Sourdough bread is made using "Wild" yeast working together in symbiosis with a bacteria, fermenting the flour to give the bread its sourness. The yeasts types involved are specific to the areas wherein they evolved - such that a yeast caught in Cape Town of South Africa, will perform differently to that found in San Francisco, USA. They will have different levels of activity and different degrees of sourness will result. The bread flavours and textures will be varied from yeast culture to yeast culture also.

The sourdough bread yeast culture is collected once, and may be used continually for many years as it is a live yeast which stays alive as long as there is enough flour available. A portion of the original sourdough culture is always held back to be the basis for the next batch, and this is usually sent into dormancy (for a limited period) by keeping the container in the refrigerator (not the freezer). A sourdough yeast could be used through several generations of bakers.

For centuries bread has been made using this "wild" yeast and fermenting bacteria combination, and then microbiologists were able to breed faster, more active yeasts. However in the process the ability to ferment the flour was lost as the time from mixing to baking was too short to allow the fermenting to occur. Shop-bought bread now is usually flavoured by adding extra ingredients, rather than having flavour inherent in the dough. See the book available at Sourdoughs International for more information on sourdough bread, or to purchase yeasts from around the world. Read the sourdough subsection of my site to see how I go about the sourdough bread making process.