Sourdough is bread that is made using naturally occuring wild yeast and lactobacilli (gut-friendly “good” bacteria). These wild yeast and lactobacilli cause the bread to rise without the need to add commercial baker’s yeast and also contribute a characteristic tang to the flavour of the bread. It tends to be more nutritious, flavoursome and easier to digest that bread made using commercial yeast.
Commercial baker’s yeast has only been around since the late 19th century following the pioneering work of Louis Pasteur. Prior to this the majority of bread would have been sourdough in nature. While historically bakers perhaps did not understand the science behind bread making they knew the process to follow and would have typically held back a portion of today’s dough to make tomorrow’s bread, thereby perpetuating a culture of wild yeast and bacteria in the dough which would have leavened their bread. Baking bread often went hand in hand with brewing beer in years gone by and the barm from the brewing process was also used as a raising agent in bread, producing similar results.
People often don’t think of bread making as being a fermentation process, instead using phrases such as ‘leaving the dough to rise’ or ‘proove’. These are actually fermentation processes, during which the yeast and lactobacilli break down starches and sugars in the flour and produce carbon dioxide. The carbon dioxide becomes trapped as gas bubbles in the gluten network causing the dough to rise and producing the characteristic structure & texture of bread.
Bread made with commercial baker’s yeast can be produced from scratch within a few hours. However sourdough bread takes much longer due to the lower concentration of wild yeast present in the dough and is typically made over the course of 3 days. This longer, slower fermentation process in sourdough production confers a number of advantages:
- It allows the development of a fuller, richer flavour in the finished bread
- The wild yeast and lactobacilli begin to break down the structure of gluten making it easier to digest
- The pH of the dough decreases which improves the keeping qualities of the bread
- Enzymes produced by the yeast & lactobacilli break down the phytic acid present in the bran, releasing nutrients and making them easier to digest and absorb in the gut