SOURDOUGH

          

           Sourdough bread is made by the fermentation of dough using naturally occurring lactobacilli and yeast. Sourdough bread has a mildly sour taste not present in most breads made with baker's yeast, and better inherent keeping qualities than other breads due to the lactic acid produced by the lactobacilli. 

History

           In the Encyclopedia of Food Microbiology, Michael Gaenzle writes: "The origins of bread-making are so ancient that everything said about them must be pure speculation. One of the oldest sourdough breads dates from 3700 BCE and was excavated in Switzerland, but the origin of sourdough fermentation likely relates to the origin of agriculture in the Fertile Crescent several thousand years earlier . Bread production relied on the use of sourdough as a leavening agent for most of human history; the use of baker's yeast as a leavening agent dates back less than 150 years."

           Bread made from 100% rye flour, popular in the northern half of Europe, is usually leavened with sourdough. Baker's yeast is not useful as a leavening agent for rye bread, as rye does not contain enough gluten. The structure of rye bread is based primarily on the starch in the flour, as well as other carbohydrates known as pentosans; however, rye amylase is active at substantially higher temperatures than wheat amylase, causing the structure of the bread to disintegrate as the starches are broken down during cooking. The lowered pH of a sourdough starter, therefore, inactivates the amylases when heat cannot, allowing the carbohydrates in the bread to gel and set properly. In the southern part of Europe, where panettone was originally made with sourdough, sourdough has become less common in recent times; it has been replaced by the faster-growing baker's yeast, sometimes supplemented with longer fermentation rests to allow for some bacterial activity to build flavor. 

            French bakers brought sourdough techniques to Northern California during the California Gold Rush, and it remains a part of the culture of San Francisco today. The nickname remains in "Sourdough Sam", the mascot of the San Francisco 49ers. Sourdough has long been associated with the 1849 gold prospectors, though they were more likely to make bread with commercial yeast or baking soda. The "celebrated" San Francisco sourdough is a white bread characterized by a pronounced sourness, and indeed the strain of Lactobacillus in sourdough starters is named Lactobacillus sanfranciscensis, alongside the sourdough yeast Candida milleri found in the same cultures.

           The sourdough tradition was carried into Alaska and the western Canadian territories during the Klondike Gold Rush of 1898. Conventional leavenings such as yeast and baking soda were much less reliable in the conditions faced by the prospectors. Experienced miners and other settlers frequently carried a pouch of starter either around their neck or on a belt; these were fiercely guarded to keep from freezing. However, freezing does not kill a sourdough starter; excessive heat does. Old hands came to be called "sourdoughs", a term that is still applied to any Alaskan or Klondike old-timer. The significance of the nickname's association with Yukon culture was immortalized in the writings of Robert Service, particularly his collection of "Songs of a Sourdough". 

          In English-speaking countries, where wheat-based breads predominate, sourdough is no longer the standard method for bread leavening. It was gradually replaced, first by the use of barm from beer making, then, after the confirmation of germ theory by Louis Pasteur, by cultured yeasts. Although sourdough bread was superseded in commercial bakeries in the 20th century, it has undergone a revival among artisan bakers.

Preparation

           

Started

          The preparation of sourdough begins with a pre-ferment (the "starter" or "leaven", also known as the "chief", "chef", "head", "mother" or "sponge"), a fermented mixture of flour and water, containing a colony of microorganisms including wild yeast and lactobacilli. The purpose of the starter is to produce a vigorous leaven and to develop the flavour of the bread. In practice there are several kinds of starters, as the ratio of water to flour in the starter (hydration) varies. A starter may be a liquid batter or a stiff dough. 

          Flour naturally contains a variety of yeasts and bacterial spores. When wheat flour comes into contact with water, the naturally occurring enzyme amylase breaks down the starch into the sugars glucose and maltose, which sourdough's natural yeast can metabolize. With sufficient time, temperature, and refreshments with new or fresh dough, the mixture develops a stable culture. This culture will cause a dough to rise if the gluten has been developed sufficiently. The bacteria ferment maltose that the yeast cannot metabolise, and the byproducts are metabolised by the yeast which produces carbon dioxide gas, leavening the dough.

Refreshment of the Started

  

          As it ferments, sometimes for several days, the volume of the starter is increased by periodic additions of flour and water, called "refreshments". As long as this starter culture is fed flour and water regularly it will remain active. The ratio of fermented starter to fresh flour and water is critical in the development and maintenance of a starter. This ratio is called the refreshment ratio. Higher refreshment ratios are associated with greater microbial stability in the sourdough.

Intervals between Refreshment

         

          A stable culture in which L. sanfranciscensis is the dominant bacterium requires a temperature between 25–30 °C (77–86 °F) and refreshments every 24 hours for about two weeks. Refreshment intervals of longer than three days acidify the dough and may change the microbial ecosystem.

          The intervals between refreshments of the starter may be reduced in order to increase the rate of gas production, a process described as "acceleration." In this process, the ratio of yeasts to lactobacilli may be altered. Generally, if once-daily refreshment-intervals have not been reduced to several hours, the percentage amount of starter in the final dough should be reduced to obtain a satisfactory rise during proof.

          Faster starter processes, requiring fewer refreshments, have been devised, sometimes using commercial sourdough starters as inoculants. These starters generally fall into two types. One is made from traditionally maintained and stable starter doughs, often dried, in which the ratios of microorganisms are uncertain. Another is made from microorganisms carefully isolated from Petri dishes, grown into large, homogeneous populations in fermentors, and processed into combined baker's products with numerically defined ratios and known quantities of microorganisms well suited to particular bread styles.

          The conclusion is that every day experiencing physical changes such as color, texture, aroma, volume and mass and than certainly has many cavities and has a sharp acidic aroma and the sourdough feature is good having pores and then moving in the fermentation process, feeding in bacteria it is very important to keep the bacteria alive.