Sourdough2019-06-24T14:32:31-07:00

Sourdough is a method of breadmaking that requires special fermentation by bacteria and wild yeast to provide a sour, or acidic taste in bread.

Sourdough


What is Sourdough?

Sourdough is a method of breadmaking that requires special fermentation by lactic acid bacteria and wild yeast. It is the oldest method used to leaven dough and make bread. Both an art and a science, this process requires time. However, it produces bread with:

  • Extended shelf-life
  • Superior nutritional profile
  • Higher digestibility
  • Better texture
  • Unique flavors and aromas1,2

Origin

The history of sourdough dates back to the earliest civilizations and when cereal grain was domesticated. Some historians claim that this bread originated in Egypt between 4000 and 3000 BCE.3 Bread has always been closely related to human subsistence. And sourdough bread is the perfect example of  how knowledge, combined with agricultural practices and technological processes, become a cultural heritage that is passed to generations through bread.3

How does it work?

Sourdough is a preferment or starter that consists of only cereal flour and water. Cereals used to make it include:

  • Hard wheat
  • Durum wheat
  • Rye

First, the mixture is allowed to ferment spontaneously for a set time. This takes place naturally occurring microorganisms, both present in flour and surrounding air. These microorganisms are represented by lactic acid bacteria (LAB) and wild yeast. There is no added commercial yeast in sourdough.4

Once the flour and water mixture has been properly developed and fermented, it is considered a tarter of optimum vitality and activity. After this, it is ready to be used in bread production.

To keep the sourdough starter active for daily use, it must be refreshed or fed periodically with added flour and water. This can be done weekly, daily or even more frequently. Starters can be perpetuated through proper feeding.

Microflora

The uniqueness of sourdough microflora is tied to the co-existence and symbiotic interaction of wild yeast and lactic acid bacteria. Cell populations of LAB and yeasts in sourdoughs are generally of the order of 108–109 and 106–107 colony-forming units per gram (CFU/g), respectively. There is generally a a ratio of LAB to yeasts of 100:1.5

The following table summarizes the microorganisms isolated and involved in this type of fermentation.1

Microorganism Genus Species Types Type of fermentation Function in dough and bread
Lactobacillus acidophilus

casei

plantarum

delbrueckii

Lactic acid fermentation

Homofermentative reaction:
Glucose, Fructose, Maltose → Lactic acid (>90% of total products)

  • Sourdough starters (microflora)
  • Acidification and maturation of dough
  • Production of sour flavors
  • Shelf-life extension by lowering pH
  • Improved texture
Lactobacillus sanfranciscensis

brevis

fermentum

Lactic acid fermentation

Heterofermentative reaction:
Glucose, Fructose, Maltose → Lactic acid + Acetic acid + CO2

  • Sourdough starters (microflora)
  • Leavening of dough
  • Production of acetic flavors
Saccharomyces

Torulopsis

Candida

Saccharomyces

exiguus

holmii

milleri

cerevisiae

Alcoholic fermentation

Reaction:
Glucose, Fructose, Maltose → Ethanol + CO2

  • Sourdough starters (wild yeast)
  • Leavening of dough
  • Aroma and flavor

More resistant to acidity compared to commercial yeast. Therefore, better adapted to the sourdough process

Application

Sourdough can be used to make any type of bread, even white pan bread. The following breads are made with this type of process:

  • Altamura bread
  • San Francisco bread
  • Rye bread
  • French bread
  • Wheat bread
  • Panettone

This is the most time-consuming breadmaking system. So, it presents high speed bakeries with several scale-up challenges. Production cycle times, operations scheduling, space and equipment needed for proper implementation are just a few of these challenges.

Carefully dried and active forms of sourdough can be used in commercial bakeries to help bring about the many benefits of this process and bread.

Process parameters

The development of sourdough is influenced by the following factors:

  • Flour type
  • Flour extraction rate
  • Flour nutrients such as damaged starch and natural sugars
  • Water absorption, or flour/water ratio.
  • Fermentation temperature
  • Relative humidity of fermentation environment
  • Fermentation time
  • Amount of starter cultures (CFU/g)
  • Acidity, pH and TTA

Sourdough fermentation can be in the form of a firm dough or a liquid suspension of flour in water. The higher the water content, then the higher the production of lactic acid and the lower the production of acetic acid. It also makes the bacteria and yeast grow faster.

Clean label baking

Extended dough fermentations have been used effectively for improving dough development and enhancing bread shelf life. In this context, fermentation is considered an effective alternative to traditional dough conditioners. So, this provides bakers with the means to produce clean label bakery products.1

References

  1. Hutkins, R.W. “Bread.” Microbiology and Technology of Fermented Foods, 2nd Edition, IFT Press and Wiley Blackwell, John Wiley & Sons, Inc, 2019, pp. 301–342.
  2. Chavan, R.S., and Chavan, S.R. “Sourdough Technology—A Traditional Way for Wholesome Foods: A Review.” Comprehensive Reviews in Food Science and Food Safety, Volume 10, Issue 3, April, 2011, pp. 169–182.
  3. Cappelle, S., et al. “History and Social Aspects of Sourdough.” Handbook on Sourdough Biotechnology, Springer Science+Business Media New York, 2013, pp. 1–3.
  4. Corsetti, A. “Technology of Sourdough Fermentation and Sourdough Applications.” Handbook on Sourdough Biotechnology, Springer Science+Business Media New York, 2013, pp. 85–103.
  5. Quan Liu, S. “Sourdough.” Bakery Products Science and Technology, 2nd Edition, John Wiley & Sons, Inc, 2014, pp. 511–518.

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