How Fermentation works in bread baking?
It’s common to learn to bake without fully understanding how dough fermentation in bread baking actually works. Many home and professional bread bakers learn to follow recipes, make a few tweaks and try new ingredients.
But what they don't know is what you're going to, after reading this post.
What we are covering here is how the ingredients and processes combine to turn a collection of basic ingredients into bread.
How dough adapts during the 15 steps of bread baking is very helpful to know, especially when you run into issues with a recipe or if you wish to create your own recipes.
Fermentation is the core of making bread, it's how flour, salt, water and yeast combine and transform into bread. After reading this full guide you’ll know how fermentation works and how that tweaking common bread making stages leads to some unique characteristics to be created in bread.
I’ve been baking for over a decade but it’s only the past two or three years that I have started to introduce more of this theory stuff into my baking.
And the results have skyrocketed!
Let’s see if we can get your bread baking to improve too...
Fermentation basics explained
Fermentation is a process where larger molecules are broken into smaller molecules through anaerobic respiration. The process of fermentation is used to make many common food products including cheese, yoghurt, alcohol, pickled foods and bread.
It requires a base and a strain, the base is a carbohydrate and a strain is a form of fungi or bacteria.
In bread making the base is flour and the strain is yeast.
For those who need a refresher from biology, anaerobic respiration is an enzymic action by microorganisms. Anaerobic means oxygen is not required. Anaerobic respiration isn’t the only form of fermentation, others make food perish, mature flour and make things mouldy.
What happens during dough fermentation involving yeast?
During the process of dough fermentation, we turn a sticky mess of dough into a well-supported structure, which looks and smells delicious.
It starts with water, flour and yeast.
Once these are combined in the mixing bowl, the fermentation begins. The longer the process continues the effects of it become more powerful.
Hydrated flour develops into gluten. The process of yeast acting on the starches in the flour creates gas. The gas gets trapped between strands of gluten which forms pockets of air.
The air pockets expand which force the dough rise. Larger air pockets make a more open crumb and lighter textured bread.
The creation of lactic and acetic acids condition the dough.
Organic acids create flavour, enhance the dough handling properties and extend the keeping qualities of the bread.
Ethanol produced in the process of creating carbon dioxide gas will largely evaporate when baked though traces remain to support odour, flavour and keeping quality.
Here’s a diagram that shows what happens:
Fermentation continues until the oven halts yeast activity by getting to warm. The threshold temperature for yeast is 60C (140F). As the dough temperature exceeds this threshold the yeast becomes permanently inactive.
Expanding on dough fermentation
There’s plenty more to cover on fermentation if we take a look in more detail at each process,
So that’s just what we are going to do!
Breaking down the flour
Gluten is the insoluble portion of the protein. We find protein in the flour. Bread baking flour contains a higher amount of protein than ordinary cake flour. Water reacts with flour making the protein particles soften. When hydrated, the majority of the proteins turns into gluten strands.
Gluten is visible as the stringy stuff in the dough. As the dough is kneaded the gluten will be more noticeable. It’s what sticks to your hands! The gluten strands form a matrix which the dough uses to retain gas.
For bread to rise it needs a gluten structure to retain gas produced by the yeast. When carbon dioxide is produced it gets locked into small pockets of the gluten matrix.
As the amount of carbon dioxide increases the pockets expand, stretching the gluten to form bubbles in the dough.
The gluten structure of a loaf can be observed by cutting it and inspecting the crumb.
We can make changes in how we handle the dough and the fermentation process to create an open, irregular, or close knit crumb types.
There are two different types of gluten, glutamine and glyadin. Glutamine makes the dough hold its shape and focuses on its elastic qualities. Glyadin allows the dough to stretch, creating enough strength to resist ripping.
A combination of both types of gluten are important when making bread.
High strength protein flour is used to make bread. A strength of 11-13% is usually ideal for most types of bread. The general rule is that the higher the protein, the higher the gluten. So the better gas retaining properties the dough will have.
Poor quality flour will contain broken or low-quality protein. Despite being described as containing high amounts of protein, the quality of the protein might not be good enough to create a decent loaf. This is especially true when making long-fermented artisan products.
Low quality or protein ratio flour will have an irregular crumb.
The use of flours that have protein ratios of 14% plus are to be used with caution. Without following a specific process for these flours, too much gluten will be developed making the bread overly dense. The look of these breads is unappealing.
Selecting a flour to use without checking it with the latest flour testing machinery is a bit of a leap into the unknown. Though these bit of kit are beyond most home and small bakeries budgets.
I always take recommendations from other bread makers before I purchase a new brand of flour.
The action of yeast
Yeast fermentation originates from:
- Sugars that exist in the flour such as glucose, levulose and sucrose
- Maltose created from the breaking down of the starch
Common yeast acts on glucose and levulose directly, providing enzymes to act on others namely, invertase and maltase.
Invertase acts on sucrose while maltase breaks down maltose.
Sucrose is transformed, half into glucose and the remainder into levulose.
Maltose turns into glucose.
Another diastase, zymase, does the work of alcoholic fermentation. It turns both the glucose and levulose into carbon dioxide and ethanol.
Fermentation produces complex organic acids. The acids created in this reaction largely involve lactic and acetic acid. Organic acids change the physical properties of the dough, aid it’s maturation and produces bread-like aromas.
As dough fermentation continues the amount of organic acids in the dough rises. the main benefit from long fermentation periods is the increase of organic acid creation.
If organic acids were not availible in the dough, the bread will not be nice to eat. You can see the benefits of organic acids in this diagram:
Without organic acids, the bread would be unpleasant to eat, lack a good crumb structure and be pale in colour - similar to supermarket bread. Bread made commercially which is often sliced has a short fermentation time. The bulk fermentation stage is completely removed in many commercial breads.
To artificially re-create the organic acids that are created over fermentation enzymes and conditioners are added to the dough in the form of dough concentrates or a dough improver mix. The addition of dough improvers or concentrates increases the amount of organic acid productivity, making the bread more palatable.
Lactic acid is an important feature of sourdough though it is found in yeasted breads too. This organic acid lowers the ph value of the dough which generates many benefits to the dough.
Popular benefits of lactic acid are dough maturation and flavour, though the diagram below shows plenty of others. As the dough lowers its Ph value it causes a drop in its extensibility. When dough is over oxygenated has lost too much extensibility it is likely to collapse and spreading out when it gets turned out of the banneton.
Though not mentioned in the diagram, salt does have an important part to play in making bread. Salt supports the structure of the bread, slows down the activity of the yeast and enhances the flavour.
It does this by reducing the amount of oxygenation of the flour. We cover oxygenation in more detail further on in this article.
The stages of fermentation
Fermentation covers 5 stages:
Combination of ingredients
All of these steps are stages of fermentation. It continues until the heat ends the process in the oven.
Let’s focus on kneading first.
Bashing the dough on a table or a mixer accelerates the process of fermentation in bread baking. The aim of mixing is to create a smooth cohesive dough that pulls away at the sides of the mixer. The gluten should develop into a strong structure ready to retain gas during further fermentation.
Most modern bakers follow a two-stage mixing process. The first, slow stage gently hydrates the flour and softens the gluten. Soft gluten is able to stretch and retain bigger air bubbles.
Softer, more hydrated dough is able to stretch larger to create bigger air pockets and a more open crumb.
The fast knead that follows develops gluten and oxygenates the flour. Fast mixing is the only way to form a fine gluten film.
You may notice the glossy, gluten film when mixing the dough. It links the proteins and the wheat germ oils which makes the dough smoother and more cohesive.
Gluten film is also visible as the thin layers of shinny gluten when testing the dough with the windowpane test.
The kinetic action of kneading warms the dough to a more ideal temperature for bulk fermentation. We cover fermentation temperature a bit lower down.
What doesn’t get accelerated is alcoholic fermentation and the creation of acids. These come after time or by using artificial additives.
Even after intense kneading, the dough still needs to mature in able for it to be strong enough to contain a healthy amount of gas.
Oxygenation is the effect when oxygen is absorbed into the flour. This happens whenever the dough is in contact with air and this happens more rapidly when mixing, especially high-intensity mixing.
In small amounts, oxygenation makes the dough stronger and is necessary for making good bread. Over oxidised dough loses its yellow/creamy lipids and becomes a purer white colour which may look attractive at first but it means a lot of flavour is also lost.
Flour oxygenation increases with long, intense mixing, mixing at dough temperatures between 26-27C (75-77F), excessive fermentation, or by delaying the salt till the end of mixing.
It’s also a good idea to cover your dough and use small containers during bulk fermentation to reduce the oxygen it may come in contact with.
Sadly, it’s easily done. The way oxygenation is prevented in commercial bakeries is by using specialist mixers to remove oxygen in the mixing bowl and/or by adding enzymes to condition it.
Oxygenation has one of most important influences in how fermentation works in bread baking.
During the bulk fermentation or what is often called the first fermentation stage, lactic and acetic acid are generated. The amounts of these acids increase over the time of fermentation. There are a few other acids created in this period, but lactic and acetic are the main ones.
Acids generate flavour and mature the dough so that it has better gas retaining and handling properties. They also lower the acidity of the dough (ph value) which aids keeping quality and flavour notes.
Deciding how long to bulk ferment a dough is hard, there is no perfect answer. As dough ferments, it develops the maturation qualities previously discussed however, over fermenting a dough does lead to issues.
Over fermented bread dough
Sometimes, we go out on our canoe and get caught in a tidal drift whilst our dough is left fermenting at home. On return, we’re simply too late. The dough is gassy, full of uneven bubbles and collapses with the slightest touch.
(yes, that happened)
Over fermented flour has had too much exposure to oxygen, diminishing the flavour of the bread and making it bitter. The yeast will have eaten all the sugars it could find and burn out, refusing to ferment any further with as much gusto as usual.
Over fermented dough is too gassy to mould properly. A weak, uneven crumb structure is common. It tends to have a strong whiff of alcohol. Extra unwanted ethanol is created and remains after the bread is baked.
If the dough is over fermented I recommend baking it straight away straight on a baking stone without shaping. Hopefully, you will end up with a rustic style bread similar to a campaillou.
How long to bulk ferment bread dough
Many factors affect the bulk fermentation duration. The main factors to determine the length of bulk fermentation are:
- The humidity and temperature of the room
- The water content
- Dough temperature
- Length of mixing
- Oxygenation levels
- Yeast amount used
- Amount of salt used
The final proofing stage will also be a factor. For example, if a long cool final proof is to be used it should be followed by a short bulk fermentation period. We do this to prevent it over-fermenting the dough.
Dough continues to ferment in the final proof as well as the bulk fermentation.
Some types of bread require the dough to be gassy before a quick final proof, others prefer a quick bulk fermentation to receive bigger gains from oven spring.
How the length of fermentation changes the properties in the bread
As dough matures, as does oxygenation and the doughs ability to be extensible will decrease. Extensibility is the power of the dough to stretch without tearing.
As you can see from the diagram above it's a hard balance to decide how long to knead or bulk ferment a dough. There is never a “perfect” time as when we ferment for longer, extensibility and oxygenation increase. We also may have other constraints like preventing oven bottlenecking.
We have to “take a view” on when is the best position for the dough and be confident it’s “about right”.
Does long fermentation make the best bread?
Longer bulk fermentation (or first proof) creates more acids in the dough which will condition it and create more flavour. This is usually desirable but it is important to point out here that bread with shorter fermentation times can still be enjoyable.
Bread can be made in a short fermentation time. This is usually done with added fat to soften the crumb and add flavour. The bulk fermentation time will be reduced while the final proof time will be about the same.
Croissants are made relatively quickly to stop the dough becoming gassy. Overly gassy croissant dough can be a nightmare to laminate the butter and create layers!
It’s common to add a few additives like malt flour and ascorbic acid to these doughs to compensate for the lack of dough maturity.
Soft rolls and breads which benefit from a lighter taste and larger oven spring also follow a quick (or sometimes zero) bulk fermentation stage.
How long does a dough need to ferment?
For a standard straight dough after mixing we would expect a bulk fermentation period of around 2 hours, and final proof of 1½ to 2 hours.
If we want a weaker crumb and less flavour which is necessary for a few British loaves then we would reduce the rest time, but the final proof would be about the same. These create the characteristics of short fermented bread.
For speciality artisan bread, long fermentation is often achieved by using a fridge to slow down the rate of carbon dioxide production (alcoholic fermentation).
Why prove bread twice?
We prove bread twice to mature the dough in the first stage and allow the dough to rise to the shape we desire in the second.
Bulk Fermentation = Creates flavour and conditioning properties.
Final Proof = Is for the bread to be ready for the oven
How does no-knead bread fermentation work?
No knead recipes call for a light mix to evenly distribute the ingredients. Following this the dough passes straight to the bulk fermentation stage, pausing every hour or so for a stretch and fold.
Not kneading dough reduces the oxygen intake of the dough. This creates a structure which is weak. Bakers will counteract this by giving the dough a long bulk fermentation in the fridge.
Bread made with the no knead method has a “bouncy” crumb texture. For some bread types, it is arguably superior to kneaded dough -depending on who you speak to.
A no-knead method is perfect for some bread styles. It is also helpful when first learning how to make bread. But knead, knead a lot, knead a little or no knead, the same process of fermentation occurs, it just works slightly differently.
Further reading: How to do a stretch and fold
After an optimum bulk fermentation period, the dough is then divided (if making more than one bread), pre-shaped, left to rest for 10-20 minutes, shaped and then final proofed. The dough should be preshaped when the dough is at its maturity.
Final proof should last for 1½ to 4 hours, longer sometimes for sourdough.
It is possible to final proof the dough in the fridge which slows down the rate of alcoholic fermentation and can help manage your time.
The main reason for a fridge final proof is so you can have fresh bread in the morning when you don’t want to get up early.
Final proofing in the fridge
I advise against final proofing large bread in the fridge. The core of the bread will take longer to climatise in the oven which can make to a dense crumb with holes in it.
Removing the dough out the fridge for a few hours to warm up doesn’t really work as the outside ferments whilst the core remains dormant
Small diameter breads such as baguettes have no issue with proofing in the fridge as their core heats quickly. Some home bakers do final proof in the fridge as they find it easier to fit around their lifestyle this way.
I don’t recommend fridge final proofing for large diameter breads.
Fermentation during the final proof should principally be for raising the bread so it is ready for the oven, not flavour development. The final proof stage should be about filling the well made gluten structure with air.
I believe this should be done in a reasonably quick time therefore for best results I don’t think it is a good idea to final proof in the fridge.
Once the dough has risen to the required level and the baker is confident that gas production is slowing it is now ready to bake. Here the dough is often cut before being placed in the oven, usually with the addition of steam.
The cuts are primarily to allow excess gas to escape whilst baking, secondarily they are for aesthetics. The dough will continue fermentation in the oven which is visible from the oven spring.
Yeast is most active at around 35C (95F), though it won’t die until it reaches around 60C (140F). It takes about 10-15 minutes for the core of the bread to reach this point which means that heat intensifies fermentation, creating an explosion of gas.
If the right conditions in the oven are available the gas forces the dough to rise. This is what bakers call oven spring.
Further reading: How oven spring works
Enhancing dough fermentation
Autolyse is the process of adding the dough ingredients to a mixer, combining gently so the flour is hydrated and left to naturally ferment. The dough is left to relax for 20 - 40 minutes before the mixing commences.
Autolyse allows time for the flour to hydrate and speed up its natural fermentation and for some the organic acids to populate which will help the dough mature.
By autolysing we oxygenate the dough naturally. When using this method we should reduce the mixing time by around 15%.
The key benefit of using an autolyse is the reduction of flour oxygenation. This is achieved by maturing the dough before mixing is undergone.
Further reading: The autolyse process for bread makers
Using prefermented flour to make bread
Bakers often ferment a quantity of the flour, water and yeast (usually a tiny amount) around 12-18 hours before adding it to the actual dough mix. We call these preferments.
- Pate fermentee
- Wet sponge
- Sourdough starter
(Sourdough is covered in detail below)
Using a portion of flour which has already undergone fermentation adds many of the positive benefits of long fermentation.
A combination of the flavour and structure enhancing benefits of the bacteria created in prefermented dough combine with lightly fermented flour to make bread that is complex, yet fast to make.
Prefermented doughs absorb natural yeasts in the air and flour encouraging more alcoholic fermentation than the yeast provides. The maturity from prefermented flour drives flavour and strength into the dough, reducing mixing and bulk fermentation time.
Biga and poolish are made by combining a proportion of the flour and water with a small amount of yeast. The mixture is left for 12-18 hours and then added to the dough.
Further reading: How levains make bread rise
A Pâte Fermentée is a piece of yesterday's dough incorporated in the mix, passing down its flavour and raising properties into the dough.
Retaining a piece of dough every day for use in the following creates a powerful levain.
A soaker is a mix of flour and water. This benefit of a soaker is solely flour development. It’s not going to involve yeast fermentation, but will develop the starch and make a stronger gluten structure.
Soakers are often used in wholemeal doughs to unlock the complex starches that are contained in the flour.
Using the soaker method will lighten the texture and make a strong gluten matrix, just be careful of over oxygenation so a short bulk time is best suited.
Is long fermentation is better than short?
Fermentation quality is not just based on time. Temperature, humidity, flour quality, ratios of the ingredients all make a difference to the rate of fermentation activity.
The best way for a baker to have the best fermentation is to use good quality ingredients, including bakers flour and to manage the temperature of which the fermentation occurs.
Once the best conditions are created, time is the biggest factor.
Long fermentation creates more taste and aroma, combined with better raising properties. Bread made slowly is often deep, interesting and extremely welcome.
Fermentation of sourdough bread
Sourdough bread is made from a sourdough starter levain. A starter is created by adding water and flour together to make a sponge which is left to ferment. The following day more flour and water is fed to the starter.
Sourdough starters draw in natural yeasts from the air and in the flour which over successive feedings develops forms of lactic acid.
After 7-14 days of daily feedings, the starter becomes powerful enough to levain a loaf of bread. The starter sponge encompasses lactic acid and alcoholic aromas and flavours which are passed onto the bread.
The lactic acid contributes to the twang we associate with many sourdough breads.
L. sanfranciscensis is the strand of yeast that multiplies in sourdough. Unlike the strand found in traditional yeast, it breaks down maltose directly. In fact it uses maltose to thrive.
This is great for hydrated flour as plenty is created at a slow, continuous rate as it develops.
When baking with a sourdough starter we can increase the twang by fermenting at the ideal temperature of 34C (93F). If you don’t like the twang lower the temperature.
Lowering the temperature by bulk fermenting in the fridge allows acetic acid to populate more vigorously than lactic acid. Creating a more vinegary, less twangy tasting bread.
Bread baked with a sourdough levain has a slow oven spring. It is common that sourdough bread will have a denser crumb than most yeast leavened bread because of this.
The conditions of sourdough affect the flavour and aroma of it. The type of flour, the air, water, humidity and temperature all make a difference. San Fransisco makes some of the most popular sourdough bread in the world. Many bakers have imported dried sourdough from places like San Francisco to use in their bakeries.
But they quickly discover the environment reverts the starter to be just like the one they already had after a couple of days.
Sourdough bread has good keeping qualities, have a supple and elastic crumb and an amazing deep aroma. The taste and look of baked sourdough bread, sometimes called a Pain au Levain should be well rounded, deep and beautiful.
Some bakers use a hybrid levain of sourdough starter and a small amount of yeast. This aids the oven spring and makes the bread lighter whilst retaining the benefits of using sourdough.
This is especially true in cold weather when fermentation takes longer.
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Changing the qualities of dough fermentation
We’ve covered the stages of fermentation and the use of sourdough, preferments and traditional yeast to create different types of dough fermentation.
There has been mention of how changing the fermentation makes modifications to the bread, now let’s look at a few variables that we’ve touched on in a little more detail.
How to slow down the effects of fermentation
We’ve covered how slow fermentation can be useful, it is also sometimes necessary to slow down the rate of fermentation like when the room or dough temperature is too warm or it has been overmixed.
Here are a few techniques I’ve used in the past to reduce the effects of fermentation:
- Use less yeast or levain.
- Reduce the temperature
- Increase the amount of sugar in the recipe to levels of over 5%
- Salt slows down yeast activity, use more.
- Add less water. Drier, stiffer doughs develop slower as it’s harder for the natural enzymes to move about.
- Decrease the humidity - ok, I have not done this but if you have equipment that can, then do - but only if you need to.
(To increase the rate of fermentation, do the opposite)
How important is the temperature of bulk fermentation?
Controlling the temperature will maintain the expected rate of fermentation. Yeast likes to work at 38C (100F) but this is not always ideal for artisan bread. Many bakers like to slow down the rate of yeast fermentation by cooling the temperature of the room and the dough.
Yeast is most active in warmer temperatures. Depending on the brand, they tend to work best at around 38C (100F). Above this optimum temperature, the yeast cells start to die off which slows the process of the fermentation.
If the temperature drops below 38C (100F), gas and ethanol production slows down. As the yeast fermentation reduces, the flour still continues to break down into longer and stronger gluten strands. It also develops more and more starches.
Importantly, a brand of more complex starches is extracted from the flour.
The role of complex starches in bread making
A long, cool fermentation unveils more complex starches in the dough. They take longer to break down which is why this kind of long fermentation is necessary to uncover them. If warm fermentation temperature is used, the yeast would proof the bread regardless. These complex starches would remain hidden in their previous carbohydrate forms.
These additional starches are food for the yeast in the form of glucose.
Though, they aren’t always used up.
What doesn’t get used up in fermentation remains in the bread. They will create additional sweet flavours and generate those dark colours we associate with artisan bread crusts.
The perfect fermentation temperature
Even though yeast prefers warmer temperatures, it might not be the best way to proof bread if we want the most flavour. More complex starches that are broken down will create a sweeter flavour and we want to benefit from the creation of the acids to mature the dough as well.
Artisan bakers use cooler environments to ferment bread, typically around 24-28C (75-82F).
Cool fermentation is achieved by cooling the water added to the dough and using lower settings on automatic proofers.
Using the fridge to ferment bread
Dough can be kept in the fridge to bulk ferment. This technique is often used for overnight bulk fermentation. It helps all the previous advantages mentioned of long fermentation, but makes an even more intense flavoured, aromamatic and sweeter tasting bread.
Cold temperature allows broken starch and maltose to be broken down from the flour, unlocking different flavours.
This generates a sweeter, but mature taste that is only available in cold fermentation. The broken starch particles that occur in all flour types get repaired which helps the structure of the crumb and extends the life of the bread.
This reinforces the rule I’ve used for years:
“The longer it takes to make a loaf, the longer it will be fresh”
Oh dear, I’ve realised by having a lot of "sayings", I’m turning into an old man!!….
A short mixing time is best before long fermentation to reduce oxygenation of the flour.
Pizza makers follow a slow mix, long fermentation time method to reduce wastage and to create an amazing, naturally sweet dough.
Using dough improvers in home baking
Though not strictly artisan baking, many bakers add a few extra ingredients that aid the fermentation process. Common ones are vinegar, bean flour, malt flour and ascorbic acid.
These do variable things like improving keeping quality of reducing the bulk fermentation time. You can find out more about common bread improvers in this article:
Further reading: Using dough improvers to assist dough fermentation.
Is fermentation important to bake bread?
It’s a fantastic process and yes, it is absolutely necessary to make bread. The ability to correctly ferment the dough without under or over-fermenting is a challenge that many bakers struggle with when learning how to make bread.
It's hard to get perfect, but near perfect is still good.
Follow a good recipe from a reliable source and take regular temperature checks for consistency.
As the dough gets warmer, fermentation increases so fermentation time should be reduced or the temperature should be cooled to compensate.