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Sourdough is a symbiotic culture of lactobacilli and yeasts used to leaven bread. Sourdough bread has a very distinctive taste, due mainly to the lactic acid produced by the lactobacilli.

Biology and chemistry of sourdough

A sourdough starter is a stable symbiotic culture of yeast and lactobacteria[?], typically Candida milleri[?] for the yeast and Lactobacillus sanfrancisco[?] for the lactobacteria, growing in a paste of flour and water.

A flour water mixture will tend to develop this symbiotic culture after repeated feedings. Fresh, organic, and wholemeal flour raises the probability of initiating this symbiosis. The flour water mixture also can 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.

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. In a typical wheat flour dough the rise is approximately 50% due to the yeast and 50% due to the lactobacteria. A yeast cell produces far more of the carbon dioxide leavening gas than a lactobacteria, but there are many more lactobacteria, a ratio of 100 to 1 being typical.

History of sourdough

Sourdough has been used since ancient times with a variety of grains.

Bread made from 100% rye flour, which is virtually unknown in the United States but 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 gluten - sourdough however, in lowering the pH level of the dough, causes the starch to partially gelatinize[?], enabling it to retain gas bubbles.

External links

  • Sourdough FAQs (http://www.nyx.net/~dgreenw/sourdoughfaqs)
  • Sourdough Success! (http://www.kuro5hin.org/story/2003/4/17/1055/55941) by Rusty Foster, Kuro5hin, April 17, 2003. Article and discussion about making sourdough only from water and flour.

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