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Fermentation - Part One

22 April 2021

Cooks are a bit like scientists, but instead of small test tubes, they use bowls and spoons for their experiments: they experiment, they mix, they dose ingredients to give life to extraordinary creations. This is exactly what we are going to talk about today, a chemical process that is useful for the formation of our favourite dishes: pizza, bread, brioches and other leavened, sweet and savoury products.

Fermentation in cooking is a biological process by which microorganisms such as bacteria, yeasts and moulds transform the sugars and starches in food into alcohol, carbon dioxide and organic acids. This process is the basis for the preparation of many leavened products, both sweet and savoury, such as bread, pizza, brioches, panettone and doves.

But what are the benefits of fermentation? What are the hidden secrets behind this process? Let's start exploring the world of fermentation now! 


Fermentation not only enables good food preservation by preventing the growth of harmful microorganisms, but also makes food more digestible and enriches the intestinal flora with beneficial microorganisms, contributing to the wellbeing of the immune system.

During fermentation, the gluten proteins (gliadins and glutenins) continue to swell as they absorb CO2 generated by the saccharomyces, which stretch and bind together making the dough spongy. During this process, proteolytic enzymes help to make the dough more malleable. Another important action of fermentation is the increase in temperature of the dough, which is due to the breakdown of the sugars in the yeast: this reaction is called an exothermic reaction, i.e. it generates heat. The exothermic reaction occurs towards the end of fermentation, when the dough has a 2-3% drop in weight due to the transformation of the sugars into volatile substances (carbon dioxide and ethyl alcohol) and the evaporation of water.

There are different types of fermentation used in cooking:

  • Alcoholic fermentation: this is the basis for the production of beer, wine and also bread. In this fermentation, oxygen is absent and the action of yeasts is essential.
  • Lactic fermentation: used for the production of yoghurt, kefir and some cheeses, where carbohydrates are converted into lactic acid.
  • Acetic fermentation: occurs through the action of acetic bacteria that transform ethanol into acetic acid, taking advantage of the presence of oxygen. This process is more of an oxidation than a true fermentation.

In the preparation of leavened goods, fermentation plays a crucial role. The yeast, which can be brewer's yeast or natural yeast (such as sourdough), acts on the sugars in the dough, producing carbon dioxide and alcohol.

In order to achieve good fermentation, it is necessary to create an environment favourable only to the desired microorganisms, which may be more active in foods rich in sugars. In addition, bacterial cultures, starters or mothers that can be purchased online or in pharmacies can be used to ensure more consistent results.


Fermentation not only improves the organoleptic characteristics of food, but also makes it more digestible and enriches its nutritional value:

  1. It improves digestion. Fermentation pre-digests food, making it more easily assimilated by the body.
  2. Strengthens the immune system. Fermented foods are rich in probiotics that help strengthen the body's natural defences.
  3. Absorption of nutrients. Fermentation helps to better absorb vitamins, especially vitamin B, which is essential for various body processes such as digestion and liver and brain function.

4. Benefits for the heart and longevity. Regular consumption of fermented foods can reduce the risk of cardiovascular disease and contribute to a longer life.
5. Aid in weight loss. Fermented foods can positively influence fat metabolism and help reduce the accumulation of abdominal fat.
6. Increased vitamin and enzyme content. During fermentation, beneficial enzymes are generated and the content of vitamins, especially B vitamins and vitamin C, is increased.
7. Increased antioxidants. Fermentation can increase the presence of antioxidants in food.

8. Removal of harmful bacteria. The fermentation process can eliminate any harmful bacteria and toxic substances in food.
9. Food preservation. Fermentation is a natural method of preservation that inhibits the growth of pathogenic microorganisms.
10. Development of new flavours. Fermentation can enhance the organoleptic aspect of food, creating new and pleasant flavours.

Fermentation is a process that not only extends the shelf life of food, but also provides significant health benefits by improving digestibility, nutritional profile and contributing to the well-being of the immune and digestive systems.


Thealcoholic fermentation in yeast is a fundamental biological process that occurs through the action of microorganisms such as yeasts, particularly theSaccharomycescerevisiae, which transform the sugars in the dough into ethyl alcohol (ethanol) and carbon dioxide (CO2).

This process takes place in the absence of oxygen (anaerobiosis) and consists of two main steps:

  1. Scission of sugars. Complex sugars in the dough, such as sucrose, are broken down into simpler sugars (glucose and fructose) by the enzyme invertase.
  2. Conversion into ethanol and CO2.Glucose and fructose are then converted into ethanol and CO2 through a series of biochemical reactions. This process is calledglycolysis and occurs in the cytoplasm of yeast cells. Glycolysis produces pyruvic acid, which is then converted to ethanol and CO2 by other specific enzymes.

The speed of fermentation of a dough depends on a few factors, for example:

  • Quantity and quality of yeast.With a suitable amount of yeast (2-4%) you will get optimal vital activity and fermentation will be fast. Be careful not to overdo it, however: if the yeast exceeds 6% of the amount of flour, it will have an opposite effect.
  • Recipe.The higher the hydration rate of the dough, the greater the fermentation activity of the yeasts.
  • Method of preparation.Doughs prepared by the indirectmethod (biga or poolish) ferment faster than those prepared by the directmethod.
  • Environmental conditions.The higher the temperature and humidity the faster the yeasts ferment. But be careful, the temperature should not exceed 38°C: above 40°C theSaccharomyces begin to activate and, upon reaching 50°C, they stop their metabolism completely.

With regard to yeast products, the CO2 produced duringalcoholic fermentation is particularly important because it is responsible for the rising of the dough. Carbon dioxide is released as gas inside the dough, creating bubbles that make it softer and lighter. This is why bread, pizza and other baked goods have a honeycombed structure and a soft texture.


There are some interesting, but most of all useful trivia and tricks to use while fermenting your doughs.

  • The multiplication of yeast cells is more active if their initial amount is small. Some laboratory tests have revealed that if the flour in the dough contains 0.5 percent yeast, the increase in cell mass will be as much as 88 percent, while with 2 percent the growth is reduced to as low as 29 percent.
  • The cell multiplication of yeast is stimulated by the presence of some important substances that are necessary for their metabolism: vitamins and mineral salts are found naturally in stone-ground flours, while in very refined flours they are found in low proportions, consequently it may be necessary to add them to promote the multiplication of yeast and its subsequentfermentation.
  • The optimum temperature for yeast multiplication is 25-30°C, while their maximum fermentation activity is reached at 35°C.
  • The required humidity for yeast is about 80%. A home system to achieve the required humidity level is to create a leavening cell in the oven (at minimum) by placing a bowl of lukewarm water in the bottom or by covering the bread with clingfilm, placed in the oven at minimum) so that it generates the humidity itself by leavening.

Thefermentation is one of the oldest and most fascinating culinary techniques in the history of cooking, capable of still surprising us with its ability to transform simple ingredients into foods rich in flavor, nutrition and health benefits. But it doesn't end there! This is only a part of this vast world, we invite you to continue the discovery of this fascinating world in the second part where we will delve into techniques, recipes and secrets to successfully experiment with this age-old practice in your own kitchen.

Blog edited by Enrico Gumirato pastry chef and trainer.

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