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 [53].

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.

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Figure 1.2: Timeline of significant discoveries and events leading to modern sourdough bread.

The exact origins of fermented bread are, however, unknown. One of the most ancient preserved sourdough breads has been excavated in Switzerland [26].


Figure 1.3: 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 [48].

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 [40].

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 reason1 why more mature sourdough starters sometimes tend to leaven doughs faster [25]. 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.

Evidence suggests early grain grinding in northern Australia around 60 000 BC, notably at the Madjedbebe rock shelter in Arnhem Land [46]. However, a more significant advancement occurred later, as documented by the ancient Greek geographer Strabo in 71 BC. Strabo’s writings described the first water-powered stone mill, known as a gristmill. These mills advanced flour production from a few kilograms up to several metric tons per day [52].

These early mills featured horizontal paddle wheels, eventually termed Norse wheels due to their prevalence in Scandinavia. The paddle wheels connected to a shaft, which, in turn, linked to the central runner stone for grinding. Water flow propelled the paddle wheels, transferring the grinding force to the stationary bed, typically a stone of similar size and shape. This design was straightforward, avoiding the need for gears. However, it had a limitation: the stone’s rotation speed relied on water volume and flow rate, making it most suitable for regions with fast-flowing streams, often found in mountainous areas [41].

In the year 1680, a remarkable scientist by the name of Antonie van Leeuwenhoek introduced a groundbreaking innovation that would forever alter our understanding of the microscopic world and ultimately bread making. Van Leeuwenhoek, a master of lens craftsmanship, possessed an insatiable fascination with realms invisible to the naked eye. His pioneering work birthed the first modern microscope. What set Van Leeuwenhoek apart was the exceptional quality of his lenses, capable of magnifying tiny microorganisms by an astounding factor of 270. Driven by an unrelenting curiosity to unveil the unseen, he embarked on a journey of exploration. He scrutinized flies, examined lice-infested hair, and ultimately turned his gaze toward the tranquil waters of a small lake near Delft.

In this serene aquatic habitat, he made astonishing observations, discovering algae and minuscule, dancing creatures hitherto hidden from human perception. Eager to share his revelatory findings with the scientific community, Van Leeuwenhoek faced skepticism, as it was difficult to fathom that someone had witnessed thousands of diminutive, dancing entities—entities so tiny that they eluded the human eye.

Undeterred by skepticism, he continued his relentless pursuit of the unseen, directing his lens towards a brewer’s beer sludge. In this obscure medium, Van Leeuwenhoek made history by becoming the first human to lay eyes upon bacteria and yeast, unraveling a previously concealed world that would revolutionize our understanding of microbiology [54].

At the same time 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 [32].

As industrialisation began the first steam-powered grain mill was developed by Oliver Evans in 1785. Evans’ design incorporated several innovations, including automated machinery for various milling processes, making it more efficient than traditional water or animal-powered mills. His steam-powered mill marked a significant advancement in industrial technology for bread making [43].


Figure 1.4: A bread made over the stove without an oven.

The biggest advancement of industrial breadmaking happened 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. He continued with his research and was the first person to isolate and grow pure yeast strains. Soon later in 1868 in the Fleischmann brothers Charles and Maximilian were the first to patent pure yeast strains for bread making. The yeasts offered were isolated from batches of sourdough. By 1879 the machinery was built to multiply the yeast in large centrifuges [31]. 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. What ultimately made making large batches of dough possible, was the invention of the electrical kneader. Rufus Eastman, an American inventor, is often credited with an important advancement in mixer technology. In 1885, he received a patent for an electric mixer with a mechanical hand-crank mechanism. This device was not as advanced or as widely adopted as later electric mixers, but it was an early attempt to mechanize mixing and kneading processes in the kitchen using electricity. Eastman’s invention represented an important step in the development of electric mixers, but it wasn’t as sophisticated or popular as later models like the KitchenAid mixer. The KitchenAid mixer, introduced in 1919, is often recognized as one of the first widely successful electric mixers and played a significant role in revolutionizing kitchen appliances for home cooks [44] [33].

During World War II the first packaged dry yeast was developed. This would ultimately allow bakeries and home bakers to make bread much faster and more consistently. Thanks to pure yeast, building industrial bread making machines was now possible. Provided you maintain the same temperature, same flour and yeast strains fermentation became precisely reproducible. This ultimately lead to the development of giga bakeries and flour blenders. The bakeries demanded the same flour from year to year to bake bread in their machines. For this reason, none of the supermarket flour you buy today is single origin. It is always blended to achieve exactly the same product throughout the years.

Modern wheat, specifically the high-yielding and disease-resistant varieties commonly grown today, began to be developed in the mid-20th century. This period is often referred to as the Green Revolution.

One of the key figures in this development was American scientist Norman Borlaug, who is credited with breeding high-yield wheat varieties, particularly dwarf wheat varieties, that were resistant to diseases and could thrive in various environmental conditions. His work, which started in the 1940s and continued through the 1960s, played a crucial role in increasing wheat production worldwide and alleviating food shortages [20].

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 [30].

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 while industrial bread was on the rise. 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 [36].”

1It is crazy if you think about it. People have been using this process despite not knowing what was going on for thousands of years!