Pizza Dough Fermentation Explained: Understanding the Science Behind It

Understanding the science of fermentation is key to mastering pizza dough, transforming it from a simple mixture of flour, water and yeast into a complex, flavorful foundation for your pizza. In this article, we will learn why long fermentation is crucial for pizza dough, exploring how it enhances flavor and texture while covering all the processes the dough undergoes during fermentation

Pizza Dough Fermentation: Introduction

Before we begin, it is important to note that the processes and scientific principles behind dough fermentation are vast and complex. They involve a range of disciplines such as biology, chemistry, and biochemistry, and encompass numerous reactions among the various components involved in the fermentation process.

Consequently, it is not possible to fully summarize everything in a single article. However, I have made an effort to ensure that this article is both informative and accessible to readers without a scientific background.

Please note that throughout this article, unless otherwise specified, the term “fermentation” refers to the entire process that the dough undergoes, from the end of kneading to baking. Additionally, all the information presented in this article is applicable to any type of dough leavened with yeast (including sourdough).

What Is ‘Fermentation’?

Before we proceed, it is important to have a clear understanding of the term ‘fermentation’. The process we refer to as ‘fermentation’ involves two main factors/processes:

• The rising of the dough
• The maturation of the dough (also known as “ripening”)

These two processes occur simultaneously and continuously from the end of kneading until the baking stage.

Let’s begin by clarifying the terminology for these two terms:

• Rising: This refers to the physical expansion of the dough, which is the result of yeast activity and the accumulation of gases (CO2).
• Maturation: This refers to various chemical and biochemical processes that take place in the dough during fermentation. These include enzyme activity in the dough, as well as the activity of yeast and bacteria.

Dough Rising (Increase in Volume)

Those responsible for the “rising of the dough,” which refers to the physical increase in volume of the dough, are exclusively the yeast (or in the case of sourdough, yeast and lactic acid bacteria – more on these later).

Yeast is a living, single-celled organism, and despite being seemingly the simplest form of life, its activity in the dough is complex and significant.

How does yeast make the dough rise in volume? In short:

1. Most of the flour (about 70%) is composed of starch (a complex carbohydrate).
2. Enzymes naturally present in the flour break down the starch (and other complex sugars found in the dough) into simple sugars (specifically glucose and fructose).
3. The yeast consumes these sugars and produces carbon dioxide (CO2) and alcohol (ethanol). The carbon dioxide becomes “trapped” in the gluten network (more precisely, in the tiny air pockets created during kneading), causing the dough to pyisically rise and increase in volume.

To conclude: Complex carbohydrates (starch and other complex sugars) → Simple sugars → Yeast consumes these sugars → Production of carbon dioxide → Dough increases in volume

In general, the more yeast we use in the dough, the greater the amount of CO2 produced in the dough will be, and the faster it will physically rise and increase in volume.

Dough Maturation

The maturation of dough refers to the additional chemical and biochemical processes that occur during fermentation, in addition to the physical rising caused by the yeast and the production of gas (CO2). These processes include:

• Enzymes breaking down proteins in the flour into amino acids, which are the building blocks of proteins. These amino acids directly and indirectly affect the flavor of the dough and the browning during baking through the Maillard reaction.
• Starch being broken down into simple sugars, which serves as food for the yeast.
• The “softening” of the dough by breaking down the gluten bonds (the gluten-forming proteins).
• An increase in acidity (lowering of the pH) in the dough.
• Production of acids, organic compounds, and aromatic compounds that influence the flavor of the dough.
• The activity of lactic acid bacteria, whose by-products impact the flavor of the dough.

The level of dough maturation has an effect on both the behavior and texture of the dough, due to the break down of gluten, as well as on flavor, due to the by-products produced during the fermentation process.

Unlike the rising process (which can be “manipulated” by using more yeast in the dough), the maturation process of the dough primarily depends on time. While higher temperatures can accelerate the activity of enzymes and other organisms in the dough, there is no effective way to speed up the maturation process to align it with the physical rising process other than allowing it to ferment for an extended period of time. This is one of the main reasons we do long fermentations – to achieve a dough that has properly risen AND matured.

Gas Production vs Gas Retention

It is important to distinguish between the production of gases (CO2) by the yeast and the ability of the dough to retain these gases.

As mentioned earlier, gas production depends solely on the activity of the yeast, while the ability to retain gases in the dough relies on the characteristics of the dough, specifically the state of the gluten. For example, a dough that is more elastic and resistant will have a higher capacity to retain gas, whereas a weaker, overly extensible dough will have a lower ability to do so.

Our ultimate goal is to achieve a balance between gas production and gas retention. This will result in a structure that is sufficiently strong to effectively trap the gas (“air bubbles”) inside, while still being able to expand and increase in volume during baking.

If the dough is too elastic without enough extensibility and stretch, it will not expand adequately during baking (due to the gluten’s resistance to stretching). On the other hand, if the dough is too extensible without the necessary elasticity and strength, it will be unable to retain the gases formed during fermentation.

The Fermentation and Maturation Processes in Pizza Dough

Now that we have a general understanding of what fermentation is, let’s explore the specific processes that the dough undergoes during fermentation. We will focus on two key aspects:

1. The yeast’s activity during fermentation, including the role of the enzymes in the flour that provide the yeast with food.
2. The maturation processes of the dough, particularly the breakdown of proteins (gluten) and the formation of organic acids.

Yeast Activity During Fermentation

Aerobic and Anaerobic Activity of Yeast

The activity of yeast in the dough can be divided into two ‘stages’:

1. Aerobic fermentation (in the presence of oxygen)
2. Anaerobic fermentation (when there is no oxygen present in the dough)

Aerobic fermentation primarily occurs during the initial stage of fermentation when the yeast “multiplies” by dividing and germinating. During this stage, the yeast utilizes glucose and oxygen to generate energy and reproduce.

The by-products of aerobic fermentation are carbon dioxide (CO2) and water. No alcohol or ethanol is formed at this stage.

Anaerobic fermentation, also known as “alcoholic fermentation”, takes place when there is no oxygen in the dough. The yeast then exclusively consumes glucose to produce energy.

The by-products of anaerobic fermentation are CO2 and alcohol (ethanol). This is the stage we commonly refer to as “dough fermentation”.

During anaerobic fermentation, the yeast may still multiply, although studies are divided on whether they actually multiply in the dough during this phase. Some studies show an increase of up to 90% in yeast cells after a few hours, while others find no difference in yeast cell count even after 8 hours. Did I already mention yeast is a simple yet complex organism?

In terms of “timeline”, the two phases can be divided as follows:

1. During kneading, oxygen becomes trapped inside the dough, allowing the yeast (or bacteria in the case of sourdough) to carry out aerobic fermentation. This process also causes the dough to oxidize. Oxygen is quickly consumed by the yeast, so this stage lasts for a very short period, typically no longer than an hour after kneading.
2. Once the oxygen supply in the dough is depleted, the yeast switches to anaerobic/alcoholic fermentation.

The ideal temperature range for the anaerobic phase is between 20-27°C / 68-80°F, with the optimal temperature being 26°C / 79°F. This is one of the reasons why we aim for a final dough temperature of 23-27°C / 75-80°F.

Breakdown of Starch in the Dough into Simple Sugars Used as Food by the Yeast

Yeast, like any other living organism, requires food to survive and function. This ‘food’ primarily consists of simple sugars, particularly glucose. During fermentation, yeast consumes the glucose present in the dough (we will explore how it is produced shortly), and produces the by-products we refer to as ‘fermentation’: carbon dioxide, alcohol, and organic acids.

..But how exactly does this process occur?

Flour naturally contains enzymes whose ‘purpose’ is to break down the starch in the flour into simple sugars (glucose units) that the yeast can consume. The two enzymes responsible for breaking down the starch in the dough and providing food for the yeast are alpha-amylase and beta-amylase.

The diagram below illustrates the process of breaking down the starch in the dough by the amylase enzymes into simple sugars:

1. Starch is composed of a long chain of glucose molecules, which serve as the primary source of energy for our bodies (and most living organisms), just like yeast. Glucose is one of several monosaccharides that can be absorbed directly by our intestines without needing any further breakdown. Yeast can only consume individual glucose molecules.
2. The enzyme alpha-amylase can break down the long glucose chain (starch) at any point.
3. The enzyme beta-amylase can only break down the two end molecules in the chain (two molecules from the right/left side), resulting in the production of maltose (two glucose molecules).
4. The enzyme maltase breaks down maltose into two individual glucose molecules, which the yeast can then consume to produce energy (with the byproducts of this process being CO2 and ethanol).
5. Other polysaccharides (complex sugars) also undergo a similar breakdown process, facilitated by other enzymes. For example, sucrose (table sugar) is broken down by the enzyme invertase.

To generate energy, yeast consumes monosaccharides, mainly glucose and fructose, but it can also consume maltose (a disaccharide) by breaking it down with its own maltase enzymes. Starch, which is made up of a long chain of glucose molecules, needs to be broken down into individual glucose molecules for the yeast to use as an energy source.

This is where the alpha-amylase enzyme comes in – it breaks down the long starch chains into shorter ones at any point along the chain.

The activity of the alpha-amylase enzyme is crucial to the fermentation process because it provides more areas for the beta-amylase enzyme to act on. Beta-amylase can only break down the ends of the chain. With more areas of action, the starch is broken down into maltose more quickly, resulting in many smaller chains that beta-amylase can act on, rather than one long chain that can only be broken down at the ends.

For fermentation and maturation to occur, yeast needs a supply of glucose, fructose and/or maltose as its food source. Any remaining glucose/fructose molecules in the dough act as residual sugar and contribute to browning during baking.

The main catalyst for breaking down the starch in the dough into sugars is the alpha-amylase enzyme. Therefore, when we refer to enzymatic activity in flour, we are specifically talking about the activity of the alpha-amylase enzyme. The higher the presence of alpha-amylase enzyme in the flour, the more starch will be broken down, providing more food for the yeast and affecting the speed of fermentation (more food available means faster fermentation).

In this context, it is important to note that the alpha-amylase enzyme has a higher affinity for and acts more rapidly on damaged starch (which, as the name implies, has been ‘damaged’ during the milling process) rather than intact starch. Consequently, the majority of starch breakdown in the dough occurs due to alpha-amylase activity on damaged starch.

Standard flour usually contains 5-8% damaged starch, which is the maximum “threshold” for starch conversion into sugars within the dough.

The Maturation Process in Pizza Dough

Breakdown of Proteins (Gluten) in the Dough

The breakdown of proteins (gluten) in the dough is crucial for both the texture and rheological properties of the dough (how it feels and behaves – soft, resistant, stretchy, etc.), as well as for impacting the flavor of the final product. Protease enzymes are primarily responsible for breaking down the proteins in the dough, along with acids (to a lesser extent).

Protease enzymes, also known as proteolytic enzymes or “proteases”, naturally occur in flour and are also produced by yeast and bacteria during fermentation. They are active from the moment the dough is mixed until baking, and play a central and essential role in the fermentation process. They break down and weaken the gluten structure by breaking down the gluten-forming proteins, into:

• Amino acids (the building blocks of proteins)
• Peptides and polypeptides (chains of amino acids of different lengths)

The process of breaking down the proteins in the dough is called proteolysis. It softens the dough by weakening the gluten structure and makes it easier to work with. This also affects the dough’s elasticity and extensibility properties, as well as the final texture of the pizza crust (soft, chewy, leathery etc.).

In addition to breaking down the gluten structure and softening the dough, the breakdown of proteins into amino acids significantly affects the flavor; This is because it “produces” amino acids and peptides as a result of the gluten breakdown:

1. Amino acids are essential for the Maillard reaction (browning) during baking, which gives the pizza crust deep and complex flavors.
2. Amino acids interact with other components in the dough, primarily alcohol and organic acids, through a chemical reaction. This interaction leads to the formation of flavor and aroma compounds that directly impact the dough’s flavor and aroma.

In simpler terms, the flavor potential of the dough increases as more proteins are broken down into amino acids. Unfortunately, this natural process cannot be artificially sped up and requires time.

It is important to note that the activity of protease enzymes in the dough is desirable up to a certain point. If the protease enzymes work for too long, they will excessively break down the gluten in the dough, resulting in a weak gluten structure, excessive extensibility, a liquid consistency, and easy tearing – essentially, an over-fermented dough.

In terms of maturation, a “ripe” dough is one in which the proteins (gluten) have been sufficiently broken down. This allows for achieving a dough that is easy to shape and stretch before baking. The ideal dough has a balance between extensibility and elasticity, meaning it stretches easily without tearing, yet remains strong enough and has sufficient elasticity.

It is important to note that the type of flour used also affects the degree of gluten breakdown required by the proteolytic enzymes and acids. A dough made from flour with a higher protein (gluten) content will require longer protease activity compared to dough made from lower protein flour. You can find more information about this topic in the following article: The Ultimate Guide to Pizza Flour – How to Choose the Ideal Flour for Pizza.

There are dough conditioners/reducers available that “mimic” the action of protease enzymes in the dough. These additives essentially ‘artificially’ soften the dough and shorten its maturation time. Examples of such dough conditioners include L-cysteine and glutathione (‘dead yeast’). However, these dough conditioners only help in softening the dough, and they generally do not impact flavor (they break/weaken the gluten bonds but do not break down proteins into amino acids).

Acids, Acidity and Lactic Acid Bacteria

During fermentation, several organic acids are formed in the dough, including lactic, acetic, succinic, fumaric, pyruvic, propanoic, butyric, valeric, and caprylic acids.

In the context of fermentation, the two acids of particular interest to us are lactic acid and acetic acid. These acids are primarily produced by lactic acid bacteria (LAB), and to a lesser extent by yeast.

Lactic and acetic acids play a significant role in determining the flavor of a long-fermented dough:

• Directly: Lactic acid contributes a mild, yogurt-like flavor to the dough, while acetic acid adds a sharp, vinegar- or lemon-like flavor.
• Indirectly: Chemical reactions between these acids and other components in the dough, especially alcohol, lead to the formation of aromatic compounds.

Aside from flavor, the presence of these acids in the dough also lowers the pH (increases acidity) and influences other aspects of the dough’s maturation process:

• Texture: Acidity strengthens the gluten bonds, affecting the dough’s texture and handling properties.
• Effect on other processes in the dough: Acidity affects enzymatic activity in the dough, including the activity of yeast, LAB, and protease enzymes. All of these prefer a more acidic environment, which leads to an increase in their activity as the dough becomes more acidic.

When discussing lactic acid bacteria (LAB), we are referring to a group of bacteria that produce lactic (and other) acids, rather than a single strain of bacteria. Within this group, there are various strains of bacteria with different properties and effects on the dough. This is the primary reason why different sourdough starters behave differently – their composition, or the ‘microflora’ (the population of microorganisms), varies from one sourdough starter to another.

In dough made with baker’s yeast, the activity of LAB is significantly lower compared to the activity of the yeast cells. For every single LAB bacterium, there are between 10,000-100,000 yeast cells. Therefore, time is a crucial factor for LAB to produce lactic and acetic acids in sufficient quantity to affect the flavor of the dough.

Unlike baker’s yeast, which scientists have been able to isolate and “engineer” to achieve optimal leavening and fermentation of dough, LAB have not been as cooperative. As a result, the only way to obtain the products of their activity in the dough is to allow them sufficient time to work, or in other words – to perform a long fermentation (or use sourdough).

Due to their low presence in dough made with baker’s yeast, LAB require time to achieve their desired effects. Therefore, it is crucial to allow the dough to ferment for an extended period (while adjusting the amount of yeast based on the fermentation duration and temperature, which can be done using PizzaBlab’s pizza dough calculator).

This is also why preferments are allowed to undergo a prolonged maturation process with minimal yeast usage. The combination of these two factors provides an optimal environment for LAB to thrive and maximize their by-products.

From a technical standpoint, in order to achieve sufficient activity of LAB, it is necessary to let the dough ferment for at least 6-8 hours at room temperature or 48 hours in the fridge.

LAB can be classified into two ‘subcategories’:

• Homofermentative LAB – lactic acid bacteria that primarily produce lactic acid (“Homo” means “same”).
• Heterofermentative LAB – lactic acid bacteria that produce a combination of lactic acid, acetic acid, and carbon dioxide. Typically, lactic acid is the predominant product, with acetic acid and carbon dioxide produced in smaller quantities (“Hetero” means “diverse”).

The main difference between the two groups is their temperature preference:

• Homofermentative bacteria prefer relatively high temperatures (between 20-40°C/68-105°F, with the ideal temperature being around 30°C/86°F) and a more liquid environment (higher dough hydration).
• Heterofermentative bacteria prefer relatively low temperatures (below 20°C/68°F), and a drier environment (lower dough hydration).

In other words: fermentation at lower temperatures will prioritize the activity of heterofermentative LAB (which results in the production of more acetic acid), while fermentation at higher temperatures will prioritize the activity of homofermentative LAB (which results in the production of more lactic acid).

The type of acid produced has a direct and indirect effect on the flavor and texture of the dough. A future article will be published, providing a detailed explanation of how the various acids produced during fermentation impact the dough.

Acidity and Its Impact on Gluten

Beyond its effect on flavor, acidity in the dough also serves another equally important purpose: strengthening the gluten.

The exact mechanism by which acidity strengthens the gluten is beyond the scope of this article as it is too complex. In short, increasing acidity (up to a certain point) causes the bonds between the gluten-forming proteins to tighten, resulting in a stronger and more elastic gluten structure. This is why preferments enhance dough strength, and why dough made with sourdough always feels stronger and more elastic.

However, acidity in this context can be a double-edged sword. Excessive acidity, such as in over-fermented dough, can actually damage the gluten structure. This occurs indirectly by accelerating the activity of protease enzymes that break down gluten (which are more active in a more acidic environment), and directly by breaking down and weakening the bonds between the gluten-forming proteins.

Why is Long Fermentation Necessary in Pizza Dough?

The main reason for conducting a long fermentation is to enhance flavor. The main outcome (and purpose) of dough that has undergone an extended period of fermentation is the creation of distinct aromas and flavors, which can only be achieved through a prolonged fermentation process (or by using a preferment). The deep and complex flavors that develop in dough that has undergone extended fermentation, cannot be replicated using any other method.

And what about the “healthiness” or “better digestibility” of long-fermented dough? A detailed article on this topic will be published in the future (spoiler alert: this is nothing more than a myth).

What is the Ideal Fermentation Time for Pizza Dough?

There is truly no “right” answer to this question. In terms of flavor development, the “standard” fermentation durations for cold fermentation are 24-72 hours, with 24 hours being the “minimum”. For room temperature fermentation, it ranges between 6-24 hours. A detailed article about cold fermentation and room temperature fermentation will be published in the future.

Obviously, more fermentation time results in more flavor. However, it’s crucial to understand that the dough cannot be fermented indefinitely. The byproducts of fermentation, particularly the activity of protease enzymes, will eventually break down the gluten in the dough too much, resulting in an over-fermented dough.

The amount of fermentation time the dough can handle largely depends on the flour used (all other things being equal). For more information on this topic, refer to the following article: The Ultimate Guide to Pizza Flour: Characteristics, Differences, and Choosing the Ideal Flour.

It is important to note that when it comes to flavor in the dough (whether it was made with sourdough or baker’s yeast), “more flavor” does not always mean “better” (if you have ever had food with too much seasoning, you know what I mean).

Flavor is subjective, and what one person enjoys may not taste good to another. A dough fermented for 48, 72, or 100 hours may not necessarily have a “better” flavor compared to a dough fermented for a shorter time (however, it may be more prone to mishaps/errors along the way).

The key point is that there are multiple ways to make pizza, and there isn’t just one correct method (although there are more convenient and easier approaches that yield consistent and predictable results).

If you don’t notice a difference between a dough fermented for 3 hours at room temperature and one fermented for 72 hours in the fridge, that’s perfectly fine (in fact, it means making pizza whenever you want will be much easier for you).

I recommend experimenting with different fermentation times, particularly longer room temperature fermentations, and see what works and tastes best for you. You might be pleasantly surprised by the results.

Now that you have a clear understanding of how fermentation works, you can proceed to the next article, which focuses on effectively controlling the rate of fermentation: How Much Yeast to Use in Pizza Dough: Factors Affecting Fermentation Rate.