What Does Yeast Do To Bread? Bread Fermentation Process

The dough fermentation process is the science behind how flour, water, salt and yeast come together and transform into bread. This article reveals how important dough fermentation is and deep dives into what yeast does to bread and the overall science of bread making. The majority of bakers won’t know this information. And, neither did I. But after taking some time out to understand what was really going on – the quality of my bread skyrocketed!

Knowing the science behind baking bread allows you to cut through the bad advice found online and make better choices. After reading this detailed guide you’ll know how bread fermentation works and understand its importance in making consistent quality bread. We’ll also touch on how flour breaks down during the dough production process to develop the gluten structure and provide food for the yeast.

Hey there! Some links on this page are affiliate links which means that, if you choose to make a purchase, I may earn a small commission at no extra cost to you. I greatly appreciate your support and I hope you enjoy the article!

What is fermentation?

Fermentation comes from the Latin word “Fermentare”, meaning “to leaven.” It is an important stage in many popular food products such as cheese, yoghurt, alcohol, pickled foods and bread. For fermentation to occur, a base and a strain are required. A base will be a form of carbohydrate, and the strain is a type of bacteria or fungus.

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In bread fermentation, the base is the carbohydrates in the flour, and the strain is yeast.

Bread fermentation simplified

As soon as yeast comes into contact with flour and water, the yeast fermentation process begins.

The hydrated carbohydrates break down into simple sugars. These sugars will supply the yeast with food for it to aerobically and anaerobically respires. Carbon dioxide is the product most associated with yeast respiration as it expands the pockets of gluten (alveoli) to make the bread rise.

We can make changes in how we handle the dough and the fermentation process to create open, irregular, or close-knit crumb types. Larger air pockets make an open crumb bread with a lighter texture.

However, it’s not this simple. Alcoholic fermentation, instigated by the yeast generates other components including ethanol, lactic acid, acetic acid and various organic acids. How this happens and how to control levels of alcoholic fermentation vs simply carbon dioxide production takes a bit of effort to understand. But not to worry, you’re in the right place!

What is yeast?

Yeast is a single cell organism of the fungus species. Although modern yeast production has been around since the early 1800s, the use of wild yeasts has been around for tens of thousands of years. Sourdough, the original levain used to ferment bread has been traced back to ancient Egyptians and beyond.

There are 1,500 types of yeast, and many strains of each version. The one used in all types of bread yeast is Saccharomyces Cerevisiae. This yeast is also often found in sourdough starters and strains of Saccharomyces Cerevisiae are used to ferment beer.

Yeast is dormant in the case of active dry and instant yeasts until it is hydrated in water. Fresh yeast contains a much higher ratio of water is more active. It is kept “alive” by storing it in the fridge. At cool temperatures, there is very little yeast activity, more on this later!

To find out how sourdough works, check out the sourdough fermentation process article.

How sugars are supplied to the yeast

Carbohydrates make up around 60-70% of bread flour. If you’re not aware of how carbs work or don’t recall biology from school, here’s a short overview:

There are three forms of carbohydrates; simple sugars, starch and dietary fibres. They are composed of the same sugar elements but take on different forms through the combinations of molecules and the size of the chains.

Simple sugars

Simple sugars are the simplest form of carbohydrate. They consist of single cell, monosaccharides (also known as hexose sugars), and double cell, disaccharides. These sugars need little breaking down to be absorbed through cell walls.

As they are quickly absorbed into our bodies bloodstream they provide a quick burst of energy. This makes them not great for our bodies if consumed in high doses, but ideal for a simple organism like yeast.

Glucose, fructose and galactose are monosaccharides. Maltose, sucrose (table sugar) are disaccharides, formed by bonding monosaccharides.

Awkwardly, not all of these sugars taste sweet. In naturally occurring ingredients such as honey or jam, it is common to find a combination of monosaccharides and disaccharides. The main sugars in flour are glucose, fructose, sucrose and maltose.


These more complex carbohydrates are formed by strings of monosaccharides and disaccharides connected by glycosidic bonds. Starches or polysaccharides are broken down by enzymes found in bread dough to become simple sugars. The main enzymes used in breadmaking are amylase and invertase. Without breaking down,  a starch’s complex make-up means it doesn’t have a sweet flavour.

Starch is produced by vegetables to store energy. Many other uses of starch are explained in this video:

Dietary Fibres

Dietary fibres are the most complex strings of sugars. They are too complex to break down and digest easily. It takes a lot of time and energy to unlink these chains of sugars for digestion. Eating high fibre food is recommended by experts to aid our digestion systems. It acts as a carrier to remove waste from our bodies.

The bran is the largest source of dietary fibre in bread. This makes white flour, which has a majority of the bran removed less good for you and one of the reasons why whole wheat bread is best.

The enzymatic action of yeast

There are few simple sugars available in flour so the starch and fibre chains must be broken down into disaccharides. Next, the disaccharides are broken into monosaccharides which supply the yeast.

To break down the starch, yeast naturally produces enzymes – This is where things start to sound a little confusing!

  • Amylase breaks down starch into the disaccharide Maltose which consists of two bonded glucose sugars.
  • Maltose is broken down by the Maltase enzyme and we are left with glucose.
  • Also, the enzyme, Invertase breaks down a disaccharide called Sucrose (table sugar) into two monosaccharides, glucose and fructose.
How starch is broken down in bread dough

The glycolysis process

Even monosaccharides are still too large to penetrate the yeast cell walls for respiration (yeast respiration comes before fermentation). The glucose cells undergo a process called glycolysis. Here the glucose cells are broken down into two Pyruvates and release energy in the form of ATP (Adenosine Triphosphate). The Nicotinamide Adenine Dinucleotide molecules that are produced during glycolysis will be used in both lactic acid and alcoholic fermentation. From here there are a few possible outputs.

Aerobic respiration vs Anaerobic respiration

As the simple sugars undergo glycolysis. The pyruvates produced are supplied to the yeast with the presence of oxygen or without.

Aerobic respiration

With oxygen in the process, after glycolysis, the second step of aerobic respiration follows the Krebs cycle. Here, the oxidised pyruvates enter a cyclic process that follows a chain of reactions. The result is carbon dioxide, water and lots of energy through ATP are produced.

Anaerobic respiration

The output of anaerobic respiration leads to the sugars being fermented through alcohol fermentation or lactic acid fermentation. Yet, at this point, there is no fermentation occurring. The yeast is simply consuming the pyruvates with or without oxygen, but it’s about to begin!

As you can see in the diagram below, aerobic respiration produces much more energy than respiration that occurs without oxygen.

Aerobic respiration vs fermentation

The 3 ways yeast can ferment

There are 3 options for the yeast after anaerobic respiration. They do are have some properties in common:

  • They all produce heat
  • They release energy but not nearly as much as aerobic respiration
  • They all occur in the cytosol.

1- Alcoholic fermentation

Alcoholic fermentation is a metabolic reaction that uses the pyruvates produced from glycolysis to make ethyl alcohol and carbon dioxide.

Initially, the pyruvate is catalyzed by the enzyme Pyruvate Decarboxylase and then by Alcohol Dehydrogenase. The result is ethanol and carbon dioxide.

Contervously, carbon dioxide doesn’t appear as a gas at first. It begins as a liquid that travels through the gluten structure to a point of weakness to take on a gas form.

2- Fermentation to produce lactic acids

Aside from yeast respiration, the enzymes in the dough also break down carbohydrates to produce Lactic Acid Bacteria (LAB). The bacteria utilise the available sugars to undergo homofermentative or homolactic fermentation.

When combined with sugar in a homofermentative reaction, LAB produces lactic acids.

In homolactic fermentation, two lactic acid molecules are generated by the action of the enzyme Lactate Dehydrogenase. Again, like yeast, there are many types of lactic acids that can be produced, Lactobacillus Casei is a common one found in breadmaking.

3- Fermentation to produce acidic and lactic acids

10% of LAB undergoes a different process called a heterofermentative reaction. This follows a process called the Phosphoketolase pathway. This is where oxygen is used in the process to produce acetic acid as well as lactic acid, ethanol and CO2.

The outputs are produced with the aid of both Lactate Dehydrogenase and Pyruvate Decarboxylase enzymes. A popular acetic acid that you might have heard of is Lactobacillus Sanfranciscensis. This is a core feature of unique sourdough bread made in San Franciso. Acetic acid is the key component of vinegar.

Other acids are also produced and categorised as “various organic acids”.

The benefits of organic acids produced in bread

The effect that lactic acid has on the dough as it ferments
How organic acids improve the dough during fermentation

Besides the production of CO2, organic acids change the physical properties of the dough in many ways. Organic acids are essential to making bread, without them bread wouldn’t be nice to eat. They improve the dough’s ability to:

  • Hold shape
  • Stretch (extensibility)
  • Retain gas
  • Produce gas
  • Stay fresh for long after baking
  • Produce deeper flavours and aromas
  • Lowers Ph value

As yeast respiration and fermentation continues, carbon dioxide, ethanol and organic acids multiply. They work in harmony with each other taking and breaking down the sugars each requires.

Is ethanol needed in bread dough?

Ethanol produced during fermentation is not a by-product of the process. It is absolutely necessary to mature the dough. In bread, ethanol improves odour, flavour and keeping quality. During baking, much of the ethanol evaporates, but traces can remain. If your bread smells too much like alcohol, it’s probably over-proofed.

Is oxygen good for bread?

Before we understand how to control bread fermentation, it’s important to consider the pros and cons of aerobic and anaerobic respiration.

Oxygen is incorporated during kneading. If a faster, more aggressive kneading technique or speed is used, the dough incorporates more oxygen. If the dough is gently mixed, less oxygen is incorporated. Once oxygen supplies expire, the yeast switches to anaerobic respiration and the dough ferments.

It is also a sensible point to highlight how low simple sugar content can also cause aerobic respiration to end and anaerobic to take over. This often happens in whole wheat doughs as the flour needs more time to soak and break down into simpler sugars. It can be counteracted by adding table sugar or soaking some (or all) of the flour in the form of an autolyse, soaker or preferment.

As more energy is produced during aerobic fermentation gas is produced at a faster rate. This means that for quick-breads, introducing oxygen to the dough is vital.

TypeSuitable forProsCons
AerobicQuick bread and rolls Bread rises faster and improved oven spring.

Bread has a lighter flavour and a soft texture.
Heavily oxidated dough will weaken and collapse if proofed for too long.

Less aromatic and short shelf life.
AnaerobicArtisan breadHigher organic acid content so more flavour, better shelf-life, improved crumb structure.Flavour can be overpowering.

Production time is increased.

Where does fermentation occur in bread making?

StageProcessEnds when
PrefermentThe optional step of preparing a preferment starts the fermentation.

Here a portion of the flour is matured with water and a small amount of yeast. 

Yeast fermentation matures the flour to produce a prefermented dough. 
After 12-18 hours (typically) it is added to the main dough.

When the preferment is ready to use it will have bubbles throughout, and on the surface.

Expect a preferment to at least double in size in most cases.
First riseThe dough matures through yeast fermentation to produce organic acids.

Organic acids improve the gluten structure as does awarding the gluten time to naturally develop.
Depending on the bread made, the first rise can be short, or zero if the baker wishes to benefit from aerobic fermentation.

For more maturation, a longer period of bulk fermentation can take place.

The length of bulk fermentation is measured by the height of the rise. This varies between bakers and recipes from 20% to 100% of the doughs original size.
ProofingAfter shaping, the dough is proofed for the final time. As time goes on, the process of enzymatic and fermentation activity continues and until the bread is deemed ready to bake.The dough rises until the simple sugars are exhausted. At this point, the dough is proofed and ready for the oven.

The dough can over proof if the gluten structure becomes so filled with gas it becomes too heavy to support itself, or lactic acid begins to consume the gluten and the structure breaks down.  
Oven springYeast activity continues in the oven as it consumes the remaining sugars rapidly in the warmth of the oven.

The oven spring lasts for around 10-15 minutes and is vital for light crumbed bread with a crunchy crust.

For crusty bread, water is added to the oven to produce steam.  
As the bread bakes, the temperature gets too high for maltase to break down enough monosaccharides for the yeast to feed on which slows the oven spring.

The oven spring ends when the core of the bread gets too hot for the yeast (yeast kill point) and/or the crust sets (crust set point).

How to end yeast fermentation?

Yeast is a fungus, a tiny living organism. All it wants to do is have a good feast and multiply. Like other fungi and bacteria, once they get too hot they become permanently inactive. When the oven temperature reaches 68C (155F) the yeast cells die, bringing yeast fermentation to an end. This is the Yeast Kill Point.

How to change the rate of dough fermentation

The intensity of bread fermentation is not solely based on a length of time. Despite what many recipes say there are many variables that can cause the dough to not be ready in the timespan expected. Knowing what influences the rate of gas production and fermentation will improve your timing expectations when making bread. Let’s look at the main drivers in gas production:

The amount of active yeast or levain in the dough

The more levain is used in the dough, the faster it can respire to produce gas. This point is not confined to just the amount of yeast or sourdough added to the dough, but the number of active cells they contain.

One sourdough starter might not be as active as another, fresh yeast might not be as fresh and so on. There is also conversion between yeast types that must be accounted for when using a different type than a recipe states.

Instant, active dried and fresh bakers yeast contain differing amounts of active cells.

The dough hydration

Drier, stiffer doughs develop slower. Natural enzymes find it harder to move about in dense dough. Heavily hydrated doughs tend to be faster to start breaking down carbohydrates into simple sugars. When this is considered it becomes obvious why stiff doughs often require extra sugar in the recipe. Yeast is reliant on free water to pass nutrients in and out the dough system, without it, the activity of the yeast slows down.

The use of salt

Salt plays an important part in bread making. Salt has four roles:

  • Enhances the structure of the gluten
  • Slows down the activity of yeast
  • Brings out flavour
  • Adds flavour

Though bread can be made without it, we should add salt for great looking and tasting bread. Salt soaks up free water in the dough making it harder for water and other molecules to flow. This effectively slows down the rate that the yeast can respire. Salt produces a slower proofed and more flavourful bread.

More salt = a slower rise

The amount of sugar

A small amount of table sugar added to the dough recipe will provide a steady stream of food for the yeast. This is ideal for dough which you want to proof quickly. The yeast doesn’t have to wait for starches to be broken down as it has simple sugars available.

But if the dough contains a lot of sugar, the activity of the yeast is hindered. The process of osmosis (described above) is where water is used as a carrier between cells. It’s essential for yeast and the enzymatic reactions to take place in bread dough. But, like salt, sugar soaks up water in bread dough. When there is too much sugar it causes osmotic stress. This is where the yeast is so dehydrated it cannot operate and turns inactive.

The solution is to keep sugar levels below 5% or use a special type of yeast called osmotoeralent yeast. This is a yeast that can operate under high osmotic pressure and is ideal for sweet breads and yeast-leavened cakes.

The quality of the starch in the flour

During the milling process, it’s inevitable that some of the starch particles are going to become damaged. Whilst damaged flour is bad for the structure of the gluten, damaged starch is easier to break down into sugars. This increases the rate of yeast respiration at the beginning of fermentation, similar to how the addition of a little table sugar would.

The amount of amylase in the flour

There are many tests that can be carried out to determine the quality of the flour. One that has the most impact on the rate of fermentation is the amount of amylase present. The rate at which starch can be broken down into sugars is dependent on the number of natural enzymes in the flour. These enzymes such as Amylase (and Maltase) vary between flour types.

The way to determine qualities such as these are Falling Number or Amylograph tests. The cost of these bits of kit means that for most of us we have to learn how our flour reacts from experience.

If you suspect that your flour has a low quota of active amylase you can add activated malt flour to your recipe. Though don’t add too much as it can turn your bread gummy!


Yeast loves warm and humid conditions to thrive. Relative humidity between 50% and 90% is ideal for gas production.


The development of lactic acid bacteria lowers the acidity of the dough during fermentation. The species of yeast used in commercial yeast (Saccharomyces Cerevisiae) and sourdough enjoy operating in slightly acidic environments.

A pH of 4.5–6.5 is typical for yeast-leavened bread, whereas sourdough starters can drop to a pH of 3.0. This is one of the reasons why LAB overpowers the wild yeasts in a mature starter.


By adjusting the fermentation temperature, the availability of simple sugars changes along with yeast activity. We can change the speed of production and the sweetness of the bread by adapting the bread’s proofing temperature and/or the temperature of the dough at the end of mixing called the desired dough temperature.

Yeast is most active when it’s warm. The warmer it gets, the faster it can respire. Until it gets too warm that the yeast cells die. The next section goes into the impact of temperature further during the fermentation of bread.

How to use temperature to control fermentation

The temperature of fermenting dough is a big variable. In a home kitchen, temperatures can fluctuate wildly, which impacts the timing of the rise. It will also affect the flavour and texture of the bread. Skilled bakers can use temperature to not only control the rate of production but to create unique flavours. Though changes in flavour are not controlled by the yeast but by the enzymes it produces.

The impact temperature has on enzymes

First off, let’s discuss cool fermentation. Maltase is the primary enzyme produced by the yeast. It is used to break down the most prevalent disaccharide, maltose into glucose and operates best at 40C (104F). At 25C (77F) its activity drops off and it struggles to supply the yeast with enough glucose for glycolysis.

Whilst yeast prefers warmer conditions to respire, it can still do so at cooler temperatures, say between 18-25C (65-77F). However, as the sugar supply is reduced it will simply run out of sugar to respire. Another enzyme, invertase prefers even warmer temperatures as it is most effective at 60C (140F).

This makes the fermentation or proofing of bread below 25C (77F) associated with poor quality bread. Or does it?

Well no, hmmm, not exactly anyway! Complex sugars can still be broken down by enzymes such as maltase and invertase at cooler temperatures. It just occurs at much slower rates.

Cool fermentation

If dough is placed in the fridge to bulk ferment, its temperature will drop so that it is too cold for the yeast to respire. Yet, simple sugars are still produced.

When dough is left in the fridge overnight (which is typical for artisan and sourdough bread) monosaccharides are still produced. Yet these will remain unfermented as it’s too cold for the yeast to operate.

Once removed from the fridge to proof on the counter, or baked straight from cold, there is an abundance of sugar available for the yeast. As fermentation ends in the oven, any remaining simple sugars sweeten the bread.

The process can be reversed when a 50-75% proofed loaf can finish off its rise in the fridge where it will develop more simple sugars. This makes it taste sweeter and provides plenty of “food” for the oven spring.

Warm fermentation

Just as cool fermentation increases the flavour of bread, a warmer bread proofing temperature can also alter flavour characteristics. As discussed in this article discussing how to make sourdough bread more sour, the proofing temperature has an impact on the acids produced. Acetic acid is produced at around 35C (95F), whereas lactic acid is more prevalent at circa 25C (77F).

The heterofermentative fermentation produces acetic acid and also  CO2. Thus, proofing warm dough can introduce slight vinegary notes and also rise quicker.

Proofing dough above 35C (95F) also sees a rise in enzyme activity. This again produces more simple sugars to supply the yeast or sweeten the bread.

The flavour can be further tweaked by adjusting the proofing temperature to target a particular enzyme. This is most challenging for home bakers without a home proofer but common for professionals.

The impact of fermentation time and flavour in the bread

As the dough ferments, it becomes more acidic due to lactic acid fermentation. As the pH value of the dough drops below 5.0, maltase becomes much less effective and produces fewer monosaccharides.

Invertase on the other hand can cope with a pH of 4.0. This means that when the dough reaches this acidity it takes over the “breaking down” of disaccharides and instead of producing solely glucose, the output of the invertase enzyme is one glucose and one fructose molecule.

Fructose produces a sweeter flavour so longer-fermented bread dough will taste slightly sweeter.

Avoiding the middle ground

As a bread bakers, we want to avoid the middle ground. If a lighter tasting loaf is expected, (ideal for sandwiches) we should try to achieve a faster rise. This will be produced through the yeast aerobically respiring and fermenting less. Or at least, fermenting at a high temperature so the heterofermentative reaction can also produce gas. To maximise aerobic respiration the bulk fermentation step is short or skipped entirely.

For fuller-flavour artisan bread, allowing the yeast to ferment in cooler environments develops more flavour in the bread. The flavour will come from the ethanol, organic acids and expect some added sweetness from the breaking down of the starch.

The ideal temperature for fermenting artisan bread is circa 24-28C (75-82F). Too warm and the dough will rise too quickly and miss out on these fantastic flavours. Less oxygen should also be incorporated as anaerobic respiration will provide more oxygen and an extended maturation period can cause over-oxidising the flour.

When getting artisan bread right, the result is a bread that is full of flavour, not so sweet – but not necessarily inferior. For more enhancement, the dough can be placed in the fridge for bulk fermentation or proofing.

The temperature range to avoid when fermenting bread

What we should try to avoid in most cases is proofing the dough between 10-24C (50-75F). This is the middle ground and sees neither benefit from advanced gas production nor flavour development.

Getting the balance between gluten development and the type of respiration intended is also defining to produce quality bread.

Bread that is made quickly can easily run out of oxygen or sugars and switch to anaerobic respiration. Also, if a quickly-made loaf has been under-kneaded it won’t be able to retain the gas in the dough effectively and the bread turns out flat or dense.

What happens if dough gets too warm?

Yeast prefers it warm, it will continue to increase its rate of respiration up until it dies. But as you may be aware, we don’t proof bread above 40C (104F). The enzymatic process of breaking down the disaccharides into monosaccharides isn’t able to keep up demand from the yeast.

The gluten structure also requires time to mature and stretch. Proofing dough too warm or with too much yeast produces more water as anaerobic respiration increases. An excessive amount of water can be too much for the flour to absorb at the rate required. This produces a wet and weak dough.

The impact of gluten on yeast fermentation

The development of the gluten structure, whilst not a part of yeast fermentation should also be considered when determining the fermentation duration or intensity of bread dough. How and why are explained below.

How gluten appears in bread

When water hydrates starch to begin the enzymatic changes required for producing pyruvates for the yeast, it also hydrates the protein. Now, there’s much to be said about protein content in bread making, with the topic of how much protein flour should contain to make bread a popular topic. Let me explain some of the basics.

Hydrated protein in flour changes into gluten. The gluten strands are initially coiled up and tangled with each other. As they hydrate they become stronger and become more straight and less messed up. As they straighten the gluten strands become extremely long and bond to each other in a less irregular pattern than before. This produces a gluten structure, sometimes called a matrix.

The number of bonds, the type of bonds and the distance between them can be altered by the kneading technique and the ingredients in the dough.

How fermentation improves gluten

The benefits of an extended fermentation period are super cool for the gluten. Aside from the flavour and keeping quality benefits, ethanol and organic acids aid the extensibility and elasticity of the dough. This is great for shaping and handling the dough and also improves the glutens ability to retain gas.

This is why you will often see an extensive list of dough improvers on the ingredients list of store-bought bread. Long fermentation of bread is more costly. Commercial bakers often add an oxidizing agent such as ascorbic acid to improve the bonding of the gluten. Other additives and enzymes are also added which replicate the benefits of a long-fermented dough.

What type of flour can be used for bread?

When it comes to making quickly-made bread, gluten misses some of the structural benefits of long fermentation. For this reason, these doughs need as much gluten as possible to retain the gas produced, therefore a high-protein flour is selected.

The flour is often further enhanced at home by adding vital wheat gluten or alternative protein such as eggs. Though the protein found in eggs is different to gluten, they still add strength to the dough and aid the rise.

But gluten content is not all about the protein content. Like starch, during the milling process, some of the proteins can become damaged and split. This means that once the flour is hydrated, despite containing lots of protein, it might not be in the best shape for retaining gas. Not right away at least.

Over time, hydrated damaged protein recovers and repairs itself. This means that flour with a high ratio of damaged protein can be used to make fermented bread dough. But for quickly made bread, this isn’t good enough!

Damaged flour is poor flour and not good enough for making quickly-made bread and rolls. Some bakers will often add vital wheat gluten to their flour. This ensures that there is enough protein to produce a quality loaf. It’s a fantastic way to remove the problem and guarantee results, yet I’d rather focus on finding a quality high-protein flour and only using vital wheat gluten as a last resort.

When making longer proofed bread, it’s possible to use flour with less protein content. Due to the ability of damaged protein particles to repair themselves over time, bread flours or all-purpose flours with a protein content of around 11% are suitable for making artisan bread. The quality of the flour is still important though, generally if it smells nice and aromatic it has been well grown and treated during processing.

There are of course much more scientific tests into the quality of flour which home bakers and the majority of small bakeries are unable to conduct. For example, some flours aren’t able to withstand long fermentation, they collapse. Others can’t stretch as well and some may contain less active enzymes such as amylase.

There are little cheats and extra ingredients that can be added to the flour to compensate for these issues. But please don’t go down the route of – because someone adds malt flour to their recipe that you must do the same. What works with their ingredients, environment and recipe may work perfectly for them, but not for you.

Benefits of cold fermentation on gluten

Cold fermentation in the fridge assists broken protein particles to repair. This is because gluten hydrates and bonds at cold temperatures which reinforces the strength of the structure. It also increases the ability of low protein flour to be used for bread.

More kneading vs long fermentation – what is better?

Kneading more vigorously encourages oxygen to be incorporated to oxidise the flour. This adds strength to the gluten bonds and as we now know is vital in the aerobic respiration of the yeast. Over time, dough left to sit out oxidises naturally. But when oxygen levels rise too much, the oxygen bleaches the carotenoid pigments in the flour causing a lack of colour, flavour and aroma.

This means we don’t want to knead a long-fermented dough too much. A light incorporation with further agitation by stretch and folds is preferred.

The impact of stretch and folds

Stretch and folds are used in medium and long-fermented bread doughs. They are a method to develop gluten strength whilst redistributing the ingredients in the dough to increase the rate of yeast fermentation. There are many methods to stretch and fold, which vary in their effectiveness to stretch gluten and the time required to do so.

When stretching the dough you are able to match the gluten development with its fermentation level. If you notice your dough is getting gassy, use a more aggressive stretch and fold method and do it more regularly. If the dough is under fermented but the gluten is long, elastic and passes the windowpane test, a gentler stretch and fold method is preferred.

Conclusion: Is fermentation important to bake bread?

It’s a fantastic process and yes, fermentation is absolutely important in making bread. The ability to correctly ferment the dough without under or over-fermenting is a challenge that many beginner bakers struggle with.

Follow a good recipe from a reliable source and taking regular temperature checks is key, but use a simple recipe such as my beginner’s bread recipe. It’s a confusing topic to describe so well done for reading this far! Let me know in the comments below if you found this useful and to ask any questions.

Further reading

I have used these books as references for this article. To learn more about the science in baking bread you should check them out:

Bread Science: The Chemistry and Craft of Making Bread – Emily Buehler

The taste of bread – Raymond Calvel

Additional references:




Frequently asked questions about fermentation

What is the perfect fermentation temperature for artisan bread?

Artisan bakers typically operate the first rise at 24-28C (75-82F), but the second rise can vary. A 32C (90F) final proof is possible, whereas cooler temperatures are acceptable, including an overnight rise in the fridge.

Is bench rest fermentation?

Fermentation does not pause whilst the dough is bench rested between preshaping and final shaping. Though the bench rests role is to allow the dough to relax. Its length is determined by the strength of the gluten and so is not categorised as a fermentation stage.

Why does bread stop rising in the oven?

  • The yeast gets too hot and dies
  • The crust hardens preventing the loaf from rising
  • The yeast runs out of simple sugars

Is yeast fermentation the same as dough fermentation?

Yeast is the strain that initiates fermentation in the dough with carbohydrates. Dough does not ferment, the yeast does. Both phrases are used interchangeably in bread baking.

Where does yeast consume the sugars?

In aerobic respiration the consumption of sugars into carbon dioxide, water and HTP occurs inside the yeast cell. Anaerobic respiration can take place inside or outside the cell walls.

What is the difference between yeast fermentation vs respiration?

Yeast has to respire before it can ferment. It can do this with or without oxygen. In the case of aerobic respiration, there is no fermentation. When yeast respires anaerobically, both alcoholic fermentation and lactic acid fermentation occur.

Are organic acids good for bread dough?

They help in the production of the bread as its machinability improves, has a bigger rise, a bigger oven spring, lighter crumb, tastes, smells and looks more interesting and keeps fresh for longer. All quite important.

Is Zymase used in dough fermentation?

It was thought that the enzyme, zymase kick starts yeast fermentation. It occurs from yeast and turns the monosaccharides, glucose and fructose, into carbon dioxide and ethanol. This has been refuted by experts in recent years.

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  1. That is a great tip.

    Simple but very accurate info… Thanks for sharing this one.
    A must read article!

  2. There’s so much info in your article that it’s mind blowing.
    I’m a simple bread baker been doing it commercially for the last 2 or so years. If l read
    your article at the beginning l think l would not have even started.
    There’s so much to take in, talk about comprehensive.
    I was interested in the proofing temperatures thou. Great article.

  3. Thank you Chris. You don’t need to know all of this to have the best bread in town. Good ingredients and good technique are just as important. Glad you found some insight!

  4. Very good article! It takes time to put together a thorough paper like that.

    I do have one question.

    Under Three ways for fermentation, 2- Fermentation to produce lactic acids. You state “Aside from yeast respiration, the enzymes in the dough also break down carbohydrates to produce Lactic Acid Bacteria (LAB).”

    Maybe I am not understanding the way you state this but as it reads to me you are stating that yeast thru enzymatic action is creating ( you use the word “produce”) lactic acid bacteria which then produces lactic acid. If my understanding of what you have written is correct I would have to ask how thru what process enzymes are creating/producing bacteria. The bacteria is fed by the enzymes converted output and the bacteria produces lactic acid but the enzyme does not somehow create a single cell organism. As in create life from an enzyme.

    At its basic definition enzymes are large molecules, mostly proteins, that speed up chemical reactions. They act upon substrate. But enzymes are not living organisms. But living cells of an organism can and do produce enzymes as part of energy production and waste removal.
    Bacteria on the other had are one-celled living organisms that require food and produce enzymes.
    Thus yeast breaks down energy molecules thru enzymatic action to make a compound that the lactic acid producing bacteria usually in the case of flour from the genus lactobacilli. Point being yeast is not a creator or progenitor of bacteria its a produces of substrate thru enzymatic action that feeds bacteria already present be it from inculcate in the field or bakery or both.

    So LAB are already present and yeast feed them.

    Again a great writeup and not trying to nit pick just want to be clear. I can accept I miss read what was being conveyed. You just did such a great job explaining the science which so many home bakers have very little knowledge, did not want there to be an error where people are thinking yeast enzymes are birthing bacteria.

  5. Fantastic comment, thank you. I love this type of comment! I’ll update the post to make it clearer/accurate 🙂

  6. Hi Gareth, I recently discovered your website and have been reading your articles with great interest. I’m a home baker who has been baking bread for two years and love reading articles like this to improve the way I bake.

    You state that bulk fermentation should be carried out at either high or low temperatures, while the middle ground (10-24C) should be avoided. However, I don’t quite understand why one can’t use the middle ground to create a sandwich loaf (for example) that has a slightly longer fermentation time and slightly more flavour than a fast-rise loaf.

    Also, I’ve been experimenting with reducing the amount of yeast I use (rather than the temperature) to lengthen fermentation times. How do the two approaches compare in terms of the end result (crumb texture, rise, etc.) in your view? The breads I have baked using reduced yeast (bulk fermenting to the same volume as when using the full amount of yeast) seem inferior, but I can’t figure out why this would be. Surely, reducing yeast just means that additional time is needed for the yeast to multiply to get up to par, but once that point has been reached, the dough should behave in the same way as using the full amount of yeast to start off with, no? I would really appreciate any light you could throw on this. Thank you.

  7. Hi Jee! Thanks for your questions. Let me answer, “why not proof at 10-24C” first.

    The overarching reason is that there is no point to (in my opinion). Yeast is able to operate in this temperature range, albeit at a slower rate than if it was warm. The reason why I don’t recommend it is the enzymes that break down starch into sugars slow down in this temperature range. Once the readily available sugars are consumed the yeast has less food for respiration and the rise slows down. So it’s not that this has to be avoided at all costs, it’s just that there is a better way.

    If you want a sweet, mature flavour, either use a preferment or pop the dough in the fridge overnight. You’ll get more gluten maturity, sweeter flavours and an abundance of simple sugars (instead of enzymes, the starch breaks down slowly through hydrolysis) that will boost the rise once the temperature of the dough warms up. And if you want a lighter-tasting bread, ferment it warmer.

    So yeah, you could proof at say 20C and get a slower rise, but I’d rather proof at 25C and use slightly less yeast so I get the same slow rise but in better conditions for the yeast. This, in theory, should increase flavour and fermentation benefits.
    It makes sense based on the science papers that I have studied. It’s hard to control dough temperature at home so whilst this all makes sense in theory, proofing below 25C is common and you can still make great bread by doing so.

    To answer your second question regarding lowering the yeast:

    During bulk fermentation you are balancing 3 main things:
    – Gas production
    – Gluten development
    – Oxygen levels
    If the dough is left for longer it will build strong gluten bonds, yet it will also absorb more oxygen. I urge you to read this oxidation in bread post. It explains how oxygen is good initially for dough, but bad as fermentation duration extends.

    So by leaving the dough for longer, regardless of using less yeast you can end up with some of these features:
    -Protease enzyme weakening the gluten
    -Gluten becoming naturally stronger
    -Lactic acid levels increase which weakens the gluten at excessive levels

    So yeah, your findings are correct, the dough will behave differently! A solution to this is to knead the dough less when extending fermentation time. This reduces oxygen absorption and gluten development.

    Hope this makes sense!

  8. Wow, thanks for such a detailed answer! It’s really helped me to understand things better. Jee

  9. this is an excellent expose on how the development of bread works. I found it by trying to find the “real” reason whole wheat flour ferments faster than white flour. My supposition is that whole wheat has more enzymatic action in it breaking down starch to sugars because there is NOT more starch (which needs to break down to sugar to feed the yeast) per se in whole wheat. Seems like there would be LESS food for years in same weight of whole grain vs white flour. So I’m thinking it must be enzyme. One site says there is MORE nutrients in whole wheat. But I have yet to find where yeast needs anything BUT sugar to ferment. Any thoughts on all this? thanks!

  10. Thank you Thomas! In my experience, whole wheat isn’t always faster to ferment than white flour. If there is malted barley (malt flour) added to the whole wheat then this speeds up the enzymatic reactions. One of the key differents in the rate of fermentation is the amount of starch in the flour that is damaged. Only damaged starch is initially broken down by the Amylase enzyme. It’s possible that your whole wheat flour has a lot of damaged starch, especially if the flour is stoneground.
    Whole wheat flour has more bran and germ which contain nutrients. These nutrients provide more bacteria to be broken down by enzymes. This produces a slower, but higher rise and is especially handy for sourdough starters. Some of these nutrients will contain hexose sugars which can be fermented by the yeast, but the bulk of gas production is through the yeast respiring on broken down starch and sugars.

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