What is Sourdough?
Sourdough is a method of breadmaking that requires special fermentation by lactic acid bacteria and wild yeast. This might result in a sour, or acidic, taste in bread. Sourdough should contain metabolically active lactic acid at 108-109 cfug-1 and yeasts at 106-107 cfug-1, primarily responsible for acidification and leavening action of dough.1
For over 5,000 years, sourdough has been used for all types of bread. But when baker’s yeast made its way into the bakeries some 150 years ago, bakers favored yeast-risen dough over sourdough. This was because yeast fermentation leavens the dough faster and is more consistent.
Recently, a trend towards more tasty traditional and natural recipes has given a rebirth to the sourdough. Sourdough has made a convincing comeback, and its popularity continues to grow as consumers realize the benefits that come with sourdough.
Sourdough is made from flour and water (or other liquids like juice, milk or yogurt). The fermentation occurring in the sourdough results from two types of microorganisms: lactic acid bacteria and wild yeast. These are either airborne and/or present in the raw materials.
Using sourdough (as a leavening agent) gives bread a distinctive taste. Depending on the sourdough you use, the results can be very different. This is due to the variety of microorganisms present around the world, that gives their distinct taste and the flavor to sourdough.
The biggest requirement for sourdough production is time. Otherwise, sourdough production is pretty straightforward. It can be obtained by mixing one part flour with one part water, then letting this mixture rest for about 12 hours. During this time, the microorganisms present in the air, together with the indigenous microorganisms contained in the flour, will start growing2. After 12 hours, one part water and one part flour need to be added again to enable the flora to continue growing. This activity needs to be repeated every day.
Inside sourdough, the microorganisms will feed on the flour to produce alcohol and acids. The lactic and acetic acids are what gives sourdough bread its sour. The alcohol, and other fermentative by-products are what produces its distinctive flavors. After several days of feeding and fermenting, the sourdough is ready to be used. We call this the “mother dough.” When this “mother dough” is added to the bread dough in production, it helps leaven the bread.
During fermentation of sourdough, the rheology of the dough becomes more extensible3. Over fermented sourdough becomes very slack. This is due to the reductive compounds (glutathione) being accumulated. These reductive compounds act like dough-reducing agents to improve pan flow.4
The dosage of sourdough on flour weight can vary from 5% to 50%. The average fermentation time in a bakery will range from 6 to 24 hours.
You can compare sourdough to everything else that is fermented: wine, cheese, yogurt, beer and sausages. In all these products, the microorganisms play the same role like in sourdough: producing acids, esters, alcohol and carbon dioxide (CO2). As can be expected with nature, time changes the flavor and the texture during the fermentation. With aging, products develop more flavor and taste. This also holds true for breadmaking. The longer the process, the deeper the flavor. Therefore, time is the most important ingredient in making great tasting sourdough bread.
Types of Dough
There are as many sourdough as there are the people who make it. Every sourdough is unique due to the flour, microorganism, the temperatures, other ingredients or parameters that are used.
Some bakers have used raisin juice, grated apple, yogurt, honey, and water in which oranges were soaked, etc. In addition, the environment where sourdough is made, will contain particular airborne micro-organisms. These, in combination with different fermentation temperatures, will deliver distinctive flavors to sourdough. These are the reasons why there are so many types of sourdough.
Some sourdough recipes contain more water. Therefore, they are more runny in consistency. Depending on the type of flour that is used, the color will vary from a white to yellow, or creamy to brown.
The bakers who are still using sourdough today, use it mainly in rye bread. This is because rye bread needs a certain level of acidity for it to have good baking properties and sliceability. In wheat bread, the sourdough is mainly used in typical sourdough breads or “Pain au levain,” and this tends to be bread from a typical region or with a typical flavor.
Sourdough can be made with a high acid content. This will result in bread that has a sharp sour, like a San Francisco sourdough bread. On the other hand, a lower acidity would result in a sourdough like Panetone – a bread that has a mild, milky and creamy flavor.
Around the World
Sourdough exists in:
- France as “levain”
- Italy as “lievito naturale”
- Russia as “zakvaska”
- Germany as “sauerteig”
In Spanish, it is called “masa madre”, which means “mother dough.” It refers to a wedding tradition, whereby a daughter is given a piece of sourdough from her mother when she marries away. This is done so as to provide bread for her husband and children. In modern day baking, this refers to the traditional method by which bakers make sourdough by using a small amount of old dough saved from a prior batch.
While we consider sourdough bread to be sour in taste, it is certainly not always the case. In Italy, bakers produce “Lievito Naturale” – which means natural yeast. While in South Africa, they speak of “Soet Suur” (sweet sour), and the Dutch say, “Desem.” The English word probably comes from the German “Sauerteig.” This originates from the rye sourdough that is typically used to make rye breads.
In some countries sourdough is still used because of its functionality. For example, in countries where rye breads are produced, the use of sourdough is a requirement to acidify the dough; this acidification is needed to give the enzymes present in the flour the right environment to do their work.
In France, there is legislation tied to “Pain au levain.” Customers understand and recognize this as a traditional bread with more flavor and nutritional benefits than the standard bread.
In USA, there is the famous “San Francisco sourdough bread.”
Today, we see an increasing trend in bakeries all around the world starting to make their own sourdough.
Sourdough bread can be traced back to the ancient Egyptian civilizations of around 3,000 BC. Sourdough bread is more nutritious than the grain from which it is made, because the sourdough process chemically modifies the nutrients and minerals present in the dough. This makes the sourdough bread more easily digested and its nutrients readily accessible for the body to absorb5. Most importantly, it improves the taste and flavor of bread.
During sourdough fermentation, phenolic compounds and lipids are converted by cereal enzymes. Their conversion improves bread texture and quality.6 The formation of hydroxy fatty acids during growth of L. hammesii in sourdough significantly extends the mold-free shelf life of bread.7
- Salim-Ur-Rehman, Alistair Paterson, and John R. Piggott. “Flavour in Sourdough Breads: A Review.” Trends in Food Science & Technology 17.10 (2006): 557-66.
- Minervini, Fabio, Anna Lattanzi, Maria De Angelis, Giuseppe Celano, and Marco Gobbetti. “House microbiotas as sources of lactic acid bacteria and yeasts in traditional Italian sourdoughs.” Food Microbiology 52 (2015): 66-76.
- Balestra, Federica, Gian Gaetano Pinnavaia, and Santina Romani. “Evaluation of the Effects of Different Fermentation Methods on Dough Characteristics.” Journal of Texture Studies 46.4 (2015): 262-271.
- Jänsch, A., Korakli, M., Vogel, R.F., Gänzle, M.G. “Glutathione reductase from Lactobacillus sanfranciscensis DSM20451: contribution to oxygen tolerance and thiol-exchange reactions in wheat sourdoughs.” Applied and Environmental microbiology 73(2007): 4469-4476.
- Poutanen, Kaisa, Laura Flander, and Kati Katina. “Sourdough and cereal fermentation in a nutritional perspective.” Food Microbiology 26.7 (2009): 693-699.
- Gänzle, Michael G. “Enzymatic and Bacterial Conversions during Sourdough Fermentation.” Food Microbiology 37 (2014): 2-10.
- Black, B. A., E. Zannini, J. M. Curtis, and M. G. Ganzle. “Antifungal Hydroxy Fatty Acids Produced during Sourdough Fermentation: Microbial and Enzymatic Pathways, and Antifungal Activity in Bread.” Applied and Environmental Microbiology 79.6 (2013): 1866-873.