Fermentation is truly the core of making bread. It's the science behind how flour, water, salt and yeast come together to transform into bread. This article reveals how important dough fermentation is and deep dives into the science of bread making.
The majority of bakers won’t know this information. And, to be honest neither did I until a couple of years ago! But after I took some time to understand what is really going on I have found the quality of my bread skyrocketed!
Learning the science allows bakers to cut through the bad advice found online and make better choices.
After reading this detailed guide you’ll know how dough fermentation works and understand how to consistently make quality bread. We’ll also cover how flour breaks down to develop structure and support the yeast.
What is fermentation?
It is used to produce many popular food products like cheese, yoghurt, alcohol, pickled foods and bread. For fermentation to occur, it requires a base, and a strain.
The base is a carbohydrate, and the strain is a type of bacteria.
In bread making, the base will come from the carbohydrates in the flour, and yeast is the strain.
What is the dough fermentation process?
As soon as yeast comes into contact with flour and water, the fermentation process starts. Alcoholic fermentation produces carbon dioxide gas which gets retained in the gluten structure. As more gas is produced, the gluten stretches and the bread rises.
Other components of fermentation include ethanol, lactic acid, acetic acid and various organic acids.
Once the bread has risen it goes into the oven where a further rise called oven spring occurs. As it gets too hot, the yeast bacteria dies, which brings the fermentation process to an end.
Is yeast fermentation the same as dough fermentation?
Yes, same thing. The yeast is the strain that creates the activity for dough fermentation, so both terms are interchangeable.
How yeast respires
It’s often explained that yeast feeds on sugar found in the flour. It is easier to explain with the term “eat” or “feasts”. But; simple single cell sugars penetrate the cell walls of the yeast allowing the yeast to respire and multiply. This is the process of anaerobic respiration. The outputs of anaerobic respiration are carbon dioxide (gas) and ethanol.
What is aerobic respiration?
Anaerobic respiration is the enzymic action of the microorganisms (yeast).
An enzymic action is:
“Any chemical reaction or series of reactions catalysed by an enzyme.”
Source: Biology Online
Alcoholic fermentation is anaerobic so oxygen is not needed. Other types of fermentation make things perish and mouldy. Anaerobic respiration isn’t the only form of fermentation in bread. The other type matures the dough.
How aerobic respiration makes bread rise
Alcoholic fermentation creates carbon dioxide. The gas gets trapped in small pockets in the gluten matrix. As the yeast continues to respire, more gas is produced. It fills the pockets throughout the bread and forces them to expand.
These bubbles of trapped gas form the crumb and are easily visible once the bread is baked.
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 lighter texture.
How carbohydrates are used in the process
Carbohydrates make up around 60-70% of the flour used in bread making. They supply sugars to the yeast for fermentation and generate flavour.
What are carbohydrates?
There are three forms of carbohydrates; simple sugars, starch and dietary fibres. Here’s what they do:
These sugars need little to no breaking down to be absorbed through cell walls. This makes them not great for our bodies if consumed in high doses. They are quickly absorbed into the bloodstream to provide a quick burst of energy.
Glucose, fructose, maltose, sucrose (table sugar) are simple sugars.
These complex carbohydrates contain strings of simple sugars connected by glycosidic bonds. Starches can be broken down by enzymes to simple sugars. Without being broken down, starch doesn’t have a sweet flavour as its complex make up prevents this.
Starch is produced by vegetables to store energy. Many other uses of starch are explained in this video:
Dietary fibres are more complex strings of sugars. These carbohydrates are too complex to break down easily. It takes loads of time and plenty of bacteria to unlink these chains into simple sugars. Eating food that is high in fibre is recommended by experts to aid our digestion systems as we use it to remove waste from our bodies.
White flour has a lot of the grain removed which makes wholemeal bread a better source of dietary fibres.
Monosaccharides and disaccharides
There are two categories that simple sugars fall into:
Monosaccharides are single sugars which include glucose, fructose and galactose.
Lactose, maltose and sucrose (table sugar) are disaccharides. These are two monosaccharides bonded together.
In natural ingredients such as honey or jams it is common to find a combination of monosaccharides and disaccharides. The sugars in flour are mainly glucose, levulose and sucrose and maltose.
The enzymatic action of yeast
Only the smallest sugars (monosaccharides) can penetrate the yeast cells for fermentation. This means the starches must be broken down into disaccharides and the disaccharides into monosaccharides to provide a supply of food for the yeast.
To break down the starch, the yeast produces enzymes.
Invertase is produced to break down sucrose a disaccharides into two monosaccharides, glucose and levulose. Maltose is two bonded glucose sugars so when broken down by the maltase enzyme, we are left with glucose.
The monosaccharides obtained can enter the yeast cells for anaerobic fermentation. They provide the yeast with energy to continue respiration. It does this using the enzyme, zymase.
Zymase is an enzyme that kick starts fermentation. It occurs from yeast and turns the monosaccharides, glucose and levulose, into carbon dioxide and ethanol.
Is ethanol needed in the dough?
Ethanol produced during fermentation is not a by-product of the formation of carbon dioxide. It is absolutely necessary to mature the dough.
During baking, much of the ethanol evaporates, but traces will remain. In bread, ethanol improves odour, flavour and keeping quality.
Aside from alcoholic fermentation, yeast produces various acids. These largely comprise of lactic and acetic acids. Others are categorised as “various organic acids”.
These collections of acids change the physical properties of the dough by aiding the ability to:
- Hold shape
- Stretch (extensibility)
- Retain gas
- Produce gas
- Keep fresh for long
- Deep flavours and aromas
- Lower Ph value
During dough fermentation, organic acids in the dough increase. Providing other variables are constant, the longer a dough undergoes fermentation, the more organic acids will exist.
Organic acids are essential to making bread, without them bread wouldn’t be nice to eat.
They help in the production of the bread as it’s 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.
Lactic acid is an important feature of sourdough starters and yeast breads. It has the highest concentration of the acids found in bread and is the key component in sourdough fermentation.
Lactic acid lowers the ph value of the dough and offers many benefits:
This acid is the key component of malt vinegar. It is also found in sourdough breads in lower concentrations. Here is how it benefits the dough:
Various organic acids
Organic acids also mature the dough and to build a bread with improved qualities.
I haven’t mentioned salt yet, but it does play an important part in bread making. Salt has three roles:
- It supports the structure of the gluten
- Slows down the activity of the yeast
- Enhances flavour
Though bread can be made without it, we should add salt for great looking and tasting bread.
How to change the rate of dough fermentation
Fermentation occurs primarily during the bulk fermentation stage, but it’s not soley based on the length of time allowed. Temperature, humidity, flour quality, ratios of the ingredients make a difference to the rate of activity.
Here’s a list of techniques you can use to slow it down. Some can be used to fix problems midway through a bake. For instance, if the temperature is too warm or a dough has been mixed a little harder than planned.
Here are a few techniques I’ve used in the past to reduce fermentation:
- Use less yeast or levain
- Reduce the temperature of the room (fridge)
- 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
- Reduce the final proof duration
To increase the rates of activity, these techniques are flipped.
Why slow down fermentation?
A slower fermentation provides several benefits to the dough, which we will discuss next.
The temperature of fermenting dough is a big variable. In a home kitchen, temperatures fluctuate which will impact the timing of the rise. It will also affect the flavour and texture of the bread.
Skilled bakers can use temperature to control the rate of production and create unique flavours.
The ideal temperature of the yeast
Yeast is most active when it’s warm. The optimum temperature for yeast fermentation is 36C (97F), above this it slows down. It slows down at cooler temperatures before reaching 0C (35F) where it is dormant.
That said, we can (and often should) consider bulk fermenting and proofing at cooler temperatures.
How proofing temperature affects the flavour
Maltase, the enzyme produced by the yeast to break down complex sugars into glucose operates most effectively at 25C (77F).
As complex sugars are not sweet in flavour. They have to be broken down by enzymes such as maltase and Invertase to reveal sweetness. To increase sweet flavours we can ferment bread below 25C (77F). This ensures there will be an abundance of monosaccharides, too many for the yeast to feed on. The remaining simple sugars are then used to sweeten the bread.
If the temperature of the dough rises above 25C (77F), maltase gets less effective and produces less monosaccharides. There will however be plenty of monosaccharides for yeast fermentation.
As the anaerobic respiration is accelerated, gas is produced at a faster rate than organic acids develop. The result is a bread that is not as sweet - but not necessarily inferior.
Getting too warm
If the dough rises above 36C (97F) you would see an initial burst of fermentation but the enzyamic process of breaking down the disaccharides into monosaccharides ends. Soon the yeast has nothing to feed and the respiratory process slows right down.
By adjusting the fermentation temperature, the availability of simple sugars changes along with yeast activity. So we change the speed of production and the sweetness of the bread.
Other benefits of cold fermentation
Cold fermentation assists broken protein particles to repair. This reinforces the strength of the gluten structure and extends the shelf life of the bread. It also means the lower protein flour can be used for bread, provided a long fermentation is used.
The perfect artisan fermentation temperature
Artisan bakers typically operate first rise at 24-26C (75-79F), but the second rise can vary. A 32C (90F) final proof is possible, whereas cooler is acceptable, including an overnight rise in the fridge.
Using the fridge for fermentation
Dough is often placed in the fridge for bulk fermentation or its final rise. It helps to manage timing whilst aiding the flavour and maturity of the dough.
As the temperature reaches zero, the respiration halts completely. Yet enzymic actions continue, creating a more intense flavoured, aromatic and sweeter tasting bread than usually possible.
“The longer it takes to make a loaf, the longer it keeps fresh”
Controlling dough temperature
One way of adjusting the dough temperature is to change the temperature of the ingredients before mixing. There’s a formula in the desired dough temperature article which explains how to take readings with a thermometer and how to adjust the water temperature to achieve the correct final dough temperature.
Another way is to control the environment of the bread proofing temperature. We can do this by using a proofer or fridge to warm or retard the dough. At home, we can also speed up or slow down the rate of yeast activity by placing the dough in warmer or colder areas.
How to best manage bulk fermentation
To achieve exceptional flavour, quality ingredients must be used alongside good temperature controls.
When the ideal conditions are created we only need to control one factor, time.
The final rise and baking
What happens when bread is ready for the oven
As time goes on, the process of enzymatic activity continues to provide zymase to the monosaccharides until they become exhausted, or the gluten structure becomes so filled with gas it becomes too heavy to support itself.
At this point the dough is proofed and ready for the oven.
Why does bread stop rising in the oven?
As the bread bakes the temperature rises too high initially for the maltase to break down enough monosaccharides for the yeast to feed.
If the dough rises above 36C (97F) you will see a quick rise known as oven spring.
For crusty bread, water is added to the oven to make steam how to add steam to an oven for bread.
The yeasts activity will continue in the oven which is visible as oven spring. This is where the yeast feeds on the remaining sugars rapidly in the warmth of the oven until it gets too warm or the crust sets. At this point the bread can no longer rise.
The oven spring lasts for around 10-15 minutes and is vital for light crumbed bread with a crunchy crust.
When the oven temperature reaches 68C (155F) the yeast bacteria dies bringing yeast fermentation to an end.
Yeast is a bacteria, a tiny living organism. All it is doing as is having a pretty good feast and multiplying. Like other bacteria once it gets too hot it becomes permanently inactive.
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 and check out my guide on bulk fermentation. It shows pictures on what the dough should look like at this stage.