The sourdough culture is a natural ferment that has been used for millennia to ferment the cereal and transmute it into bread. It is based on the  natural and spontaneous reproduction of the bacteria and yeasts present in the cereal.  Formerly the bakers used a small portion of the day's bread and increased it by mixing it with water and flour, thus feeding the crop and obtaining enough yeast to ferment the bread the next day. 

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The sourdough is a spontaneous and natural culture of  yeasts and lactic acid bacteria , present in a ratio of 1 to 100. All these microorganisms multiply and feed continuously, so we must  "refresh" the culture  with new batches of flour and water for microorganisms to survive indefinitely. 

The  yeasts  are a very large group of microscopic fungi. In the  sourdough we can find  16 types of predominant yeasts. They feed on sugars and transform them into carbon dioxide (CO2) and ethanol (alcohol). They are responsible for  creating the bubbles  that lift the bread dough. Currently the bakery industry uses only the yeast  Saccharomyces cerevisiae  to ferment bread, so in industrialized breads we lose the work of all the bacteria contained in the sourdough, as well as that of the other 15 yeasts naturally present in the bread. bread. 

The   predominant lactic acid bacteria in sourdough can be of  30  different types . They preferentially produce lactic fermentations (that of cheese), acetic (that of vinegar) and propionic (that of the holes in Emmental cheese) and synthesize volatile compounds, anti-mold substances and anti-spinning agents that give bread a  higher nutritional quality ,  a longer time preservation  and  higher sensory quality  compared to breads made with only  Saccharomyces cerevisiae .

The growing environment

The yeasts and bacteria in the sourdough will grow in one way or another depending on the relationship they have with their environment. The  factors that determine the growth  of some or other microorganisms and therefore, the characteristics of the sourdough and the bread that we make with it are:

• Hydration of  the dough: The more solid doughs (with a lower proportion of water) produce more acetic acid (present in vinegar) and less lactic acid (present in cheese). If they are made with a higher proportion of water (more liquid), the dough will acidify faster. 
• Temperature : Yeasts grow slower but produce more CO2, bacteria grow much faster and add more acidity to the dough. Optimum growth temperatures for Lactobacillus are 30 to 40ºC and those for yeasts are 25 to 27ºC.
• A  pH  between 3.5 and 4.3 gives rise to a well-developed sourdough since, depending on the pH, some bacteria can be affected by their development. The acidification of the sourdough releases the phytase enzymes of the cereals (increasing the availability of nutrients in the bread), increases the amount of gluten molecules (proteins) and at a pH of 4, releases a greater amount of amino acids available in digestion by breaking down cereal proteins.
• The  whole grains  contain a higher amount of ash (minerals of the food that will not burn or evaporate) that favor the growth of bacteria. The bran or shell of the cereal contains about 20 times more ash than the inner or "white" part of it. 

A richer bread

The sourdough improves the bread doughs, especially by reducing the kneading time,  improving its organoleptic and nutritional qualities  and keeping the bread in good condition for longer. 

• The dough made with sourdough  needs less time to knead , since it increases the formation of gluten that retains gas and produces a bread with greater volume.
• The lactic and acetic acid produced by the bacteria enhance the  aroma, the flavor, the texture  and other metabolites also produced by the bacteria  extend the life of the bread .

Health benefits

Breads made with sourdough are more nutritious, reduce allergies and blood sugar spikes and take care of our intestinal flora. Breads made with sourdough are beneficial for health, since:

• They improve sugar and insulin levels  by keeping them stable for longer, since lactic acid slows the digestion of starch, while acetic acid and propionic acid prolong the time during which the stomach empties. 
• Allergies to cereal proteins are  reduced  since these are degraded during fermentation and there is a reduction in the levels of gluten (protein) in bread made with sourdough.
• Increases the nutritional quality  of bread by increasing the enzyme phytase capable of breaking down phytates, which are substances present in the cereal that prevent proper absorption of nutrients, so the body better absorbs phenolic compounds, sterols, vitamins and minerals present in the cereal.
• Increased  fiber intake  in breads made with whole wheat flour lowers the risk of cardiovascular disease, diabetes, hypertension, obesity, and gastrointestinal disorders.
• It acts as a  natural prebiotic  (a substance that stimulates the growth of beneficial bacteria in the colon) by solubilizing fiber, increasing gluten degradation and producing peptides and exopolysaccharides by bacteria.

Industrial bread

Currently, the yeasts that are commonly used in making bread contain only microorganisms of the genus  Saccharomyces cerevisiae .

With this single yeast,  the beneficial effects  of the other 15 yeasts and 30 naturally predominant bacteria in the sourdough are  eliminated , in addition to the effects derived from an  acidification of the dough , since the pH of commercial yeast breads is situated between 5.3 and 5.8.

On the other hand,  "bread made with sourdough" is increasingly being marketed . A  small portion of sourdough is often added to these breads , just enough to commercially label them with that name , leaving all the fermentation work to  Saccharomyces cerevisiae , so these breads will not provide the benefits relative to sourdough breads. with the whole microbial culture of the sourdough. 

From El Campichuelo we recommend that you create your own sourdough, it is easy, fast and when you go on vacation you can refrigerate it, freeze it, leave it at the neighbor's house or take it with you in the form of a ball. If you want to know how we make sourdough bread at home, visit our entry to make  El Pan en Casa . 

Sources :  This information has been extracted from the study by Ana Cristina Cortés Otal on the Impact of the microbiota on the characteristics of breads made with sourdough, published in June 2016 through the University of Zaragoza. You can see the complete work  here .