Yeast starters contain microorganisms that produce the characteristic flavor of bread.
Yeast starter is, it seems, the starter product used in the production of sourdough bread. While it can be made in many different ways, a starter can be created simply by combining flour and water that ferments and grows bacteria. The microorganisms within the starter end up producing the aroma and sour taste that sourdough bread is named for. The Sourdough starter is essentially self-replicating; As long as it is “powered”, the starter will continue to develop and remain usable, which means some starters may be decades or even centuries old.
Many bakeries have a decades-old sourdough starter.
The basic purpose of the sourdough starter is the development of two microorganisms: a bacteria called lactobacillus and yeast, which is technically a fungus. Since they are microorganisms, they are alive and need to be “fed” to allow them to develop and thrive. This is done by combining water and flour. Any type of flour can work, including wheat, rye, and rice flours. There are already various microorganisms present in the flour itself, including yeast and many different types of bacteria.
Basically what happens in the initial creation of yeast dough starter is that the flour and water are combined and left at room temperature to create an environment in which the yeast and lactobacilli can thrive. Lactobacilli are usually introduced to the mix as bacteria already present in the flour or from the environment. This initial mix is then “fed” additional amounts of flour and water over several days to allow yeast and lactobacilli to multiply, creating an inhospitable environment for other types of bacteria that can be harmful.
As the sourdough starter continues to develop, it creates a potent mix of these two microorganisms. Yeast and lactobacilli create the aroma and flavor of yeast dough, which is often described as pungent or sour. After several days to a week after the starter has been fed and developed, it is usually ready to be used in creating sourdough bread by combining the starter with other ingredients.
One of the advantages of using sour yeast, aside from the characteristic sourdough flavor, is that it can continue to thrive and be used for years. Only part of the starter is used to make bread, and the rest of the starter can be “fed” flour and water and refrigerated to prolong its life. There are many bakeries and organizations that have a yeast dough starter that has been around for decades, some even over a century. The development of an inlet is also influenced by local conditions, including air quality and humidity, which means that inlets in different parts of the world, such as San Francisco, have a different flavor.