Explore the life of a sourdough
From starting a sourdough culture through using levain in a final dough, learn what brings artisan bread to life.
By Didier Rosada,

National Baking Center Instructor

Modern Baking's Bread and Rolls Handbook

What began as an accident some 5000 years ago, remains essentially unchanged today in artisan bread baking.  Sourdough bread's legend, according to most historians, began in Egypt around 3000 B.C. or 4000 B.C.  A woman who was preparing the traditional unleavened bread of the time,  accidentally left a piece of dough out i the warm, humid Nile River countryside.  By the time she discovered her mistake, the dough had greatly expanded.  She baked it, and, as a result of this mistake, the sourdough process was discovered.

For a long time , this method of baking remained mysterious to bakers. With the evolution of baking science and microbiology in particular, this natural fermentation process has become more understood.  Whether you use scratch methods, bases or frozen dough, a clear understanding of the science and production steps in the sourdough process is essential to create variety, quality and consistency in your artisan bread line

The sourdough process consists of three parts-starting a culture of microorganisms, cultivating them t increase their quantity, and using the resulting levain to ferment the final dough.  After using the levain, the baker perpetuates the culture by adding more flour and water to maintain its activity.

Flora Provides Life for Sourdough

The first step in the life of the sourdough is the flora, which is provided for the most part, by the flour.  The flora is composed of two main types of microorganisms: Yeast and bacteria.  Because every microorganism needs an environment with favorable condition for reproduction, the type and quantity of each microorganism will be affected by the characteristics of the sourdough, such as hydration, ingredients, temperature and acidity content. 

  •  The yeast in a flora are called wild yeast because they are present in any natural environment.  Most of the yeast-cells are members of the saccharomyces cerevisiae family, the same as commercial yeast but wild yeast's genetic characteristics differ slightly. As general rule, wild yeast are more resistant to acidity.

  • The lactic bacteria in the flora are part of the bacillus family (lactobacillus) or coque family (lactocoque) and are classified into two varieties: homofermentative and heterofermantative (different morphology, different reactions in the dough.)
  • The lactic bacteria in the flora are part of the bacillus family (lactobacillus) or coque family (lactocoque) and are classified into two varieties: homofermentative and heterofermantative (different morphology, different reactions in the dough.) 
  • These microorganisms can be found everywhere:  in the air, the water, on the equipment...even on the baker!  The majority of them, however, are in the flour.  One gram of flour contains about 13,000 cells of wild yeast and about 320 cells of lactic bacteria.

Role of Microorganisms

Yeast transforms simple sugars, such as glucose and fructose, into alcohol (ethanol) and gas (carbon dioxide) during the fermentation process.  Carbon dioxide plays a major role in the development of the dough, an the alcohol contributes to the aroma and ultimately t the flavor of the bread.  Secondary fermentation generated by the yeast produces some organic acids also important to  the flavor of the bread. 

 Lactic bacteria converts certain sugars into organic acids.  lactic acid and acetic acid, the two main types of acid produced, transform into aromas.  Lactic acidity plays a direct role in the flavor of the bread.  Acetic acidity reinforces the flavor provided by other aromas and accentuates the sharp acid flavor of the final product.  

Homofermentative bacteria produce only lactic acidity; heterofermantative bacteria produce lactic acidity, acetic acidity and carbon dioxide.

Start the Culture

No matter which method you use to start a sourdough culture, the principle remains the same.  The initial microorganisms come from the flora naturally contained in the flour.  To start a successful sourdough process. you need to develop this flora and activate it enough t ferment the final dough.  To accomplish this, all necessary environmental conditions must e present.  

To produce and grow in the dough, the microorganisms need food, water and oxygen.  The food is provided by simple sugars naturally contained in the flour or from the enzymatic activity.  Te water is added to the flour, and the oxygen is supplied form the air and naturally incorporated into the dough during mixing.

Using organic flour can increase the chances of starting a successful culture.  Because chemical herbicides and pesticides are not used in organic flours, they are richer in microorganism.  Rye flour is another  good option in a culture because  rye flour by nature contains more wild yeast and bacteria than does wheat flour. Rye flour also is richer in minerals which are another source of nutrients for the flora.  Introducing the minerals will speed up the culture activity.  Malt, which is very rich in simple sugars, also can be added to the culture to increase the nutrients available to feed the microorganisms. 

Chart 1: Feeding schedule to develop a starter culture

(Starter is mature when it rises four times its initial volume)



Level of Rise Amount of

culture from

prior feeding

Flour Water Malt
80 F 0 0 0 600 g* 300 g 3 g
80 F 22 hr. 2 300 g 300 g 150 g 2g
80F 7 hr. 3.2 300 g 300 g 150 g
80F 7 hr. 3.5 300 g 300 g 150 g  
80F 6 hr. 4.2 300 g 300 g 150 g
80F 6 hr. 4.3 300 g 300 g 150 g  
80F 6 hr. 4.1
*1/2 wheat f1our and 1/2 organic rye flour

Begin With Flour and Water

Begin by mixing four and water to start the microorganism's activity.  At this stage, the flora is very diverse, and many different types of microorganisms are present in the culture.  In the beginning, sufficient oxygen in the dough and limited flora create conditions  for aerobic activity favorable to reproduction of the microorganisms.

After several hours, the flora grows, reducing the amount of oxygen available.  The microorganisms in the flora then switch to anaerobic activity.  Fermentation activity, enhanced by a constant, relatively-warm temperature, begins.  After about 22 hours, the culture will rise to twice its original volume.

A starter develops, a natural balance (quantity and quality) of yeast and bacteria occurs.  This balance, or natural selection, is achieved because some microorganisms are more or less resistant to the lack of food, lack of oxygen or acidification of the culture. Yeast and bacteria can coexist because thy are not competing for the same type of nutrients.

Due to this natural selection, the flora of levains produced in different geographic areas can begin with the same types of yeast and bacteria.  Yet they develop different characteristics because of the different environments of the culture preparation.  Other minor population of wild yeast and bacteria, more specific to a particular place or process, will inhabit the flora.  This is why, even if the main types of bacteria are the same, each levain is different, and will produce breads with different characteristics in  appearance and flavor.

To keep the flora alive and active, you must renew its vital conditions (food/sugar from the flour, water and air.)  This process, completed several times during starter development, is called feeding the culture.  To determine when the culture needs to be fed, watch for the point when its surface starts to become concave, or collapsed in the center.

The length of time between two feedings depends on the characteristics of the culture (temperature, activity, hydration and ingredients).  A well-established culture should rise four times its initial volume in 6 to 8 hours of fermentation at room temperature.  When this level of activity is reached, the culture becomes a starter

You also can speed up the development of the culture by using ingredients in addition to flour and water, such as malt, honey, milk powder, yogurt, fresh fruits, grapes, etc.  Adding extra nutrients (simple sugars) assists the beginning of fermentation and hosts a different flora, which creates different characteristics in the dough..

From Starter to Levain

This feeding example (right) involves two feeding per day.  The last feeding (second feeding in this example) is called the levain.  Levain is the natural preferment used to ferment the final dough.  Depending on the fermentation time between the two feedings, the ratio of starter, or first feeding, has to be adapted.  A longer fermentation at room temperature requires less starter, or  first feeding, during the feeding preparation.  A shorter fermentation time will require more starter.

Perpetuating the Culture

There are two possible methods to perpetuate the culture.

  • Remove a piece of final dough just before you incorporate the salt.  This piece of dough becomes the first feeding (flour and water have been added during the final dough incorporation.).  This method has the advantage of eliminating one feeding.  The drawback, however, is the risk of changing the characteristics of the culture.  The final dough ingredients and temperature most likely will be different from those in the levain.

  • Another option is to remove a piece of the starter form the levain just before the levain is incorporated onto the final dough.  This process has the advantage of keeping the starter pure because it will never be in contact with the final dough. However, it requires an extra feeding.

Feeding Example:
Flour 100%
Water 50%
Starter 50%
First Feeding  200%

Ferment 12 hours at room 

temperature (75F to 80F)

Flour 100%
Water 50%
First Feeding 50%
Second Feeding* 200%

Ferment 12 hours at room 

temperature (75F to 80F)and final dough preparation

*This is the levain.

Several factors can change the microbiological activity of the culture during the feeding process, and ultimately affect the characteristics of the bread.

Factors Affecting the Culture

  • Hydration:  A stiff culture will have the tendency to develop more acetic acidity, while liquid levain will increase the production of lactic acidity.
  • Temperature: High temperatures (about 85- 90) favor bacterial activity and production of lactic acidity, but fermentation becomes more difficult to control due to a greater yeast activity.  A 77F temperature seems to optimize fermentation activity, development of the dough and production of aromas.  Low temperatures favor the production of acetic acid and suppress fermentation activity.
  • Flour:  Enzyme activity determines the amount of food available for the microorganisms.  Bran content also plays a role in microbiological activity.  Bran is rich in minerals, which are nutrients for the microorganisms.  Generally, a flour with higher extraction (or ash content) provides better activity and higher acidity production.

  • Salt: A small amount of salt (0.1%) could be beneficial for a culture with high protease activity (dough with an excess of extensibility).  Amounts greater than 0.1% can inhibit activity of some microorganisms.

Maintaining the Culture

To keep the levain in its purest condition, pay strict attention to sanitation.  Tables and mixers must be cleaned during the feeding process and the mixing of the final dough. Scraps of dry dough made with commercial yeast should be carefully removed t avid contaminating the culture.

To keep the final product as consistent as possible, maintain a consistent feeding process. The correct proportion of ingredients, feeding schedule, water temperature, fermentation temperature an fermentation time are key points for a consistent and healthy culture.

Use in Final Dough

The quantity of levain used in the final dough depends on the characteristics of the levain, as well as the  characteristics that you want in the final product.  Also, the amount of sourdough you can incorporate in a formula is limited.  A high amount of levain increases the acidity level (or lowers the PH) of the dough.  This acidity decreases the extensibility of the gluten, making it inclined to tear more easily.

No matter what production methods you use, a fundamental knowledge of the sourdough process can help you troubleshoot problems and improve consistency in your breads.  By understanding this age-old process you can develop an unlimited variety of specialty breads.

Sourdough Batards

This formula will yield 44 loaves scaled at 500g each (1 lb. 1.5 ozs.)

First Feeding
Baker's % Metric Lbs. Ozs.
Flour 100 0.85 kg 1 14
Water 50 0.42 kg 15
Starter 80 0.65 kg 1 7
First Feeding 1.92 kg 4 Lbs. 4Ozs.

Method: Ferment for 8 hours at room temerature(75F - 80F). 

Note that fermentation times can change depending on culture fermentation activity



Baker's % Metric Lbs. Ozs.
Flour 95 2.32 kg 5 1.8
Rye Flour* 5 0.12 kg 4.2
Water 50 1.22 kg 2 11
First Feeding 80 1.92 kg 4 4.6
Levain** 5.58 kg 12 Lbs. 5.6 Ozs.

Method: Ferment for 8 hours at room temperature (75F - 80F).

Again, fermentation time may vary.

*Using a small amount of rye flour in the levain preparation has several small, but significant, effects on the final product.  Because rye flour is higher in minerals, which are essential nutrients for the yeast and bacteria, it helps  to maintain the activity of the levain.  Rye flour contains less protein and lower quality protein than wheat flour.  This helps keep the structure of the levain from becoming too strong.

**The amount of  levain includes the levain needed for the final dough plus the starter used to perpetuate the culture.


Final Dough

Baker's % Metric Lbs. Ozs.
Flour 100 10 kg 22 6.4
Water* 70 7 kg 15 6.9
Salt** 2.66 266 g   9.4
Levain 50 5 kg 11 3.2
Total Dough   22.26 kg 49 Lbs. 9.9 Ozs.

*Amount of water can change depending on the flour absorption.

**Salt is 2% based on the total flour weight (flour involved in the levain plus flour from the final dough.)

Mix*.......................... Improved Mix
First Fermentation...... 3 Hours
Dividing..................... 500  g (1 lb. 1.5 ozs.)
Resting Time.............. 30 - 40 minutes
Shaping...................... Batards
Final Proof................. 5 Hours
Baking**.................... 460F for 45 minutes; open the oven door for the last 10 to15 min. to allow the crust dry.

*Incorporate all the ingredients on first speed for three to four minutes.  Then switch your mixer to second speed, and mix just until the dough starts to get smooth.  Te goal is to achieve a lightly developed gluten structure.

**Baking time and temperature also will vary depending on the type of oven