too little sourdough
|• too little acid
• weak driving force in the dough
|- flat, small bread
- moist, inelastic crumb
- streaks of water
- bland taste
|Old sourdough or
too much sourdough
Acidification of the bread dough • weak yeast growth
• strong growth due to lactic acid bacteria
|- large, uneven pores
- moist, inelastic crumb
- taste is too sour
|Sourdough too cold||- large, uneven pores
- strong formation of cavities in the crumb
- dull taste
|Over-cook||- Flat bread
- coarse pores
|Weakened sourdough or
sourdough with poor fermentation
|- Void between the top crust and crumb
- bland, strange or extremely sour taste
General understanding of sourdough
The consumer associates the term sourdough with a product of high quality and natural origin. Various countries have therefore issued guidelines and product descriptions to protect consumers:
In the German Food Book , guiding principles (§ 15 LFGB) are described about the prevailing public opinion for many foods. These guiding principles were developed and continued by consumers, scientists, business, food monitoring and authorities. But guiding principles are not legal principles. One could call it anticipated expert opinion. Products can deviate from these guidelines and can be placed on the market if they are labeled accordingly.
Definition of 2006 (excerpt):
- "1.11 Sourdough is a dough whose microorganisms (e.g. lactic acid bacteria, yeast) from sourdough or sourdough starters are in an active state or can be reactivated. After adding grain products and water, they are capable of continuous acid formation. Parts of a sourdough are used as a starting material for new sourdoughs. The vital activity of the microorganisms is only terminated by baking or hot extrusion. The acidity increase in the sourdough is solely due to its fermentation. "
Sourdough bread is also defined in the guiding principles:
- "3.1 Sourdough bread is made in such a way that all of the added acid comes from sourdough. Reference is made to number 1.11. References to the use of sourdough are only common if more than two thirds of the acid added comes from sourdough. In the case of farmer's / country bread with a rye content of more than 20%, at least two thirds of the added acid comes from sourdough. "
- Section 2.1.1, Paragraph 2:
“Sourdough is a dough made from ground and peeled products, cutlery and drinking water, possibly with the addition of leftover bread, primarily through lactic fermentation. If a starter culture of acid-forming bacteria and / or sourdough yeast (pure culture, pure culture) is used as the starter, the sourdough is referred to as "pure culture sour (dough)". "
- Section 2.1.1, Paragraph 5:
"Natural sourdough" is only called a sourdough that is made with pitched material obtained by removing the ripe sourdough. If the ripe sourdough is originally a pure sourdough (dough), then the items to be placed must have been removed several times in a row so that the designation "natural sourdough" is permitted. "
In Austria, natural sour is therefore very narrowly defined. Its use is required in the production of country and farmer's bread (Codex chapter B18).
In chap. 16 of the Swiss Food Code defines sourdough (excerpt):
- Sourdough is a fermentation made from rye or wheat flour with an active, buoyant microflora that is brought up in several stages by spontaneous fermentation or by starter cultures (lactobacilli) . […] Depending on the type (rye / wheat) and the degree of grinding, the pH value of a mature sourdough is in the range of 3.2–4.5, the acidity between 10 and 30. The acidity (fully mature) is depending on the type of bread and desired flavor note 15–50%.
On September 13, 1993, Decree No. 93-1074 for the protection of breads: Pain Maison, Pain de Tradition Française and Pain au levain in force. Extracts:
- Art. 3: Bread that is marketed under the name “Pain au Levain” must have been made with a sourdough in accordance with Art. 4 and have a maximum pH of 4.3 and more than 900 ppm acetic acid.
- Type 4: Sourdough is a dough composed of wheat or rye flour, drinking water and possibly salt, which is subject to natural acid-forming fermentation and whose function is to let the dough rise. Sourdough contains acidic microflora or yeasts consisting mainly of lactic acid bacteria. The addition of baker's yeast (Saccharomyces cerevisae), which is intended for use in bread dough, is permitted at 0.2% (based on the total amount of flour). The sourdough can also be dried as long as it contains 1 billion bacteria per gram and 10 million yeasts per gram. After adding water and possibly the addition of baker's yeast (Saccharomyces cerevisae), it must produce sufficient dough growth in accordance with the above conditions. Approved types of microorganisms can also be added to the sourdough.
Sourdough does not play a significant role in Christian religious practice. The hosts for the Eucharist have been made from unleavened wheat dough by the Armenians since ancient times and in the Western Church since the 11th century , but this tradition is not religiously binding. In the Eastern Churches , leavened bread is always used.
Sourdough has a different meaning in the writings of the New Testament than in Judaism: The sourdough is a symbol of a dynamic, the quality of which is determined by that of the impulse.
The most important positive image is the parable of leaven ( Mt 13.33 EU par. Luke 13.20-21 EU ), in which the kingdom of God is described as an event that, like leaven, creates constant and unstoppable change, even if the Appears small at the beginning.
In 1 Cor 5: 6ff EU , Paul writes that the believers should cleanse themselves of the discarded doctrines and ways of life, how to clean a house from the old leaven for Passover so that they can accept the new way of life as unleavened dough:
"So let's not celebrate the feast with the old leaven, not with the leaven of wickedness and wickedness, but with the unleavened bread of honesty and truth!"
- Manual sourdough. Biology, biochemistry, technology. Editor Gottfried Spicher, M. Brandt. 6th edition. Behr, Hamburg 2006, ISBN 3-89947-166-0 .
- Horst Skrobanek: Bakery technology. 3. Edition. Craft and technology, Hamburg 2002, ISBN 3-582-40101-4 .
- Lutz Geißler , Judith Stoletzky: Approximately 750 g of happiness - the little book about the great pleasure of baking your own sourdough bread. Becker Joest Volk Verlag, Hilden 2018, ISBN 978-3-9545-3159-2 .
- Baking with sourdough from the Adler Mühle
- Simone Reich: craftsmanship! How to bake a really good bread , SWR TV - Landesschau Rheinland-Pfalz from October 30, 2018 (YouTube from July 20, 2018)
- W.P. Hammes, RF Vogel: WH Holzapfel, Brian JB Wood (Eds.): The Genera of lactic acid bacteria . Blackie Academic & Professional, London 1995, ISBN 0-7514-0215-X , pp. 19-35 (accessed March 12, 2013).
- Ternes, Täufel, Tunger, Zobel: Food Lexicon . Behr's Verlag, Hamburg 2005, ISBN 3-89947-165-2 .
- Pliny the Elder Ä. Natural history 18, 26
- Josef Loderbauer: The baker's book in learning fields . Verlag Handwerk und Technik, Hamburg 2008, ISBN 978-3-582-40205-9 .
- Adelung: Grammatical-Critical Dictionary of High German Dialect. Vol. 2. Leipzig 1796, pp. 1804-1805. (Krümelsauer, the)
- Klaus J. Lorenz, Karel Kulp: Handbook of dough fermentations . Marcel Dekker, New York 2003, ISBN 0-8247-4264-8 , pp. 23-50 (accessed March 12, 2013).
- Lactic Acid Fermentation in Sourdough
- Hammes and others phylogenetically reassigned Lactobacillus sanfranciscensis to L. Buchneri , Dellaglio and Felis assign it to L. fructivorans . Taxonomy of Lactobacilli and Bifidobacteria (PDF; 428 kB)
- Belitz, Grosch, Schieberle: Textbook of food chemistry. Springer, Berlin / Heidelberg 2007, ISBN 3-540-73201-2 .
- Guidelines on bread (PDF; 42 kB)
- Austrian Food Book, IV. Edition, Chapter / B 18 / Baked Products