Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Sourdough Starter- -Background (Source: On Food and Cooking - The Science and Lore of the Kitchen, Harold McGee, p.313.) Sourness in bread was long considered a serious defect, usually the result of poor yeast or letting the fermentation stage go on too long. In poorer areas of northern Europe, where rye bread was the rule, sourness was more acceptable. The term sourdough brings to mind the hard-bitten pioneer whose sharing of the bread starter was a true act of friendship and a lifesaver for many. It also brings to mind the sourdough bread made famous by the gold miners in California and Alaska. They did not have access to fresh supplies of yeast and had to revert to the ancient method of using a piece of leftover dough to start each new fermentation. Eventually, the mother dough or starter would come to be dominated by the microflora characteristics of the local area: contamination by airborne spores would dilute the initial yeast population. Breads with different mothers would have slightly different compositions. This may be why it is reputedly difficult to keep sourdough starters from deteriorating, or changing in microbial content, when they are brought to other parts of the country. Chicago's atmosphere is just not the same as San Francisco's. The predominant yeast in sourdough is not the usual baker's yeast, Saccharomyces cerevisiae but rather Saccharomyces exigus (exigus means small or scanty; cerevisias means "of beer") which thrives in very acidic environments and cannot metabolize maltose (a form of sugar) at all. The acid responsible for the sour taste-about 75% is lactic acid, the rest acetic-is produced by a group of bacteria that has an absolute requirement for maltose and so would be unlikely to grow in a dough populated by baker's yeast. This results in the unique flavor of San Francisco sourdough. Starters that have maintained for decades appear to be very resistant to contamination, and it is thought that some sort of antibiotic action, analogous to that of the Penicillium molds in cheese, may be involved. Sourdough made with baker's yeast has a different flavor but is much easier for the average homemaker to make. The following recipe for a sourdough starter uses such a yeast, and is the one used for the lab experience the students will use.