What Does Yeast Do To Bread? Bread Fermentation Process

Bread fermentation process
Published on
20 October 2020
Gareth Busby
Gareth Busby

The bread fermentation process is the science behind flour, water, salt and yeast coming together to produce a dough that’s ready for the oven. This article reveals how important dough fermentation is whilst deep diving 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!

Just a disclaimer before we continue: this article is designed for a hardened bread baker. If you’re a beginner then this detailed guide might alienate you! You can still make great bread without this knowledge, but you’ll be able to make better loaves with it.

Knowing the science behind baking bread allows you to cut through the bad advice and make better choices. After reading this guide you’ll know how bread fermentation works and its importance in making quality bread. You’ll also understand how flour adapts during the bread-making process to provide food for the yeast and develop the gluten structure, plus plenty more!

What is fermentation?

Fermentation comes from the Latin word “Fermentare”, meaning “to leaven.” It is a vital stage in foods such as cheese, yoghurt, alcohol, pickled foods and bread. For fermentation to occur, a base and a strain are required. The base is a carbohydrate, and the strain will be bacteria or a fungus. In bread fermentation, the base is the carbohydrates in the flour, and the strain is the fungus, yeast.

Bread fermentation simplified

As soon as yeast comes into contact with flour and water, the yeast fermentation process begins. Hydrated carbohydrates break down into simple sugars by enzymes and natural hydrolysis. These sugars supply the yeast with food for it to respire, aerobically or anaerobically. Carbon dioxide is the product most associated with yeast respiration to make bread. The CO2 produces fills pockets of air in the gluten and as the pockets (alveoli) expand, the bread rises.

Alcoholic fermentation, instigated by yeast, alongside homofermentative and heterofermentative bacteria, generates other components. These include ethanol, lactic acid, acetic acid, plus various other compounds. How this happens and how to control the balance between fermentation vs solely carbon dioxide production take a bit of effort to understand. But no need to worry, you’re in the right place! Let’s bring it back a bit and start with what yeast is and how yeast works in bread.

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 bread levain has been traced back to ancient Egyptians and beyond. A sourdough starter is a culture containing multiple yeasts and acid bacteria. To find out more about how sourdough works, check out my sourdough fermentation process article.

Yeast and sourdough

Back to yeast… There are 1,500 types of yeast, and each version has a multitude of strains. The type of yeast used in all types of bread is Saccharomyces Cerevisiae. This yeast is also found in sourdough starters and alternative strains of Saccharomyces Cerevisiae are also used to ferment beer.

In the case of active dried and instant dried yeast, the yeast cells are dormant until hydrated with warm water. Fresh (bakers) yeast contains a much higher ratio of water and is active. It is kept “alive” by keeping it cold in the fridge. At cool temperatures, yeast activity is lowered without damaging the cells. More on this later.

How sugars are supplied to the yeast

Carbohydrates make up around 60-70% of bread flour. There are three categories of carbohydrates; simple sugars, starch and dietary fibres. Each is composed of the same simple sugar molecules, but take on different forms through molecule combinations and the size of the chains.

Simple sugars

Simple sugars are the simplest form of carbohydrates. They consist of single-cell monosaccharides and double-cell, disaccharides. As part of the human digestive system, these sugars need little breaking down to be absorbed through cell walls and are quickly absorbed into our bloodstream. This means that they provide quick bursts of energy. Though if all the energy from a sugary snack is not utilised it is not great for our body.

Glucose, fructose and galactose are monosaccharides with 6 carbon atoms called hexoses. These are the monosaccharides that are primarily used by the yeast. maltose, sucrose (table sugar) are disaccharides that are formed by bonding monosaccharides. The main sugars in flour are glucose, fructose, sucrose and maltose. Not all of these sugars taste sweet.

Starch

Starch is produced by vegetables to store energy. These are more complex carbohydrates, formed of monosaccharides and disaccharides connected by glycosidic bonds. Starches (polysaccharides) are broken down in the dough to become simple sugars. Without breaking down the bonds, a starch’s complex make-up means it doesn’t have a sweet flavour. 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 outer casing of the wheat germ and the largest source of dietary fibre in bread. This makes white flour, which has a majority of the bran removed less good for you.

The enzymatic action of yeast

There are some simple sugars available in flour, but to produce enough for the yeast to make enough carbon dioxide the starch and fibre chains must be broken down into disaccharides. The starch will naturally break down when moist and in the presence of acid. This process is called hydrolysis and is noticed primarily when bread dough is left to ferment in the refrigerator. It’s a slow process but unlike enzymes, it continues to process starch even at cool temperatures.

To accelerate the simplifying of the starch, dough utilises enzymes. These are either added as an ingredient, produced by the yeast or naturally occurring in the flour:

  • Amylase breaks down starch into the disaccharide, maltose into two bonded glucose molecules.
  • Maltose is broken down by the maltase enzyme to leave two glucose sugars.
  • Another enzyme, invertase, breaks down a disaccharide called sucrose (table sugar) into two monosaccharides, glucose and fructose.

The glycolysis process

Monosaccharides are still too large to penetrate the yeast cell walls. Instead, in yeast respiration (yeast respiration comes before fermentation), glucose cells undergo a process called Glycolysis.

glycolysis pathway
Source: https://courses.lumenlearning.com/suny-biology1/chapter/glycolysis/

Here a glucose cell is broken down through a chain of reactions into two pyruvates whilst releasing energy (ATP- Adenosine Triphosphate). Once From here there are two possible outputs.

Aerobic respiration vs Anaerobic respiration

As the simple sugars undergo glycolysis. The pyruvates produced are supplied to the yeast either with or without the presence of oxygen. This produces aerobic, or anaerobic respiration.

Aerobic respiration

The Krebs cycle
https://imedscholar.com/open-blog/biochemistry/tricarboxylic-acid-cycle-krebs-cycle/

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

C6H12O6  +  6O2  →  6CO2  +  6H2O  +  2,900 kJ/mol (36 ATP)

* C6H12O6 is a Pyruvate

Carbon dioxide doesn’t appear as a gas at first. It begins as a liquid and travels through the gluten structure to a point of low pressure where it is released as vapour.

Anaerobic respiration

The output of anaerobic respiration leads to alcohol fermentation. Without oxygen, the pyruvate does not enter the complete Krebs cycle. Instead, the pyruvate latches to an inorganic phosphate. NAD+ produced at the end of glycolysis gains a hydrogen atom to produce NADH. The enzyme, pyruvate decarboxylase catalyses the release of CO2, and in the presence of alcohol dehydrogenase (produced by baker’s yeast), ethanol (alcohol) is produced. 

C6H12O6  →  2C2H5OH  +  2CO2  + 118 kJ/mol (2 ATP)

* 2C2H5OH is Ethanol

Aerobic respiration produces much more energy than fermentation. This means gas production occurs faster when oxygen is present in the dough.

Aerobic vs anaerobic respiration

Aerobic respiration vs fermentation
https://www.singerinstruments.com/resource/what-is-yeast/

Aside from yeast respiration, bread dough can also ferment with acidic bacteria. Lactic Acid Bacteria (LAB) are found all around, such as in flour and the environment. As dough matures, the bacteria multiply.

Similar to yeast strains, there are many species of lactic acid. Lactobacillus Casei is a common one that’s found in breadmaking. Three categories of LAB exist; Obligate homofermentative, Obligate heterofermentative and Facultative heterofermentative:

Obligate homofermentative

Homofermentative bacteria fermentation is similar to alcoholic fermentation. Instead of ethanol, the pyruvates produce lactate molecules in the presence of the enzyme Lactate Dehydrogenase. Lactate is easily converted to lactic acid.

Obligate heterofermentative

10% of LAB is heterofermentative. This means simple sugars follow the Phosphoketolase pathway. The glucose molecule, instead of being split into two pyruvates, produces one pyruvate and one acetyl-phosphate. The pyruvate will become lactate, whereas the acetyl-phosphate molecule will either become acetate or ethanol. This process also releases CO2.

Similar to lactate, acetate leads to acetic acid. Acetic acid is the key component of vinegar. A popular heterofermentative bacteria you might have heard of is Lactobacillus Sanfranciscensis (now called, Fructilactobacillus Sanfranciscensis). This is a core feature of the sourdough bread made in San Franciso but found in many other places too. Other acids are also produced and categorised as “various organic acids”.

Facultative heterofermentative

Facultative heterofermentative lactic bacteria have the ability to switch between homofermentative and heterofermentative processes.

All fermentation routes that occur have some similar traits:

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

When do lactic and acetic acids occur in yeasted bread?

The use of organic acids is at the forefront of sourdough baking, and in fact, I go into even more detail about these processes on the sourdough fermentation page! The difference in the treatment of acid bacteria in sourdough and yeasted bread is that it is responsible for approximately half of the CO2 produced in sourdough bread. In yeasted bread, they do occur but have minimal effect in quick-bread doughs, where aerobic respiration is the primary reason for the rise.

In longer fermented yeasted doughs, on ones that contain prefermented flour (see preferment guide), organic acids have more of an effect. In these cases, less oxygen is attributed to the dough and therefore fermentation routes prevail over respiration. Let’s discuss the impact organic acids such as lactic and acetic acid have on the dough, next.

The benefits of organic acids produced in bread

Organic acids change the physical properties of the dough in many ways. They are essential for the dough 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.

Is ethanol needed in bread dough?

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

Is oxygen good for bread?

Oxygen is mostly incorporated during kneading. After kneading it will continue to draw in oxygen from the environment, but at a much lower rate. If a more aggressive kneading technique is used, more oxygen is incorporated. If 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 good time to highlight how a dough with low sugar content can also cause anaerobic respiration to take over. It often happens when making whole wheat dough. Whole wheat flour needs more time to hydrate in order for the starch to break down. This leads to a bitter aroma that doesn’t couple well with the hearty smells of whole grain wheat. To counteract the bitterness table sugar is often added. Although soaking some (or all) of the flour in the form of an autolyse, soaker or preferment can also be used.

As more energy is produced during aerobic fermentation, the dough rises faster. For quick-breads, introducing oxygen via kneading aggressively is vital.

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

Bread has a lighter flavour and a soft texture.
The 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, and 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 dough’s original size.
ProofingAfter shaping, the dough is proofed for the final time. As time goes on, the process of enzymatic and fermentation activity continues 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 overproof 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 basic recipes say, many variables cause the dough to 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 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 baker’s yeast contain differing amounts of active cells.

The dough hydration

Dry, stiff doughs develop slower. Yeast and enzymes find it harder to move about when there isn’t much free water. Heavily hydrated doughs tend to be faster at breaking down carbohydrates. When this is considered, it becomes obvious why stiff doughs often include more sugar in recipes. Yeast is reliant on free water to pass nutrients in and out of 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

Bread can be made without salt yet we should still add it for great-looking and tasting bread. One of the key benefits of salt is that it soaks up water in the dough. This makes it harder for molecules to flow and slows the rate at which yeast operates. Salt produces a slower-proofed and more flavourful bread.

The amount of sugar

A small amount of table sugar in a dough recipe will provide a steady stream of food for the yeast. This is ideal if you want to prove it 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 is where water is used as a carrier between cells. It’s essential for yeast and 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 in sweetened loaves. This yeast can operate under high osmotic pressure and is perfect for sweet bread 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 damaged. Whilst damaged flour is bad for the structure of the dough, it is easier for the enzyme, amylase to break down starch into sugars. This increases the rate of yeast respiration at the beginning of fermentation, similar to a little table sugar.

The amount of amylase in the flour

There are many tests that can be carried out to determine the quality of the flour. The rate 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 (malted barley). Don’t add too much though, it will make your bread gummy!

Humidity

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

Acidity

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. When the dough is overly acidic, yeast activity slows down. This is why LAB overpowers the wild yeasts in a mature sourdough starter.

Temperature

By adjusting the fermentation temperature, the rate at which enzymes break down starch into simple sugars changes. Also, different enzymes operate at different temperatures which alter the flavour of the bread. In warm temperatures yeast activity increases.

Therefore we can change the speed of production and the flavour 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. The next section explains the impact of temperature during yeast fermentation.

How to use temperature to control fermentation

Skilled bakers use temperature to not only control the rate of production but to create unique flavours. Changes in flavour are not necessarily controlled by the yeast, but by the enzymes produced.

The impact temperature has on enzymes

First, let’s discuss cool fermentation. Maltase is the primary enzyme that’s 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 maltase activity slows, the sugar supply is reduced and the yeast simply runs out of sugar to produce gas. Another enzyme, invertase prefers even warmer temperatures and 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 at cooler temperatures by enzymes, or with natural hydrolysis. It just occurs at a much slower rate.

Cool fermentation

If dough is placed in the fridge to bulk ferment, its temperature will drop so low that the yeast becomes dormant. Yet, simple sugars are still produced through hydrolysis. Often artisan or sourdough bread dough is left in the fridge overnight. During this cool fermentation, monosaccharides are still produced albeit at a slower rate. These sugars remain unfermented until the dough gets warm. This will either be when baking straight from the fridge or left proof first on the countertop. There will be an abundance of sugar for the yeast, often causing a rapid rise. As gas production ends in the oven, remaining simple sugars can contribute to the sweetness of the bread or caramelisation of the crust.

A common technique is to place a 50-75% proofed loaf in the fridge for the remainder of its rise. Here, the fridge takes time to cool the dough therefore it continues to rise for 1-2 hours. The dough can then sit in the fridge further where it will develop more sugar. This makes it taste sweeter and can be consumed during oven spring for a larger growth. There are also enhancements for the gluten when using cool fermentation techniques, which we’ll return to shortly.

Warm fermentation

Just as cool fermentation increases the flavour of the bread, a warmer 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. Lactic acid is produced at around 35C (95F), whereas Acetic acid is more prevalent at cooler temperatures, circa 25C (77F).

Proofing dough above 35C (95F) also sees a rise in enzyme activity. This again produces more simple sugars to supply the yeast and sweeten the bread. Commercial bakeries often use the Chorleywood method to produce bread quickly with yeast respiration favoured over fermentation. Because of a lack of organic acids produced, dough improvers and enzymes are added. To make the flavour of the bread more interesting, the dough is proofed at 38C (100F). This temperature allows enzymes to flourish and add a natural sweetness that would not be realised at a 32 or 35C (90-95F) proofing temperature.

Folding Proofer & Slow Cooker

Bread flavour can be tweaked by adjusting the proofing temperature to target particular enzymes. This is most challenging for home bakers without a home proofer but common in commercial baking. If you would like to experiment with proofing temperatures at home you really need to get the Brod & Taylor home proofer. It allows you to set your temperature so you can perfect your proofing temperature. Take a look for yourself at the Brod & Taylor.

The impact of acidity in long-fermented bread

As the dough ferments, it becomes more acidic. 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 as low as 4.0. When a long-fermented dough reaches this acidity level, Invertase takes over where it produces one glucose and one fructose molecule instead of solely glucose which would occur when Maltase is the more prevalent enzyme. Fructose produces a sweeter flavour than glucose, therefore longer-fermented bread tastes sweeter.

Avoiding the middle ground in bread production

Take a temperature check of your dough

As 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. To maximise respiration bulk fermentation (first rise) must be short, or skipped altogether.

For fuller-flavour artisan bread, a cool first, and second rise develops more flavour in the bread. The flavour will come from the ethanol, organic acids and added sweetness from the extra starch breaking down.

The ideal temperature for fermenting artisan bread is circa 24-28C (75-82F). If it is warmer than this, the dough will rise too quickly and miss out on these fantastic flavours, too cold and the dough won’t rise and risks over-oxidating the flour. Less oxygen should also be incorporated during kneading if anaerobic respiration/fermentation is the desired pathway.

Dough can be placed in the fridge for bulk fermentation or proofing for flavour and structural enhancements. This must be done alongside ambient, or warmer proofing temperatures to allow the yeast to ferment.

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 defined when producing quality bread. Bread that is made quickly can easily run out of oxygen or sugars and switch to anaerobic respiration. If a quickly-made loaf has been under-kneaded the gluten structure may not be able to retain the gas effectively and the bread turns out flat or dense.

What happens if dough gets too warm?

Yeast will continue to increase its rate of respiration as it warms until it dies at 64C (161F). But we don’t prove bread any higher than 40C (104F). The reason for this is threefold:

  1. The enzymatic process can’t keep up demand for sugars for the yeast
  2. The gluten structure requires time to mature
  3. Proofing dough that is warm accelerates anaerobic respiration which releases water. This produces a wetter dough with a weak structure

The impact of gluten on yeast fermentation

Whilst not a part of yeast fermentation, gluten development should be considered when determining the fermentation duration or intensity of bread dough. When water is added to flour, the carbohydrates (starch) and protein absorb it. We’ve discussed the impact of starch in detail already, but what about the protein?

How gluten appears in bread

Water flushes away soluble protein in the flour to leave insoluble protein, gluten remaining. Gluten is a collective of proteins referring to the glutenin and gliadin proteins. There are other proteins contained within the flour, but in order to build the crumb structure or bread, glutenin and gliadin are the important ones.

Gluten development

Gluten is coiled and tangled up when dry. As the strands hydrate they straighten and bond to each other in a less irregular pattern than before. This produces the gluten matrix. The number of bonds and the distance between them can be altered by the kneading technique and the ingredients in the dough.

How fermentation improves gluten

A long bulk fermentation period is great for 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 gluten’s 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.

Flour protein can be enhanced by adding vital wheat gluten or additional protein such as eggs. Though the protein found in eggs is different to gluten, they still add strength to the dough structure and aid the rise.

But gluten content is not all about 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 not good enough for making quickly-made loaves 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 quality high-protein flour and 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 10-11% are suitable for making artisan bread.

The quality of the flour is still important. If it smells nice and aromatic it has been well grown and treated during processing. Bitter unpleasant smells found in many own-brand flours tend to result in unpleasant bread.

There are more variables to the quality of flour that can be conducted with scientific testing. Some flours aren’t able to withstand long fermentation and 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 “if 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

Dough in fridge

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.

The impact of stretch and folds

Stretch and folds are used in medium and long-fermented bread doughs. They are methods used to develop gluten whilst redistributing the ingredients. This aids the gluten matrix and increases the rate of yeast fermentation respectively. There are many methods to stretch and fold, and each has a different effect.

It’s useful to know a handful of stretch and fold methods. When bulk fermenting you should be looking to match gluten development with gas production. If you notice a dough is getting gassy, a more aggressive stretch and fold routine to speed up gluten development is necessary. 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 make bread?

Yes! Yeast fermentation is an interesting subject that could be written about much further, but well done for reading this far! Below I’ve supplied links to websites that I’ve used to compile this article. Check them out if you want to explore the topic further. Did you find this article useful? Let me know in the comments below and use it to ask any questions about the bread fermentation process.

Further reading

I have used these books as references for this article. To learn more about the science of 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:

https://pediaa.com/difference-between-aerobic-and-anaerobic-respiration/

https://bakerpedia.com/processes/fermentation/

https://academic.oup.com/femsyr/article/4/7/683/512027

Frequently asked questions about fermentation

What is the perfect fermentation temperature for artisan bread?
Artisan bakers typically operate the first rise at 25-28C (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. The 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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Comments (12)

  • 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.

    • 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!

  • 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.

  • 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.

    • 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:
      -Over-oxidation
      -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!

  • Avatar for Thomas Cappiello
    Thomas Cappiello

    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!

    • 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.

  • Heya I’m for the first time here. I found this board and I find It truly useful & it helped me out a lot to understand yeast. I’m hoping to present one thing again and help others as you helped me.

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