How does a levain make bread rise?

A levain is the collective name of the ingredient used to activate dough fermentation. Yeast is the most common levain, sourdough is also popular but there are plenty more. Understanding the differences between the levains available to us we can open up new possibilities in bread making.

How a levain creates dough fermentation

At the start of mixing the levain is added to the dough and gets to work developing the starches in the hydrated flour to create enzymes, acids, ethanol and carbon dioxide gas. At the same time the hydrated flour develops protein from the flour into gluten. The gluten forms a structure of small bubbles which retain the gas produced by the levain.

How dough fermentation worksThe doughs structure develops during mixing and bulk fermentation and once shaped and in the final proof stage it rises before being ready for the oven. The ethanol that resides alters the acidity (ph factor) to develop flavour and colour in the crust.

Fermentation starts as the ingredients combine in the mixing bowl. It continues until the heat of the oven ends the activity of the levain.

For a more detailed explanation on dough fermentation, check out the what you need to know about dough fermentation article:

Further reading: How dough fermentation works

A definition of a levain

A levain (or leaven) is an active ingredient that causes fermentation in a dough or batter.

Fermentation in bread baking include gas production and dough maturity. The choice of levain and the conditions fermentation is conducted will alter the characteristics of the dough made. Leavins affect the following qualities in the dough:

  • Gas production
  • Gas retaining properties
  • Keeping qualities of the bread
  • Flavour
  • Ph value
  • Rate of fermentation
  • Oven spring
  • Density of the crumb
  • Crust colour
  • Nutritional value

To be honest there's probably more that I've forgotten here, feel free to send me a message if you can think of any more that I need to add!

So we know yeast and have probably encountered sourdough, but what is the reason for choosing them and what other levains are there?

Levains a baker can use

Take a look at the levains available to bread bakers, which one will you choose?


This was one of the earliest forms of levain, and used in the production of alcohol, some fruits draw natural yeasts found in the air which multiply into a levain. 

In the case of wine, sugar is created by grapes and yeast is found on the grapes skin. 

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The two ingredients needed for fermentation are obtained from the same fruit! In other drinks an extra amount of yeast and sugar are added for bubbles, extra alcohol and/or flavour.

There has been a increase in popularity of what was an underground motion of making home made yeast for bread making with water and fruit.

The idea is simple, take an item that contains natural yeasts, soak it in water for a few days to release them. Then add flour (the carbohydrate) and give it a stir. The flour will feed the yeasts and you have got a home made yeast ready for bread baking.

Fresh Yeast

how does a levain make bread rise

The full name of the chemical that we throw into our mixing bowls is Saccharomyces Cerevisiae.

It’s a fungus derived from the waste parts of sugar beet production.

To create it in volume, it’s grown from a big bit of yeast like a plant and like a plant is clipped, portions of yeast are removed and sold whilst the original mass is fed and regrows. 

Fresh yeast is often called compressed yeast in bread manufacturing circles. It should be refrigerated at all times, otherwise it dries up quickly. Kept cold, it lasts for about a month. There is no need for activation as it is already active. It contains around 60% water.

Active dried yeast

This is fresh yeast that has been dehydrated, making it more pure. The water content of active dried yeast lower than fresh. When adapting a recipe used from fresh yeast you should multiply the amount of fresh yeast by 0.4, or just half it if you are lazy.

Active dried yeast does need to be activated in warm water for 10 minutes before use. Sme recipes mention that sugar should be added to the water to speed up activation, many scientist argue that sugar is too complex to be broken down by the yeast in this time so it is pointless. A test awaits...

Either way active dried yeast is still a bit slower to get going when compared with fresh yeast. This can be prefered in terms of flavour development from the flour.

Yeast uses an emulsifier, often Sorbitan Monosterate to stop the product clumping and stop the yeast from drying out too quickly. Without this the yeast would be hard to break off and measure. This does mean that an extra ingredient is added to the recipe which may affect the handling of the dough, so I prefer to avoid when necessary.

Fast action yeast

Fast action yeast is also called instant yeast. This is a form of dried yeast that does not require activating. This can be very advantageous as it reacts quickly without a need for activation in warm water. Fast action yeast come in smaller particles than active dried yeast. It also has 33% more activity than active dried yeast.

Less yeast needs to be used when using this variety. To calculate a recipe from fresh to dried yeast, multiply by 0.33.

Fast action yeast is suitable for use in bread makers. All sounds good yeah? However, it contains further additions to gain these results. The usual one is ascorbic acid which is vitamin C. This completely changes the properties in the dough and improves the gluten structure.

Some home bakers may find there bread improves when they choose this yeast as it includes ascorbic acid. I prefer to add it myself on the doughs I whish to use it.

I prefer to steer clear from fast action yeast for hand baking. However, if I was using a bread maker to make bread, I would use it every time.

Osmotolerant yeast

This type of instant dried yeast is suitable for doughs that contain over 5% sugar. Ordinarily high amounts of sugar will trap the water in a dough making it unavailable for 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. If using this, extra water should be added. You can use this yeast for ordinary doughs however it is one of the most expensive yeasts available and will last a long time if sealed and refrigerated once open.

Yeast in multiplication

When doing it’s thing, yeast operates by multiplication. It starts off slowly and goes faster, then faster, with each minute more powerful than the last.

It’s why it’s possible to prove a large loaf with a tiny amount of yeast. After a while!!

The dough may over oxidise and lose it's gluten structure strength before it does but, it will rise...



  if the right conditions of temperature, time and humidity are made for it then the slow fermentation can lead to a superior dough.

Pizza doughs are typical of this style. A big batch of dough is fermented for 24 hours with a tiny pinch of yeast, as low as 0.1% of the flour weight is all that is used sometimes!

Low amounts of yeast used in a bread dough can allow the flavour of the flour to come through in the final product. 

I suppose it just matters how low and how long you want the dough to ferment.


The preferment type of levain encompases all levains that utilse flour that has been pre-fermented. The prefermented period can last a matter of hours, overnight or in the form of some sourdough starters, from years of nurturing. Preferments contain either natural or commercial yeast or often both.

The mixture develops through the hydration of the flour and alcoholic fermentation. The preferment expands in the bowl to form a structured levain the following day. It is then added to the bread mix along with further flour, water, yeast (not always), salt and any further ingredients.

Biga used to make bread rise

Using a preferment gives the dough many benefits including:

  • The flour gets softened and broken down gently by the water, allowing the best possible platform for gluten development. 
  • More flavour is drawn from the flour as it gains a sweet taste from complex starches being drawn out of the grain.
  • The yeast fermentation create acids which add flavour too the dough
  • The crust of the loaf becomes darker due to an increase in natural sugars.
  • The bread will taste less of yeast as less is used.
  • Mature dough has better gas retaining properties

Using preferments are great for doughs that need to retain large air bubbles like Ciabatta and Focaccia, the dough structure is strong and holds a lot of air.

Mixing and bulk fermentation time of the dough will be reduced which reduces the risk of over oxygenation.

For a longer fermentation we can use less yeast, water, or cool it.

When is a preferment ripe?

Using a preferment when it’s ripe takes a bit of getting used to. When ripe, it should have bubbles that are breaking up the surface and it should have risen about 50%. Under ripe and the subsequent dough will be weaker and less able to retain gas.

If it’s over ripe, the preferment collapses under its own weight. If it’s used, the preferment won’t support the crumb structure of the bread and gives it a sour taste.


This wet sponge was taught to French bakers by Polish settlers.This type of levain takes a small amount of yeast adds it to equal quantities of flour and water, mixed to combine, covered and leave to ferment, typically overnight. The end result is a vibrant and structured levain. 

Authentic poolish has a maximum of 0.25% fresh yeast and the flour and water amounts be equal. It's a wet mixture so fermentation is fast -making the little bit of yeast go far. Yeast is often added during the mixing of the dough.


Whereas the Italian biga, makes stronger, thicker pre-ferments. Less water is used to make a more dough like strength preferment. Yeast can go up to 0.5%. It needs to be increased as the activity of fermentation is slowed down where the dough is less hydrated.

Further yeast is not added at the mixing stage. A biga is stronger and more powerful than a poolish, though slightly less flavour is produced. This is perfect for generating extra flavour from the lighter tasting flour that are popular in Italy.

Pâte fermentée

Basically, a bit of old dough. Despite the use of a bit of French lingo, it’s not that sexy. It’s a bit of old dough…

...But I’ll try to excite you. If everyday you make a batch of baguettes and keep a bit of the dough behind. The next day you add the piece in the following days mix.

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This adds a bit of flavour, structure and raising properties into the next days bread. Repeat this everyday and after a while the old dough will ooze with a depth of flavour and vibrancy and will be capable of raising the dough on its own. 

Imagine the taste and smell of a bread that used pâte fermentée each day for years? 


If you want to learn how to use this artisan bread making technique, you can either cheekily throw it in the bowl during mixing. Or, re-hydrate in a poolish, leave for 12-18 hours and use it the following day.

A bit of fresh yeast is often added to maximise the raise, but is not necessary when a mature pâte is used.


A mix of flour and water left to ferment by yeasts that naturally occur in the air. An active sourdough starter is refreshed every day with flour and water. The preferment absorbs yeasts and bacteria from the air in which it grows. This causes it to take on flavours and properties unique to its environment.

This makes every sourdough unique.

A sourdough starter is a both prefermented flour and a levain. It preys on feeds of flour to stay alive. To make a basic sourdough starter you mix equal quantities of flour and water and mix until there’s to lumps. Cover it and leave for 24 hours.

The next day you take half out to throw away and add equal quantities of flour and water again. This process repeats every day until around 7 days when your fresh, ripe levain will be ready to use.

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The idea is that after using it, you always keep a bit of it and refresh and keep the sourdough alive for the life of the bakery.

We usually use white flour for sourdough baking, but adding a proportion of other flour such as rye, spelt or doing a 100% ancient grain sourdough creates breads with alternative flavours. 

When first starting a sourdough, it’s possible to add some ancient grain wheat, fruit, honey or yogurt to help get the sourdough started. This works to combine a fruit levain with naturally occurring ones to give it an initial boast.

But simple flour and water is fantastic anyway.

A sourdough starter is resilient to atmosphere changes and can even be revived after weeks of starvation. It’s tough!

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How does Sourdough work?

Sourdough works like the previous yeast examples by reacting with starch to create gas and ethanol. The strain of yeast that is most prominent in sourdough is Lactobacillus Sanfranciscensis which is a form of lactic acid bacteria. The strand in common yeast is Saccharomyces Cerevisiae.

Actually it’s the lactic acid which flavours sourdough bread with that creamy twang we associate with it. 

In comparison sourdough leavened breads are slower to rise and have a slower oven spring than yeasted breads. Sourdough has more influence from the lactic and acetic acids which harbors better keeping quality, more flavour, aroma, gas retention, mixing and bulk fermentation times and better dough handling properties than yeast breads. 

Is sourdough the best levain?

To many people a sourdough starter is the ultimate levain, and in paper it can look like that. It has all the benefits of on all in one solution, dough maturation, raises the bread, nice flavour... 

how does a levain make bread rise

A yeast leavened dough can use a preferment to get many of the characteristics that a sourdough levain brings. If it doesn't then a longer bulk fermentation is recommended to develop the dough. That said if we want a lighter tasting dough then less dough fermentation is best. This is where sourdough is not recommended.

Sourdough does bring a lot of flavour to a bread, sometmes overpowering. I belive it is great, but yeast based levains such as biga or poolish can create supperior breads.

I belive there is a place in artisan baking for both.

Bicarbonate of Soda

I’m no bicarb expert sadly. But I can share with you how it works:

A reaction happens as two opposing Ph factors combine. The bicarbonate of soda is added to the mix and reacts with the opposing Ph value forcing a chemical reaction. Gas is released and the bread, cake or whatever it is goes up!

It tends to impart a flavour similar to buttermilk which can be quite attractive in some breads. The dough will only go up once so, proper dough conditioning that we get with yeast or sourdough based levains does not appear.

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 get used to baking bread by mastering one levain at first.

Preferably fresh or active dried yeast is the best way to get started in bread baking. Its a lot easier to learn all of the techniques of baking bread without the variables of pre-ferments and sourdoughs on top.

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

Adding a high amount of levain to a recipe is change three things, the flavour, aroma and the structure of the bread.

Typically, what will happen:

  • It will taste of it, possibly nice if it’s a sourdough, horrible if it’s yeast.
  • The rise is too quick which reduces the breads flavour development and gluten formation time.
  • It will rise erratically in the oven and can be responsible for holes in the bread crumb and rips in the crust.

Here's an article which gives a bit more insight on using too much yeast in bread.

Do levains go out of date?

Yes, fresh yeast is a living organism and will die. It’s best to look at the best before date on the packaging and make sure it gets kept in the fridge.

It can also go mouldy or dry out if exposed to moisture or air.

So kept it wrapped too. 

use a levain to raise bread

Dried yeast needs to be kept sealed so it doesn’t become oxidised. Fresh yeast needs to breathe at the same time we don't want to dry it could. The wax paper it comes in is usually best. Keep it in the fridge.

Out of date yeast which is still sealed in may still work. Spoon some into some tepid water and see if it bubbles sufficiently before risking it in your dough.

Unlike what you may have read, there's no need to do this every time. Just if there’s a reason that the yeast may be no longer active.

How to keep levains from dying

Yeast should be kept in the fridge, sealed. Fresh yeast needs to breath a little so I open the box everyday to have a bit of fresh air. A bit like having a pet!

Sourdough can die if not fed. When left alone it tends to go overripe and following that turns mouldy. It’s often possible to revive a sourdough by spooning a bit of the good stuff  and refreshing. After a couple of days of refreshments it will have reset itself and be good to use.

If using a rye or wholemeal sourdough, an over ripe, rancid smell and flavour can sometimes be irreversible. Starting again is the only option. But it’s worth trying to get it going again to preserve the flavour of an aged sourdough if you can.

Bicarbonate of soda can also go off. Despite my mum keeping her pot in the cupboard for years, it does degrade overtime. Once open, many bakers find it will only keep for 6 - 9 months before having to discard it. You can test by adding some to tap water and giving it a stir. If it bubbles up with plenty of carbon dioxide then your good. 

How much levain should I add to my dough mix?

There’s no golden rule, dense, harder grain breads need more leavin (or time) than lighter, white doughs.

These are what I tend to use as starting points when crafting a new recipe.

Fresh yeast 2%


Sourdough 20%

Maximum for fresh yeast is 2.5%, above 2.2 the taste of yeast is more noticeable in the bread. I don't generally go above 30% of sourdough. In cool climates without a proofer it may be an idea to increase this.

Can you make bread without a levain?

We could use flour, water and salt to make a bread, without a levain. The result would be like a flat bread. 

...Be a flat bread.

Breads like Pita, Naan and my salt less flat bread do use yeast to get a little rise and a lighter crumb. But there are a few flat breads that don’t call for any such as a tortilla.

Levain or Leaven?

Leavin is the French and more traditional way to spell it. Leaven is more acceptable in USA. As France gave the world many of the original bread recipes, such as Pain au leavin I prefer to use levain. Leaven is just as acceptable. Just not in France.

Tips on working with levains

So maybe you’ve learnt that every levain works slightly differently, imparting variations in flavour and structure extracted in fermentation. Also adding levains at different bakers percentages will also affect the quality of the bread.

Slow fermentation with a small amount of levain makes bread that has more flavour and dough conditioning properties.

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