In our bakery we pride ourselves on baking entirely with a sourdough starter we created some 10 years ago after many failed attempts, long before the COVID-19 Sourdough craze.
Over the past two years in the Bush Order Provisions bakery every loaf of bread that has come out of the oven has been naturally leavened, the term for sourdough bread. We prefer the term naturally leavened, because too many people associate sourdough with a flavour and not as a leavening method. Most grocery store “Sourdough Bread” is not actual sourdough and simply has a vinegar-based additive to add a tang or sour flavour.
Throughout this time, we have also explored the uses of sourdough starter beyond just a leavening agent but also a flavour enhancer.
To understand how to do this, we must first look at what a sourdough starter is. So, bear with us as we bore you with the science of a starter in Part 1 of this series.
A sourdough starter is a culture of microorganisms that are naturally cultivated. The microbes primarily come from the flour used in the mix but can also come from the air, your hands, or the spatula used to mix a starter. With most microbes coming from the flour, it doesn’t matter if your starter is 100 years old or two-weeks old. Every time a starter is fed it essentially replenishes and replaces the previous microbes.
These microbes are harnessed in a sourdough starter when flour and water are mixed. Enzymes in the flour convert the existing starch into simple sugars, which the microbes can feed off and reproduce.
Stick with us here, we’re about to learn something important.
There are two importance microbes within a sourdough starter: yeast and lactic acid bacteria (LAB)
Yeast is where our primary leavening power comes from. The yeast eats these simple sugars and converts them to carbon dioxide and ethanol. In a bakers world, our goal is to not only allow these yeast to feed on sugars to produce CO2, we are also working to develop the perfect gluten structure of the dough that will capture the CO2 allowing the dough and subsequently the bread to proof and rise. Yeast ferments at an ideal rate between 30-35ºC, slowly rising the dough. When thrown into a hot oven, the yeast is supercharged before it dies, and produces CO2 at an exponential rate producing the desired “oven spring” bakers are striving for.
But does yeast provide the well-known sourdough flavour? Not as much as you would think.
A large majority of the flavour comes from Lactic Acid Bacteria (LAB).
LAB are a smaller microbe compared to yeast and can often be 100:1 to yeast in a starter. LAB also digests carbohydrates but instead of producing CO2, produces sour lactic acid (as well as acetic acid). This is the byproduct that is found in dairy products, especially yogurt, plants, and fruit skins.
While LAB does not leaven dough to the same extent as yeast, it is still very important because it regulates the pH of dough. Throughout the fermentation process lactic acid lowers the pH which gives sourdough its characteristic sour flavour. A low pH also helps eliminate undesirable pathogens. Simply put bad bacteria can’t survive in acidic environments, which after baking also helps extend shelf life.
Sidenote, this is often why new sourdough starters fail and go moldy. They don’t yet have enough lactic acid in their environment to keep it healthy.
Where it starts getting interesting is that LAB (mainly acetic acid) can continue fermenting in colder environments, 15-22ºC, but also in a lower temperature range.
So, while yeast goes almost dormant in a refrigerator, LAB continues to consume and digest simple sugars and produce that vinegar like flavour.
Bakers, such as ourselves, will often use “cold proofing” as a method of constructing an ideal production schedule, but also as a flavour enhancer. Now that we know the two main types of bacteria within a sourdough starter, next week we’ll look at how we can manipulate these properties on a very basic level in different products.