1  The history of sourdough

We will start this book by briefly talking about the long history of sourdough bread from ancient time, and how people used similar process for other food like beer. The discovery of yeast and how, together with machine development, revolutionized bread making. More recently communities formed around sourdough and home baking, trying to relearn lessons from the past.

The story of sourdough bread begins in prehistoric oceans. These oceans were the birthplace of all life on Earth. To better envision the vast history of our planet, lets create a timeline in one year/365 days. On this scale, January 1 signifies Earth’s formation 4.54 billion years ago. Midnight on December 31 is the present. Each day represents roughly 12 million years. This technique simplifies the complexity of time but also renders the extraordinary expanse of our planet’s history into a more graspable timeframe. We humans, are in fact a recent addition to our planet, so young that we made our first appearance on the evening of December 31. It seems that humans managed to arrive just in time to join the celebration at the end of the year.

On March 25, the oceans birthed the first single-celled bacteria. In these waters, another single-celled life form, archaea, also thrived. These organisms inhabit extreme environments, from boiling vents to icy waters.

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Figure 1.1: Timeline of significant events starting from the first day of Earth’s existence, divided into months, and extending to the present day, marked at midnight. This visualization shows the pivotal steps of life and sourdough on earth.

Whoever comes first, bacteria or archaea, remains debated. For three months (or approximately 1.1 billion years), these life forms dominated the oceans. Then, on June 25 in an highly unlikely event, an archaeon consumed a bacterium. Instead of digesting it, they formed a symbiotic relationship. This led to the first nucleated organisms, marking an evolutionary milestone. This event lead to the development of plants, fungi and also ultimately humans.

Life stayed aquatic for another three months. On October 4, bacteria first colonized land. By October 15, the first aquatic fungi appeared. They adapted and, by November 24, had colonized land.

By December 3, yeasts emerged on land. This laid groundwork for bread-making. Jump 140 million years to December 14, and dinosaurs arose. Just a couple of days after their appearance on December 17 the super continent pangea started to rift apart, reshaping the continents into their current form. The dinosaurs reigned until December 29 when they faced extinction. Another 25 million years later, or our timeline’s 2 days after the dinosaur extinction, humans appeared.

A few hours later after the arrival of humans, a more subtle culinary revolution was unfolding. By 12 000 BC, just 5 seconds before our metaphorical midnight, the first sourdough breads were being baked in ancient Jordan. A blink of an eye later, or 4 seconds in our time compression, Pasteur’s groundbreaking work with yeasts set the stage for modern bread-making. From the moment this book began to take shape to your current reading, only milliseconds have ticked by [43].

Now delving deeper into the realm of sourdough, it can likely be traced to aforementioned Ancient Jordan [2]. Looking at the earth’s timeline sourdough bread can be considered a very recent invention.

The exact origins of fermented bread are, however, unknown. One of the most ancient preserved sourdough breads has been excavated in Switzerland [24].


Figure 1.2: An ancient Einkorn flatbread. Note the dense crumb structure.

Another popular story is that a lady in Egypt was making a bread dough close to the Nile river. The lady forgot the dough and at her return a few days later, she noticed that the dough had increased in size and smelled funky. She decided to bake the dough anyway and was rewarded with a much lighter, softer, better tasting bread dough. From that day on she continued to make bread this way [39].

Little did the people back then know that tiny microorganisms were the reason the bread was better. It is not clear when they started using a bit of the dough from the previous day for the next batch of dough. But by doing so, sourdough bread making—as we know it today—was born: Wild yeast in the flour and in the air, with bacteria starting to decompose the flour-water mixture. The yeast makes the dough fluffy, and the bacteria primarily creates acidity. The different microorganisms work in a symbiotic relationship. Humans appreciated the enhanced airy structure and slight acidity of the dough. Furthermore, the shelf life of such bread was extended due to the increased acidity.

Quickly, similar processes were discovered when brewing beer or making wine. A small tiny batch of the previous production would be used for the next production. In this way, humans created modern bread yeasts, wine yeasts, and beer yeasts. Only in 1680, the scientist Anton van Leeuwenhoek first studied yeast microorganisms under a microscope. Over time with each batch, the yeasts and bacteria would become better at consuming whatever they were thrown at. By feeding your sourdough starter, you are selectively breeding microorganisms that are good at eating your flour. With each iteration, your sourdough knows how to better ferment the flour at hand. This is also the reason why more mature sourdough starters sometimes tend to leaven doughs faster [23]. It is crazy if you think about it. People have been using this process despite not knowing what was actually going on for thousands of years! The sourdough in itself is a symbiotic relationship. But the sourdough also adapted to humans and formed a symbiotic relationship with us. For food and water, we are rewarded with delicious bread. In exchange, we shelter and protect the sourdough. Spores from the starter are spread through aerial contamination or insects like fruit flies. This allows the sourdough starter to spread its spores even further all around the world.

Brewers would start to experiment with utilizing the muddy leftovers of the beer fermentation to start making doughs. They would notice that the resulting bread doughs were becoming fluffy and compared to the sourdough process would lack the acidity in the final product. A popular example is shown in a report from 1875. Eben Norton Horsford wrote about the famous Kaiser Semmeln (Emperor’s bread rolls). These are essentially bread rolls made with brewer’s yeast instead of the sourdough leavening agent. As the process is more expensive, bread rolls like these were ultimately consumed by the noble people in Vienna [29].


Figure 1.3: A bread made over the stove without an oven.

Only in 1857, the French microbiologist Louis Pasteur discovered the process of alcoholic fermentation. He would prove that yeast microorganisms are the reason for alcoholic fermentation and not other chemical catalysts. What would then start is what I describe as the 150 lost years of bread making. In 1879 the first machines and centrifuges were developed to centrifuge pure yeast. This yeast would be extracted from batches of sourdough. The pure yeast would prove to be excellent and turbocharged at leavening bread doughs. What would previously take 10 hours to leaven a bread dough could now be done within 1 hour. The process became much more efficient. During World War II the first packaged dry yeast was developed. This would ultimately allow bakeries and home bakers to make bread much faster. Thanks to pure yeast, building bread making machines was possible. Provided you maintain the same temperature, your yeast would always ferment exactly the same way.

As fermentation times sped up, the taste of the final bread would deteriorate. The sprouting process induced by certain enzymes is essential to developing a fluffier texture and better tasting crust. This can’t be indefinitely sped up. Soon bakeries would start to introduce additional enzymes to achieve similar properties to sourdough bread in yeast-based doughs. Sourdough almost completely vanished from the surface of the Earth. Only a handful of true nerds would continue making bread with sourdough.

Suddenly people started to talk more often about celiac disease and the role of gluten. The disease isn’t new; it has first been described in 250 AD [5]. People would note how modern bread has much more gluten compared to ancient bread. The bread in ancient times probably was much flatter. The grains over time have been bred more and more towards containing a higher amount of gluten. Gluten is a protein that gives modern bread its typical soft fluffy crumb structure. The gluten proteins bind together once activated with water. Throughout the course of the fermentation, CO 2 is trapped in this protein matrix. The tiny created chambers expand during the baking process. As the dough gelatinizes while being heated, the structure is fortified. This makes the bread appear soft and fluffy when tasting it. Similar to drinking raw cow’s milk, your immune system might react to the consumed proteins. There is gluten intolerance and celiac disease. When people say they don’t handle gluten well, it’s mostly a gluten intolerance they describe. Some people describe similar issues when consuming too much lactose. If you eat a long-fermented cheese however, most of the lactose has been fermented by the tiny microorganisms. People would investigate and note how sourdough bread can typically be handled better compared to plain, fast-made factory bread. The reason for this is that enzymes take time to work the dough. Gluten is a storage protein of flour. Once sprouting is activated by adding water, the protease enzyme starts to convert the gluten into tinier amino acids that are required for sprouting. Over time you are effectively losing gluten as it’s naturally broken down. Furthermore, traditionally lactic acid bacteria would start to decompose the flour-water mix. Almost everything is recycled in nature. Part of their diet is to consume the proteins in the dough. Modern bread is faster and no longer has lactic acid bacteria. Both factors together mean that you are consuming products with a much higher gluten value compared to ancient times when natural fermentation was used [28].

During the California Gold Rush, French bakers brought the sourdough culture to Northern America. A popular bread became the San Francisco sourdough. It’s characterized by its unique tang (which was previously common for every bread). It however remained more of a niche food. What really expedited the comeback of sourdough was the 2020 COVID-19 pandemic. Flour and yeast became scarce in the supermarkets. While flour returned yeast couldn’t be found. People started to look for alternatives and rediscovered the ancient way of making sourdough bread. Soon many realized that making sourdough bread is more complex than modern yeast-based bread. You need to maintain a sourdough starter and have it in ideal shape to properly ferment your dough. Furthermore, compared to a yeast-based dough, you can’t just punch the dough down and let the fermentation continue. You can overferment your dough, resulting in a sticky dough mess. This complexity led to many bakers looking for help and many thriving communities formed around the topic of homemade bread.

When interviewing Karl de Smedt (owner of the Sourdough Library) he said something that changed my way of thinking about bread: “The future of modern bread is in the past [32].”