26 Aug 2026
Learn everything you need to know about sourdough in this ultimate guide to everyone's favorite fermented bread. With insights from our Puratos sourdough experts, read on to find out where sourdough originated, what its health benefits are and how to make top quality sourdough products for your business.
The origins of sourdough can be traced back to ancient civilizations, where it was a staple food for many cultures around the world.
One of the earliest records of sourdough dates back to around 3700 BCE in ancient Egypt. Archaeological evidence suggests the Egyptians used wild yeasts and lactic acid bacteria to ferment their dough, resulting in a lighter, more easily digestible bread3. This leavened bread was a significant improvement over the dense and heavy flatbreads that were common during that time.
Given that sourdough bread has been around for thousands of years, it’s even more remarkable that sourdough is likely to make up a significant portion of the future bread market.
Sourdough is a natural leavening agent for bread (also known as a rising agent) that causes the expansion of dough to create a light and airy mixture. It is a fermented ingredient that adds depth of flavor to recipes of all kinds because of the wild yeasts and lactic acid bacteria it contains.
Bakers use this essential living culture, known as a sourdough starter, to ferment dough and develop a wide variety of flavor options, aroma and texture. Traditionally, it is made from flour and water and refreshed regularly to keep its microorganisms active. The yeasts in the starter contribute to fermentation and gas production, while lactic acid bacteria produce organic acids and many of the compounds that influence the taste and aroma of sourdough.
In short, while there are many recipes for sourdough starters, just 3 main ingredients are always needed to make sourdough.
These are:
- Flour
- Water (or other liquids such as juice, milk, yogurt, etc.)
- Two types of microorganisms: lactic acid bacteria and yeast (either airborne and/or present in the raw materials).
What are the different types of sourdough bread?
There is no single type of sourdough bread. Changing the grain, flour, starter culture, hydration and fermentation process can result in very different breads. Some common examples we see include:
- Wheat sourdough bread, which can range from light, mild loaves to more rustic breads with an open crumb.
- Rye sourdough bread, traditionally found in many Northern and Eastern European baking cultures and often characterized by a denser texture and pronounced cereal flavor.
- Wholegrain sourdough bread, made with wholegrain flour and often chosen for a stronger grain taste and higher fibre content.
- Spelt and ancient-grain sourdough, where sourdough fermentation is combined with cereals such as spelt, emmer or other heritage grains.
There can be considerable variation even within these categories. Two wheat sourdough breads, for example, can taste completely different depending on the characteristics.
This diversity is also visible in the Puratos Sourdough Library, where sourdough cultures from different countries and baking traditions are preserved and studied.
Sourdough fermentation starts with a culture of yeasts and lactic acid bacteria: the sourdough starter. These microorganisms use nutrients available in the flour and produce compounds including carbon dioxide and organic acids. Carbon dioxide contributes to dough development and volume, while the acids and other fermentation compounds influence characteristics such as taste, aroma, acidity and texture.
This is why sourdough is often described as naturally fermented bread. Rather than relying solely on commercial baker's yeast for fermentation, a sourdough culture contains a community of yeasts and lactic acid bacteria that work together as a team.
Fermentation is not identical in every sourdough. The flour, hydration, type of starter culture, temperature and time all influence how quickly fermentation progresses and what characteristics develop in the final bread. This allows bakers the opportunity to create a huge variety of flavor profiles using different sourdough starters.
What is bulk fermentation in sourdough?
Bulk fermentation is the first main fermentation of the complete bread dough after the ingredients have been mixed and before the dough is divided and shaped.
It is different from maintaining a sourdough starter. The starter is the culture used to initiate fermentation, while bulk fermentation begins once that starter or sourdough has been incorporated into the final dough.
During bulk fermentation, the dough develops gas, acidity, flavor, and structure. Bakers may also fold the dough during this stage to help strengthen it.
The overall bread-making process can therefore be simplified into 3 distinct stages. Controlling each stage separately makes it easier to achieve consistent volume, texture, acidity, and flavor:
- Starter fermentation: maintaining and refreshing the sourdough culture.
- Bulk fermentation: fermenting the mixed dough before shaping.
- Final fermentation or proofing: allowing the shaped dough to ferment further before baking.
At Puratos, we see a rise in the popularity of bulk fermentation of sourdough. That is when the dough is fermented at lower temperature (around 20°C). That is when the dough is fermented at a lower temperature to slow down microbial activity. Slower fermentation gives bakers more flexibility in their production schedule and influences the development of acidity and aroma. Time and temperature work together: balancing both helps bakers achieve the desired results.
Sourdough R&D manager at Puratos
Bulk fermentation is different from a cold final proof. During bulk fermentation, the dough is fermented before it is divided and shaped, while during a cold proof, the shaped dough is fermented under refrigerated conditions.
How long does sourdough fermentation take?
Sourdough is often associated with slow or long fermentation, but there is no universal number of hours that makes bread and other bakery products "proper" sourdough. Depending on the recipe, the process can include a relatively short bulk fermentation or extend over many hours using cooler temperatures.
This means that a 12-hour, 24-hour, 36-hour or even longer fermentation is not automatically better. However, longer fermentation changes microbial activity, acidity, flavor, and dough characteristics, so temperature, starter quantity, flour, and other process parameters must be adjusted accordingly.
Research also shows that fermentation time and conditions work together to shape the sourdough1. For professional bakers, the goal is therefore not simply to ferment for as long as possible, but to find the right fermentation profile for the desired taste, texture, acidity and production performance.
Sourdough bread is considered more nutritious than other breads because it releases energy slowly and has been shown to be more easily digested than other breads.
Sourdough bread has a low glycaemic index (GI), meaning it releases energy progressively over time instead of causing a sharp increase in blood sugar levels. When energy is released slowly in this way, we tend to feel fuller for longer, allowing us to control our appetite better.
Sourdough fermentation can also help make certain nutrients and minerals in grains more accessible to the body. This makes it an interesting match for wholegrain bread, which is growing in popularity as consumers increasingly look for products that combine nutrition with great taste. Taste Tomorrow research shows that 85% of consumers globally believe grains and seeds add to the healthiness of bread.
How to make a sourdough starter
Though there are many recipes to make sourdough starters of all kinds, to make a simple sourdough starter, all you need is flour and water. Here’s how to do it:
Add 100 grams of water to a jar.
Note: choose a glass Kilner jar, plastic container, or clay container. Avoid using any metallic containers for your sourdough starter.Add 120 grams of flour to the water.
Gently blend the flour and water. The mixture’s texture should resemble applesauce. Keep the sides of the jar clean, as it’s important to avoid leaving any dried pieces of starter on the sides.
Leave your flour and water mixture at room temperature (between 20 and 35 degrees Celsius).
Every 24 hours, repeat steps 1-4: Add 100 grams of water and 120 grams of flour, ensuring to keep the sides of the jar as clean as possible before leaving at room temperature.
Over time, the sourdough will liquefy and bubble due to the increasing acidity. Don't get discouraged if it smells funky or unpleasant after a couple of days; that's when you must persevere.
After five to seven days, depending on the type of flour used, your starter will be bubbly and slightly acidic when tasted.
You can measure the pH level to check your sourdough starter is ready to bake with. Your sourdough starter should have a pH level below 4.2. A pH below 4.2 eliminates any pathogens present in your starter. Once your starter meets these criteria, it is considered mature.
How to maintain a sourdough starter
To maintain your sourdough starter properly, there are a few key steps to follow. First, you need to store it in the fridge, preferably in a sealed container made of plastic or glass. This helps maintain its freshness and prevents any contamination.
To preserve the starter, it is recommended to seal the jars tightly and not open them frequently. This allows the accumulation of CO2, which aids in its preservation. By following these steps, you can keep your starter viable for extended periods, even up to several weeks.
Taking a video or documenting its state is advisable if you plan to leave it longer, such as a few months. If any issues arise, you have a reference point to evaluate its condition and ensure it's still healthy.
How to make sourdough on an industrial scale
The growing popularity of sourdough bread has led many industrial bakers to explore how to capitalize on this trend.
The most significant considerations to think about when mastering a rustic-style sourdough are:
- Achieving the ‘rustic look’
Premium sourdough breads have a rustic look to the crust. This is the result of longer fermentation and higher hydration dough fermented with sourdough. Achieving the optimal ‘waxy’ texture and great-tasting bread requires the right processes and ingredients. - Temperature and time control
The longer you can ferment your sourdough, the more rustic bread characteristics you can create. It’s crucial to ensure you have the correct baking technologies to achieve this on a large scale. - Using improvers
Regardless of how premium your sourdough bread offering will be, improvers are necessary for the industrial process to raise the tolerance of the dough and keep the bread fresh and moist. - Communicating the product
Your packaging is of vital importance. Use it to tell your story and communicate the traditional aspects of the recipe.
A key consideration is to adapt your message to the local culture. Our research shows that different cultures have very different understandings of sourdough. Make sure to understand your audience and tweak your communication accordingly.
