The leavening is a fundamental biological process in the preparation of many foods — bread, pizza, cakes and other baked goods — that transforms a dense, compact dough into a soft, fluffy final product with a pleasant taste. The magic of leavening lies in the activity of microorganisms, mainly yeasts, that act on the ingredients of the dough, producing the gases that increase its volume.
But leavening… what is it?
Leavening begins when yeast, a single-celled fungus, is added to the dough. The most commonly used yeasts are Saccharomyces cerevisiae, for baked goods, and Saccharomyces pastorianus, for the production of beer and wine. These microorganisms feed on the sugars in the flour, turning them into ethyl alcohol and carbon dioxide through a process known as alcoholic fermentation. It is the carbon dioxide produced that makes the dough swell, creating the characteristic air bubbles that make bread and other leavened products soft and light.
There are 3 types of leavening:
- Physical leavening. Physical leavening is a process that does not involve chemical reactions or the activity of microorganisms such as yeasts, but relies on introducing air, or steam, into a dough. A classic example of physical leavening occurs when egg whites are whisked to stiff peaks: whisking the egg white incorporates many tiny air bubbles which, once in the oven, expand with the heat, making the final product soft and light. This type of leavening is typical of certain cakes made with whisked egg whites, where there is no need to add yeast because the volume and softness are guaranteed by the air trapped during whisking.
- Chemical leavening. Chemical leavening is a process that makes doughs and mixtures swell and rise without the use of microorganisms such as yeasts. This type of leavening occurs thanks to the chemical reaction between two substances: an acid and a base. When these two substances meet, in the presence of moisture (such as the water in the dough), they react and produce carbon dioxide (CO2), which forms tiny bubbles inside the dough that make it swell and become softer and lighter. The chemical leavening is widely used in the making of desserts such as cakes and muffins, thanks to its ability to act quickly and require no waiting time for rising.
- Biological leavening. Biological leavening is a natural process that makes doughs swell and rise, such as those for bread or pizza. This happens thanks to the action of living microorganisms, mainly yeasts and lactic acid bacteria, which feed on the sugars in the dough. As they eat these sugars, they produce carbon dioxide (CO2) and ethyl alcohol through a process called alcoholic fermentation. The carbon dioxide that forms creates bubbles inside the dough, making it swell and become softer and lighter. The biological leavening not only helps give volume and softness to baked goods, but also helps improve their flavour and digestibility
Natural or biological leavening?
Between the terms biological leavening and natural leavening there is a bit of confusion; they are often taken to be the same process, but they are not the same thing.
- The biological leavening is a natural process that occurs through the activity of microorganisms such as yeasts and lactic acid bacteria, which convert the sugars in the dough into carbon dioxide and ethyl alcohol via alcoholic fermentation.
- The natural leavening refers to the use of sourdough starter or mother dough: a mixture of water and flour left to ferment naturally. This type of yeast is not made up solely of Saccharomyces cerevisiae (baker's yeast), but includes a variety of species of Saccharomyces, Candida and various lactic acid bacteria such as Leuconostoc, Lactobacillus and Weissella. These microorganisms work together to ferment doughs, and the result is a baked product with a richer, more complex flavour and texture, as well as better shelf life.
While biological leavening describes the general process involving living microorganisms, natural leavening focuses more specifically on the use of a sourdough starter that contains a variety of microorganisms and helps create a distinctive flavour and texture in the final product.
5 things to watch for good leavening
Various factors can affect how effective leavening is, including:
- Temperature. The optimal temperature for leavening is around 25°C to 30°C. Temperatures that are too low slow the process down, while those that are too high can kill the yeast.
- Type of yeast. There are various types of yeast, including fresh, dry and instant yeast, each with its own characteristics and activation times.
- Amount of yeast. The amount of yeast used affects the leavening time; more yeast can speed the process up, while less yeast takes longer.
- Humidity. A humid environment favours leavening: if your surroundings are very dry, we recommend placing a small bowl of water in the oven during baking to keep a good level of moisture.
- Additional ingredients. Ingredients such as sugar can encourage leavening, while salt can slow it down: this is why it is important not to mix yeast and salt directly.
The leavening is a complex process that determines whether a cake or a loaf of bread turns out well, but it is also a culinary adventure that everyone should try at least once in their life! Yes, there are several factors to consider, but don't let it intimidate you!
Whether you are a beginner or an experienced cook, remember: every great journey begins with a single small step. Make this moment your own, switch on the oven and get ready to amaze yourself and your friends with your soft, light baked goods. The art of leavening is waiting for you — are you ready to take up the challenge?
