Fermentation is what causes the dough to rise.


What is Fermentation?

Fermentation is an anaerobic biological process that converts sugars and starches into simpler substances. In baking, it causes yeast and bacteria to convert sugars into carbon dioxide, among other things. This is what causes the dough to rise.

Besides dough, fermentation is also used for the production of:

  • Dairy products, such as cheese, yogurt, kefir, kumis
  • Hydrocolloids, like xanthan gum
  • Organic acids, like citric acid
  • Enzymes
  • Chocolate and flavors
  • Vitamins and antibiotics


The use of fermentation in bread can be traced to the ancient Egyptians in 4000 BCE. In 1854, French chemist and microbiologist Louis Pasteur determined that it was microorganisms in the air that caused food to ferment and spoil.2,3

How it works

In bakery products, fermentation is a complex series of biological reactions that allow dough to leaven. It is carried out by strains of Saccharomyces cerevisiae yeast, wild yeast and lactic acid bacteria (LAB). These microorganisms start by consuming simple sugars in the flour and generated by amylase. This produces CO2 and other compounds, which are responsible for the unique flavor and texture of bread.3

The process starts once yeast/LAB is added to the flour and water, either as individual ingredients or preferments. It continues through early stages of baking where the yeast/LAB is inactivated by heat. The fastest rate occurs during proofing and oven spring stages.

Fermentation stages in bread:

  1. Preferment (optional step): Flour, yeast, water are fermented for a long time. This is essential for the development of unique flavors in some breads and enhancing shelf life.
  2. First fermentation: Mixing prefrements with rest of dough composition. This step may last up to 8 hours in artisan breads.
  3. Second fermentation: Takes place after the dough is first punched.
  4. Proofing: After dough make up and can last from 1 hr to 1 day.
  5. Baking: Loaves are expanded due to yeast and steam generation.


Different microorganisms and fermentation types have different uses in bread dough:3,4

Type Application Commonly Used Microorganisms
Alcoholic fermentation / yeast

Simple sugar → Ethanol + CO2

  • Multipurpose (breadmaking, brewing, winemaking)
  • High-sugar dough formulations (osmotolerant yeast)
  • Leavening, flavor enhancement
  • Sourdough starters (wild yeast)
  • Saccharomyces
  • Candida
  • Torulopsis
Lactic fermentation / lactic acid...

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