Karl de Smedt (Sourdough Librarian), Head of the Sourdough Institute, Puratos, contributed to this article
Sourdough makes one of the most powerful ingredients in a bakery. It can tell a story about tradition and creative, personal interpretations. Unique sourdough notes can define a bakery. Thoughtful attention and gentle care help sourdoughs thrive and continue to offer the same aroma and taste that made them loved in the first place.
What should sourdough feel like? The answers are as diverse as the places they come from. They have a cereal taste in Central Europe, while in Southern Europe they are often fruitier. In Northern Europe, sourdough is described as more acidic, according to the community of bakers showcasing their one-of-a-kind creations in the Quest for Sourdough community.
Lately, sourdoughs with tangy, sour notes are increasingly in demand – primarily because people tend to think sourdough should be sour. The perception of what sourdough should taste like is changing, as consumer understanding broadens, regarding the value of sourdough in baked goods like brownies and croissants. Within Puratos’s own customer base, there’s a shift towards more subtle cereal tastes with creamy or fruity notes.
It all starts with the starter
To achieve a flavor profile that has the power to drive a brand, the sourdough starter must grow – carefully, intentionally and gently. The conditions must be diligently met and adapted to the ingredients used as well as the desired results. Sourdough is simple to make, but experience and knowledge are required to maintain and master it.
There’s no exact right temperature to grow a starter, for instance – it needs to be between 20°C and 35°C. Varying the temperature, level of hydration, or the time between feedings can make a big impact on the taste, texture and look of the final products. Changing feeding times result in various fermentation power, acidity, complexity, digestibility and texture. The number of hours between feedings will have an impact on all these properties. For instance, feeding sourdough every four to six hours gives it a low acidity and higher fermentation power. If it has been fasting for more than eight hours, the sourdough’s lactic acid bacteria grow exponentially and start to outnumber the yeasts, causing a loss in fermentation power and increasing the sourness.
Fermentation power can be boosted by using a fresh starter that has only been fed for between four and six hours. Another simple way to gain fermentation power is to add some bakers’ yeast to the final recipe. However, it should be noted that, although fermentation power increases, it does so at the cost of the complexity of the flavor, which is diminished.
Between feedings, sourdough should be kept at the right temperature: in the fridge if it will not be used for baking over the coming days or weeks, or between 20°C and 37°C if it needs to mature, in preparation for the next bake.
Mixing should also be done with care, for oxygen to always be present, so that microorganisms do not switch between aerobic and anaerobic phases too often, which can disturb fermentation. Puratos recommends stirring liquid sourdoughs frequently to avoid the formation of hooch, a liquid that forms at the surface of the starter when it has consumed all its food.
The quest for sourdough
Puratos established the Quest for Sourdough as a global community dedicated to the art and science of sourdough. Its members can register their sourdoughs, have them analyzed, profiled and compared with sourdoughs from other countries and culinary backgrounds. They can preserve their recipes and discover new ones. Sourdough starters with a completed sourdough profile are eligible to be included in Puratos’ Sourdough Library.
Challenges and opportunities
Sometimes, sourdough might not rise or might stop rising. While the reasons behind this may vary, the phenomenon is commonly caused by having too few yeast cells per gram to be able to sustain fermentation. Over time, the ratio of yeast cells changes compared to lactic acid bacteria, according to the feeding regime and usage rate of the sourdough. This makes the sourdough start to acidify faster and faster. To get out of this vicious cycle, bathing the sourdough helps get rid of excess organic acids – allowing yeast levels to increase.
It’s all about finding a balance between yeast and lactic acid bacteria; more yeast means a better rise. This process requires measurements, knowledge, skills and devotion.
Sourdough harbors a complex consortium of microorganisms, including dominant, subdominant and satellite ones. They all play a vital role, so maintaining this diversity is one of the biggest challenges of making sourdough.
At Puratos’s Sourdough Library, each sourdough is kept in an airtight mason jar, in the fridge at 4°C. “Every two months we revive the starter by feeding it three times, leaving six hours in between each feeding session, preferably at a temperature of 35°C, so that the microorganisms use their energy for propagation instead of fermentation or acidification. This increases microorganism numbers over the next two months of hibernation,” explains Karl de Smedt. Storing sourdough in a box or freezer is not recommended, as its unique microorganism diversity will be lost.
In case the flavor notes of the sourdough change over time, samples of the original strain can be reintroduced to ensure they are preserved. Puratos regularly sends samples from the stored sourdoughs to their owners, in perfect condition. A change in flavor notes usually relates to a loss or change in biodiversity, often caused by an increase in organic acids. “It’s important to know the biodiversity of your sourdough so you can understand how it changes over time. This can be done in two ways; by using culture-dependent identification or by extracting the DNA from a sourdough sample to identify its microbiota. By isolating the dominant strains and preserving them in a freezer at 80°C in the Sourdough Library, we can later reintroduce these into a sourdough to ensure they’re not lost over time,” de Smedt highlights.
Microbe ecosystem science
A few months ago, a sourdough microbiota test tool was launched by LabID, which is a start-up company and partner of the Sourdough Institute. LabID supports the admission process for entering sourdoughs into the Sourdough Library, by testing small samples. The owners of the sourdough receive a report on the yeasts and lactic acid bacteria present, which can help them better understand the sourdough’s behavior, uniqueness and performance. Testing every three to four months is ideal for quality control, so its performance can be optimized over time, the specialist recommends. “Making sourdough is both an art and a science!”
Sourdough goals
Thanks to their uniqueness, sourdoughs can reach celebrity status. For example, the sourdough from the Poilâne Bakery in Paris is iconic, de Smedt illustrates. It is made from a starter containing stone-ground wheat flour before being baked in a wood-fired oven. It is used to create its famed miche bread: a large, round sourdough loaf known for its dense, chewy crumb, thick crust and distinctive tangy flavor.
The famous Tartine sourdough starter is also a notable entry into the ‘sourdough royalty’ list, owned by Chad Robertson from San Francisco and copied by passionate bakers across the world. “I find this one slightly sour, with lots of complexity thanks to the nutty, fruity and cereal notes. Many of Chad’s customers see it as a throwback to the original San Francisco sourdoughs from the mid-20th century,” the specialist shares.
In Italy, we find Bauli, the largest producer of panettone and pandoro in the country, with not only a world-famous sourdough, but also an interesting story behind it: “Named Futura, it was saved from a factory fire in 1996 by the workers. This sourdough dates back to 1922, originating from a small pastry shop in Verona. Today it is used in every new Bauli product development,” he adds.
In Japan, another memorable, unique sourdough is based on cooked rice; while in Mexico, a variety is fed with beer, eggs and lime.
“As the sourdough librarian, I’m lucky to have the unique opportunity to discover such diverse offerings, to help preserve and document them,” de Smedt highlights.
Their use can further extend the breadth of trademark tastes. Sourdough offers immense potential in exciting experimental developments, for the added depth of flavor. From pastries and crackers to pizza dough, waffles and pancakes, or bagels – anything can be reimagined with a new twist. Even though its name suggests otherwise, sourdough can also be a special companion in sweet goods, for an added richness of texture and taste complexity. As long as the desired flavor has been found, and its formula to thrive perfected, the sourdough is the limit, to bold and truly unique creations!
