How A Levain Works To Make Bread Rise

A levain is the name of an ingredient used to activate dough fermentation. Yeast is the most common levain, with sourdough a close second, but there are others that are worth using as well.

What is the definition of a levain

A levain (or leaven) is the active ingredient which causes fermentation in a dough or batter. When the levain is yeast it reacts with simple sugars to create carbon dioxide gas and water through aerobic respiration. It’s carbon dioxide that gets trapped as a gas in the gluten structure and makes the bread rise. When undergoing anaerobic respiration, yeast cells undergo alcoholic fermentation to produce ethanol. Additional fermentation routes occur when the presence of lactic acid bacteria produces lactic and acetic acids. Lactic acid bacteria appear in sourdough and mature flour found in preferments and in long-fermented dough.

How a levain makes bread rise

Adding a levain to hydrated flour initiates yeast respiration. The yeast and moist flour develop enzymes which break down the starch in the flour to produce sugars in order for the yeast to respire. Yeast respiration creates carbon dioxide and ethanol. Lactic acid bacteria produce lactic acid and acetic acids amongst other proteins which are necessary to make the structure of the bread.

Maturing the dough

Bread is usually proofed twice. During the first rise (bulk fermentation), maturation develops flavour and forms a better environment for gas production. In the second (or final) rise the gas expands in the gluten structure to raise the bread.

The common route to accelerating the rate of dough maturity is to knead well and give it a long first rise. However, the type and the amount of levain used have a massive effect on the level of dough maturity.

What does the levain change in the bread?

The following characteristics change, depending on the levain selected:

• Gas production
• Gas retaining properties
• Keeping quality
• Flavour
• Ph value
• Rate of fermentation
• Oven spring
• The density of the crumb
• Crust colour
• Nutritional value
• Extensibility
• Aroma

Let’s now look at all the levains types we can use:

What is fresh yeast?

There are many strands of yeast available, with some still undiscovered. The one produced synthetically for bread production is Saccharomyces Cerevisiae. It’s a fungus derived from the waste of sugar beet production. To produce yeast, a fungus is grown and portions are removed for sale. The original mass continues to feed and multiply.

Fresh yeast is also known as compressed yeast. It’s kept in the fridge at all times which prevents it from drying up. Kept cold, it will last for about a month.  It is added to the dry ingredients as it is already active. It’s the cheapest type of yeast and contains around 60% water.

What is active dried yeast?

This is fresh yeast that’s concentrated using dehydration methods.  There is less water in Active dried yeast so the amount of yeast used is typically halved. For a more accurate conversion, multiply by 0.4. Active dried yeast needs to be activated in warm water for 6-10 minutes before use. The desired temperature of the water for activation is 41-46C (105-115F). Below this and an amino acid called glutathione leaks from the cell walls. This makes the dough sticky and hard to handle.

Many instructions for activating Active dried yeast include a small amount of sugar in the activation. Many bakers argue that sugar is too complex for enzymes to break down in this time. This makes the inclusion of sugar unnecessary. I have never added sugar, but a test awaits to see what generates the best result. Active dried yeast is slower to activate than fresh yeast which allows extra time for the gluten to develop before gas production begins.

Active dried and instant yeasts use an emulsifier to stop the product from drying out and clumping in storage. A common one is Sorbitan Monostearate. Without this, the yeast would be hard to measure. It doesn’t affect the handling or flavour of the dough, however, many bakers prefer to use minimal ingredients and prefer fresh yeast.

What is fast action yeast?

Fast action yeast is also known as instant yeast. It’s a dried yeast that is manufactured with a different method than Active dried yeast. The manufacturing technique and the addition of ascorbic acid make this yeast fast to ferment. There is also no requirement to activate it in warm water. Fast action yeast comes in smaller particles than active dried yeast. The ascorbic acid adds oxygen to the dough which strengthens the gluten structure. Instant yeast is more active than the other yeasts. To transfer a recipe from fresh to dried yeast, divide by 3.

What is osmotolerant yeast?

This type of instant dried yeast is suitable for doughs that contain over 5% sugar. Ordinarily, high amounts of sugar trap water in the dough. This makes the water unavailable to the yeast. Osmotolerant yeast works against osmotic pressure to allow the yeast to feed. The main (and only) brand I have discovered is SAF yeast gold. When using this yeast, the amount of water in the recipe is increased. You can use this yeast for ordinary dough, however, it is expensive and will last a long time if sealed in the fridge.

What are preferments in bread baking?

Before we cover what a preferment is, let’s go over yeast multiplication, and what happens during dough fermentation:

Yeast multiplication

When fermenting, yeast operates by multiplication. It starts off slowly and as the number of yeast cells increases and the dough proofs faster, and faster. It’s therefore technically possible to prove a large loaf with a tiny amount of yeast. It’ll just take a long while!! Though the dough will over-oxidate and lose extensibility before it does.

Dough fermentation

There is a lengthy tutorial on the dough fermentation process page, so I’ll keep this explanation as short as I can. Enzymes in the dough break down starches in the flour into simple sugars. These sugars are either fed to the yeast for alcoholic fermentation (the production of carbon dioxide and ethanol) or feed on other enzymes to become organic acids. 

The acids and ethanol improve the dough in a process we call dough maturation. The benefits of these are explained below. For the dough to mature it needs, time to ferment. This occurs in the bulk fermentation stage. Modern bakeries often use enzymes and dough conditioners to reduce this step. To enhance the dough maturity a long bulk fermentation time can be followed or a preferment can be used.

The benefits of mature dough:

Dough that is well matured will aid the bread by:

• Gently softening the hydrated flour to form strong and long-extensible gluten
• Drawing flavour from the complex starches and breaking down amino acids in the grain
• The generation of organic acids which add flavour and aroma
• Increasing the natural sugars makes the crust darker
• Lowering the ph value of the bread adds flavour and improves keeping quality.
• Improving keeping quality
• Better gas retaining properties
• Producing gas

How preferments work

As a general rule, a dough that undergoes a long bulk fermentation will be a superior bread. To save time waiting for the dough to develop we can introduce dough that has already undergone some fermentation. This prefermented dough can be a biga, poolish, pâte fermentée. Actually, a sourdough starter can also be classed in the preferment category as well. 

Wouldn’t it be better to have a longer bulk fermentation?

The main reason a preferement is chosen over a long bulk fermentation is that it saves time. Maturing the flour is important to make good bread. But why choose preferments over a long bulk fermentation?

• Saves time
• Bakeries can prepare orders
• Does not require a fridge
• Saves space when working with large quantities
• Less acid flavour than sourdough
• Lowers kneading and bulk fermentation time
• Less oxygenation of the flour
• The combination of prefermented flour and fresh flour creates unique depths of flavour

Let’s cover the prefermented flour options commonly used in bread baking:

How to make a poolish

Common in French baguettes and many other French breads. This wet sponge was taught to French bakers by Polish settlers and later adopted. It uses a small amount of yeast combined with equal quantities of flour and water. It’s gently mixed until only just combined, covered and left to ferment for 12-18 hours. The end result is a vibrant, structured levain. Authentic poolish has a maximum of 0.25% fresh yeast to 100% flour and water. For example:

200 grams water
200 grams flour
(200* 0.25%) 0.5 grams yeast

It’s a wet mixture which makes the tiny amount of yeast work fast. More yeast is often added when the remaining ingredients are added. Here’s a baguette recipe with poolish to give you an idea of how it works.

How to make a biga

The Italian biga is a stronger, thicker pre-ferment. The same method is followed, but uses less water, making a dough-like mixture. Yeast levels can go up to 0.5% as the activity of fermentation is slowed with a less hydrated dough. Additional yeast is not supposed to be added at the mixing stage. A biga is stronger and more powerful than a poolish, though, slightly less flavour is produced. Biga is perfect for generating flavour in lighter flavoured flour that is grown in Italy.

What is a pâte fermentée?

Despite the use of French lingo, it’s not sexy. A pâte fermentée is a bit of old dough…But it’s still exciting for many bread bakers! The theory is that if you made a batch of baguettes every day and after every bake, you kept a bit of the raw dough. The next day, this piece of old dough goes into the next batch of baguettes.

Repeat this every day and the old dough will develop like sourdough. It generates its own ecosystem of organic yeasts and bacteria. These will ooze a depth of flavour and vibrancy that can’t be matched. Whilst also being capable of raising the dough.

This technique was common in France and is still used in select Parisian bakeries today. Imagine the taste and smell of a bread that used pâte fermentée each day for years? Amazing! The poolish can simply be added to the bowl at the start of mixing or some bakers prefer to add it in chunks midway through kneading. It can also be re-hydrated into a poolish and left for 12-18 hours.

What is a sourdough levain?

A mix of flour and water is left for wild yeasts found in the air to gravitate and ferment. The wild yeasts are also accompanied by organic acids. The lactic acid bacteria develop making sourdough-made doughs mature. High levels of lactic acid found in sourdough also contribute to gas production.

It takes at least 7-14 days of regular feedings to create a sourdough starter from scratch. A sourdough starter is a both prefermented flour and natural levain. It preys on feeds of flour to stay alive. Once built, you can keep a sourdough starter forever.

To make a sourdough starter, mix equal quantities of flour and water, cover and leave for 24 hours. The following day 3 quarters is removed and discarded whilst the remainder is fed with flour and water and again left overnight. The process is repeated for several days until the sponge is ready to proof bread.

How to make a fruit levain

One of the earliest levains is primarily used in the production of alcohol. Fruits draw natural yeasts found in the air to their surface. When mashed together with the sugars found in the fruit they start to ferment. In the case of wine, sugar is created by grapes and yeast is found on the skin of the grape. In other drinks, extra yeast and/or sugar can be added to make bubbles, extra alcohol and flavour.

How to make homemade yeast

Making homemade yeast become popular since lockdown restrictions caused yeast prices to skyrocket. The idea is simple, take an item that contains natural yeasts such as a grape. Soak in water for a few days and add flour (the carbohydrate) and stir. The flour will feed the yeasts and you will have a homemade levain!

Bicarbonate of Soda

A reaction happens as two opposing Ph factors combine. When bicarbonate of soda is added to the other ingredients it reacts with the opposing Ph value forcing a chemical reaction. Gas is released and the bread, cake or whatever it is goes up! Buttermilk can be used instead of water as it is more alkaline. This creates a larger reaction as it combines with the acidic ingredients, to make a bigger rise.

The dough only goes up once, so the dough conditioning we enjoy with yeast or sourdough based levains does not occur. Bicarb bread is lighter in flavour, but takes less time to make.

Wet sponge soaker

A soaker is a mix of flour and water that is left for 2+ hours. It’s not a levain as it doesn’t contain any yeast, but it is a type of preferment. I have been using a soaker recently and getting some great results. A soaker will develop the flour, similar to an autolyse. It’s not going to involve yeast fermentation as none is added.

A sponge soaker breaks down the starch and allows the gluten strands to unwind. The more complex starch particles are broken down which creates sweeter notes in the flavour of the bread. The process is similar to autolyse but not all of the flour from the recipe is used and development times are longer.

They’re used in wholemeal doughs to unlock the complex starches contained in the flour. I also make a seed “soaker” to hydrate the seeds overnight before adding them to the dough the following day. To prevent over-oxidation use a short bulk time with this preferment.

Can you add too much levain to your bread dough recipe?

Adding a high amount of levain to a recipe changes the flavour, aroma and structure of the bread. Typically, what will happen:

• It will taste of it, possibly nice if it’s sourdough, but horrible if it’s a yeast straight dough
• The rise is quick which reduces flavour development and gluten formation
• Erratically rising in the oven
• Responsible for holes in the bread crumb
• Rips in the crust

Here’s an article which gives more insight into using too much yeast in bread.

How much levain should I add to my bread recipe?

There’s no golden rule, but there are a few starting points when crafting a new recipe. Here are the common levain percentages based on the total amount of flour used in the recipe:

• Fresh yeast 1.5-2.2%
• Sourdough 10-50%
• Poolish 20-50%
• Biga 25-60%

The maximum amount of fresh yeast that should be used is 2.5%. Above 2.2% can bring the taste of yeast to be noticeable. I don’t generally go above 30% of sourdough. In cool climates, without using a proofer it may be an idea to increase this up to 50%

Which levain is right for me?

It depends on the bread that you want to make. The levain of choice will impart a flavour and structure characteristic that’s different to another. It’s best to start baking with one levain, mastering it and then trying something else. Yeast leavened bread is the easiest way to get started. It’s easier to learn the basic skills of baking without adding new variables.

Ending thoughts on what is a levain

I hope you have grasped the differences between the levains in this article. Understanding their differences will help you to use them and perhaps, experiment with your favourite recipes in the future. If you’ve not already, check out my beginner’s bread recipe to get started right away. Let me know if you have any questions in the comments below.

Frequently asked questions about levains