bought this today and found out it originated in ancient Egypt ..
Sourdough is a type of bread produced by a long fermentation of dough using naturally occurring yeasts and lactobacilli. In comparison with breads made quickly with cultivated yeast, it usually has has a mildly sour taste because of the lactic acid produced by the lactobacilli.
The preparation of sourdough begins with a starter made from a mixture of flour and water. As it ferments, sometimes for several days, the starter is refreshed with flour and water, then mixed into the bread dough, which is kneaded and allowed to rise slowly before baking.
Sourdough may have originated in Ancient Egypt around 1500 BC and was probably the first leavened bread. It was the usual form of leavening until the European Middle Ages, when it was replaced by barm from the beer brewing process, and then in the 19th-20th century by baker's yeast. It was historically important in the production of rye-based breads, where yeast does not produce comparable results. It was the main type of bread made in Northern California during the California Gold Rush and it remains a part of the culture of San Francisco today. The sourdough tradition was carried into Alaska and the western Canadian territories during the Klondike Gold Rush. Many breads around the world use similar techniques. Although sourdough bread was superseded in commercial bakeries in the 20th century, it has undergone a revival among artisan bakers.