- This article is about sourdough bread. For early Alaska settlers sometimes called sourdoughs, see Alaskan sourdough.
Sourdough is a symbiotic culture of lactobacilli and yeasts used to leaven bread. Sourdough bread has a distinctively tangy or sour taste (hence its name), due mainly to the lactic acid and acetic acid produced by the lactobacilli.
Sourdough bread is made by using a small amount (20-25%) of “starter” dough (sometimes known as “the mother sponge”), which contains the yeast culture, and mixing it with new flour and water. Part of this resulting dough is then saved to use as the starter for the next batch. As long as the starter dough is fed flour and water daily, the sourdough mixture can stay in room temperature indefinitely and remain healthy and usable. It is not uncommon for a baker’s starter dough to have years of history, from many hundreds of previous batches. As a result each bakery’s sourdough has a distinct taste. The combination of starter, yeast culture and air temperature, humidity, and elevation also makes each batch of sourdough different.
Biology and chemistry of sourdough
A sourdough starter is a stable symbiotic culture of bacteria and yeast present in a mixture of flour and water. The yeasts Candida milleri or Saccharomyces exiguus usually populate sourdough cultures symbiotically with Lactobacillus sanfranciscensi.[1]. Lactobacillus sanfranciscensis (bacteria) was named for its discovery in San Francisco sourdough starters.
Often a starter will consist of basic items such as: water, bread flour, rye flour and a sourdough starter which can be purchased at certain grocery stores. Once the starter is made water and flour must be added in time increments over a period of days.
A fresh culture begins with a mixture of flour and water. Fresh flour naturally contains a wide variety of yeast and bacteria spores. When wheat flour contacts water, naturally-occurring amylase enzymes break down the starch into complex sugars (saccharose and maltose); maltase converts the sugars into glucose and fructose that yeast can metabolize. The lactobacteria feed mostly on the metabolism products from the yeast. <ref name=”rosada”>Rosada, Didier (1997) Advanced Sourdough. Minneapolis: National Baking Center.</ref> The mixture develops a balanced, symbiotic culture after repeated feedings.
There are several ways to increase the chances of creating a stable culture. Unbleached, unbromated flour contains more microorganisms than more processed flours. Bran-containing (wholemeal) flour provides the greatest variety of organisms and additional minerals, though some cultures use an initial mixture of white flour and rye flour or “seed” the culture using unwashed organic grapes (for the wild yeasts on their skins). Using water from boiled potatoes also increases the leavening power of the bacteria, by providing additional starch. Bakers recommend un-chlorinated water for feeding cultures. Adding a small quantity of diastatic malt provides maltase and simple sugars to support the yeasts initially.<ref name=”reinhart”>Reinhart, Peter (1998) Crust & Crumb: Master formulas for serious bread bakers. Berkeley: Ten Speed Press. ISBN 1-58008-003-0</ref>
The flour-water mixture can also be inoculated from a previously kept culture. The culture is stable due to its ability to prevent colonization by other yeasts and bacteria as a result of its acidity and other anti-bacterial agents. As a result, many sourdough bread varieties tend to be relatively resistant to spoilage and mold.
The yeast and bacteria in the culture will cause a wheat-based dough, whose gluten has been developed sufficiently to retain gas, to leaven or rise. Obtaining a satisfactory rise from sourdough, however, is more difficult than with packaged yeast, because the lactobacteria almost always outnumber the yeasts by a factor of between 100 and 1000, and the acidity of the bacteria inhibit the yeasts’ gas production. The acidic conditions, along with the fact that the bacteria also produce enzymes which break down proteins, result in weaker gluten, and a denser finished product.<ref>McGee, Harold (2004). On Food and Cooking: The Science and Lore of the Kitchen, 544. New York: Scribner. ISBN 0-684-80001-2</ref>
History of sourdough
Sourdough originated in Ancient Egyptian times around 1500 BC.
Bread made from 100% rye flour, which is very popular in the northern half of Europe, is always leavened with sourdough. Baker’s yeast is not useful as a leavening agent for rye bread, as rye does not contain enough gluten; sourdough, however, in lowering the pH level of the dough, causes the starch to partially gel, enabling it to trap gas bubbles. In the southern part of Europe, where baguette and even panettone were originally made with sourdough, it has been replaced by the faster growing yeast.
Sourdough was the main bread made in Northern California during the California Gold Rush, and it remains a part of the culture of San Francisco today. The bread became so common that “sourdough” became a general nickname for the gold prospectors. The nickname remains in “Sourdough Sam”, the mascot of the San Francisco 49ers.
San Francisco sourdough is the most famous sourdough bread made in the US. In contrast to the majority of the country, it has remained in continuous production for nearly 150 years, with some bakeries able to trace their starters back to California’s territorial period. It is a white bread, characterized by a pronounced sourness (not all varieties are as sour as the San Francisco sourdough), so much so that the dominant strain of lactobacillus in sourdough starters was named Lactobacillus sanfranciscensis. Another reason sourdough was popularized in San Francisco is that it is said that the fog (which is abundant in San Francisco) helps to rise sourdough and give it a more distinct “sour” taste. Sourdough also popularized because of its ability to combine well with seafoods and soups such as clam chowder and chili.
Sourdough has not enjoyed the popularity it once had since bread became mass-produced. Manufacturers make up for the lack of yeast and bacteria culture by introducing an artificially-made mix known as bread improver into their dough.
Sourdough breads
- Amish Friendship Bread, which uses a sourdough starter that includes sugar and milk, and also uses baking powder and baking soda.
- Biga, an Italian form of Sourdough
- Pumpernickel, a sourdough bread from the Westphalia region of Germany
External links
- sourdough baking tutorial from eGullet.com
- Sourdough.com.au - A Sourdough Bread Community
- Sourdough FAQs
- Modeling of Growth of Lactobacillus sanfranciscensis and Candida milleri… from Applied and Environmental Microbiology, July 1998, by Gänzle et al., Universität Hohenheim
- sourdough bread first hand
- Sourdough Home - An Exploration of Sourdough
- Carl’s Friends Sourdough Starter free sourdough starter
- SourdoughBreads.com commercial vendor of San Francisco sourdough starter and related items
References
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