Sourdough and sour cultures have been used as part of food manufacturing since Ancient Egyptian times. Sourdough was used to give bread flavor and add volume to the loaves being baked. Modern research also suggests that sourdough could also remove mycotoxins from affected wheat.
By Nathan Giles, Senior Bakery Technologist, Campden BRI
Modern day fermentation for bread is achieved by bakery yeast otherwise known as Saccharomyces cerevisiae. Yeast is a single celled organism with a semi-permeable membrane which allows nutrients into the cell which are then turned into carbon dioxide and alcohol. Sourdough however uses bacterial fermentation rather than yeast fermentation, with the dominant strains of bacteria being Lactobacilli. Sourdough fermentation produces a greater amount of lactic acid (between 4 and 10g/kg) and acetic acid (between 0.5 and 2g/kg) than that of fermentation by baker’s yeast (0.1g/kg both lactic and acetic acid). This creates an acidic flavor to the bread and helps with shelf life.
The traditional method for creating a sourdough starter is achieved by mixing together equal quantities of flour and water. The mixture is then left to open to the bakery environment in order to allow the mixture to start the fermentation process. At low temperatures (20-25°C), the lactic acid bacteria grow faster than the yeast and this is what helps to give the sourdough the acidic properties (Gelinas, 2006). To be able to achieve a balanced stable starter, it must be refreshed with flour and water in equal parts. Feeding the culture with flour and water replenishes any nutrients which have been used by bacteria in the process of establishing a colony. A stable balanced culture can be achieved in approximately five days.
Types of Sourdough
Sourdough can be categorized into three types:
Type I: These sourdoughs are produced using traditional techniques and are refreshed daily to keep the micro-organisms in an active state.
Type II: These are sourdoughs which are often used as dough-souring supplements during bread preparation. They are semi-fluid and the silo preparation is characterized by long fermentation periods (2-5 days) with a temperature sometimes greater than 30°C to speed up the process.
Type III: These sourdoughs are dried preparations containing lactic acid bacteria which are resistant to the drying process.
Types II and III require the addition of baker’s yeast (S. cerevisiae) as a leavening agent as these are usually added to the dough to increase shelf life of the product and to add a depth of flavor or texture.
When a product is fermented, the yeast or the sourdough are the biological leavening agents. When yeast ferments, it produces carbon dioxide which enters the pre-existing bubbles in the dough created during the mixing process. Yeast does not create new bubbles in a dough system; therefore, air must be incorporated during the mixing to provide pre-existing bubbles Wieser (2003). The gas cells in the dough become larger as more gas is produced and growth of gas cells changes from slow to rapid after around 25 minutes of fermentation.
Source: World Bakers