How does a levain make bread rise?

A levain is an ingredient that’s added to dough to make bread rise. Once understanding the differences between the levains available to us it opens up new possibilities in bread making.

How different levains make bread rise is shown with examples in the how to bake bread course that's coming soon. 

But in the mean time I thought I'd write this post to explain what happens when different levains get to work.

Understanding yeast and other levains is essential to learning to become an artisan baker, we get that yeast makes bread rise, but actually goes on?

And what other levains are available? 

The point of a levain

Usually at the start of mixing the chosen levain is added to the dough ingredients and develops the flour. Once in contact with water and flour, fermentation begins.

During this period the doughs structure develops and rises before it’s ready for the oven.

Fermentation starts once the ingredients combine and continues until the heat of the oven ends the process.

Starch from the flour is turned into carbon dioxide and ethanol, whilst protein from the flour is softened by the water forming a gluten structure.

Check out this guide on dough fermentation afterwards, it explains every step in detail. 

A definition of a levain

An active ingredient who’s core responsibility is to create gas, the secondary is developing flavour and keeping qualities.

Typically a levain is introduced to the dough ingredients at the start of doughs process. It’s mixed slowly at first to incorporate and gets to work straight away.

Changing the levain or altering its ratio to the flour will alter the characteristics of the bread.

Yeast is the most common levain, especially for new bakers. But there are others available. 

What are the different levains that bakers use?

As are a few types, including a few varieties of each, I’ve listed them first and I’ll go into them in more detail afterwards.

Understanding how each of them work to ferment the dough will assist you in bread making.

It’s important to understand that in all cases fermentation of the flour works alongside the levains fermentation.

During this a gluten network develops from which retains gas produced in the dough. Here's a list of levains:

  • Fruit
  • Commercial bakers yeast
  • Dried fast action yeast
  • SAF yeast
  • Sourdough
  • Pre-ferments like, biga, poolish or pâte fermentée
  • Bicarbonate of soda 


This was one of the earliest forms of levain, and still used today in the production of alcohol.

Certain fruit combine with natural levains found in the air or on the fruit surface to raise bread. 

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In the case of alcohol, the sugars and the yeast are obtained from the same fruit. In others an extra amount of yeast and sugar are added for bubbles, extra alcohol and flavour.


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 derived from waste parts of sugar beet.

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 yeast is fed and regrows. 

Yeast reacts with the starch in the flour by breaking down the sugars found and turning them into ethanol and carbon dioxide.

The gluten doesn’t let much gas out, unless forced by hand or machine. The retained gas pushes the dough up commonly called rising.

The ethanol that resides alters the acidity (ph factor) to develop flavour and colour in the crust. Using a small amount of levain usually results in a slow fermentation time.

This creates a stronger, more elastic crumb structure.

Using more yeast gives a brighter, but less flavoursome bread.

Artisan bakers prefer to have a slow fermentation to give intensity to the bread that’s otherwise not possible. 

Dried yeast

When bakers yeast combines with hydrated flour it gets to work straight away.

It’s alive, it’s happy and it’s being fed, no worries. But when using dried yeast, it’ll take a few more minutes to get going. 

It’s necessary to rehydrate the yeast which kicks it into action.

Some bakers prefer dried yeast to the fresh stuff for this reason.

It gives gluten development a head start and increases the overall fermentation time.

Other bakers like me can’t get their head around it and prefer to use fresh bakers yeast every time. 

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!!

….It does takes longer, and. is likely to drying out and skin up…. but it will get their.


In fact, if the right conditions of warmth, time and moisture are made for the it then the slow fermentation is likely to lead to a superior loaf.

Pizza doughs are typical of this where a big batch of dough is fermented for 24 hours with a tiny pinch of yeast.

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

Biga & Poolish

These are types of preferment or sometimes called a starter.

They take a small amount of yeast and maximise the potential of it by fermenting it in flour and water.

Preferments also create structure in the dough, from flour fermentation.

To make a biga or poolish, a little yeast is added to flour and water and given a gentle mix by hand. 

Biga used to make bread rise

It’s covered and left for 4 to 18 hours. The preferment expands in the bowl and forms the levain.

The end realist is a vibrant and structured levain. 

For a longer fermentation we can use less yeast, water (in a biga), or cool it.

We add it to our bread dough when it’s ripe. as our levain. Using a pre-ferment means a few things will happen:

  • The flour gets broken down gently by the water allowing the best possible platform for gluten development. This is great for heavily aerated doughs like Ciabatta and Focaccia, the dough structure is strong and holds a lot of air.
  • An more intense flavour as the flour gains a sweet taste from complex starches being drawn out of the grain.
  • The crust of the loaf becomes darker due to an increase in natural sugars.
  • The less the bread will taste of yeast, the more the flavour of the flour will be released. 

Using a biga or poolish when it’s ripe can take a bit of getting used to. Under ripe and the bread won’t have the lightness given from the strong gluten structure. 

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

The difference between a biga and a poolish

The poolish is originally from Poland, but it was adopted by the French into many of their breads. It uses equal quantities of flour and water.

Whereas the Italian biga, can be adapted to make stronger pre-ferments by adding less water.

This is perfect for generating extra flavour from the lighter tasting flour that’s produced in the country. 


This works differently to yeast. But sourdough, like yeast is a living organism. It preys on feeds of flour and water to stay alive.

A mix of flour and water, left to ferment by naturally occurring yeasts is refreshed every day with more flour and water and used by bakers as a levain

The sourdough absorbs yeasts and aromas from the air in which it grows. 

Naturally occurring yeasts which activate the sourdough are available in the air or the flour it’s made from.

This creates a unique flavoured levain every time.

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 after around 7 days 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, honey or yogurt to help get the sourdough started which arguably adds some extra flavours.

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, but why is it so good?

If you would like to know more about how sourdough is made, then take a look at the how to bake bread course.

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How does Sourdough work differently to yeast?

Yeast works by reacting with starch to create gas and alcohol. Sourdough works by having an off balance acidity (Ph factor) which reacts with an opposing Ph factor of the dough mix.

The result of the combination is the creation of gas and lactic acid.

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

Similarly to the biga or poolish method, the bread absorbs the levains structure.

how does a levain make bread rise

The more hours the pre-ferment has been left to build, the stronger the gluten arrangement and aroma will be.

Instead of a few hours, a sourdough starter can often be years if not centuries old.

An irregular holey texture is often found in a sourdough bread, that’s just sort of bread that I love to rip off and dip into extra virgin olive oil.

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.

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 a 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. 

A bit of fresh yeast is often added to maximise the raise.

Or, re-hydrate in a poolish, leave for 12-18 hours and use it the following day.

This way maximises the power of the levain, but a bit more "proper".

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Bicarbonate of Soda

I’m no bicarb expert sadly. But I can share with you how it works, it’s similar to sourdough.

A reaction happens as two opposing Ph factors combine once the bicarbonate of soda is added to the mix. 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. 

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 yeast as its a lot easier to learn all of the techniques of a baker at first without the variables of catching pre-ferments or sourdoughs at the optimum time as well. 

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.

There's an article which gives a bit more insight on whether it’s a good idea to use less yeast. 

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. Out of date yeast which is still sealed in the original wrapper 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 read, there's no need to do this every time, just if there’s a reason the yeast may not be longer active.

How to keep other types of yeast from dying

SAF yeast should be kept in the fridge. Most dried yeasts will last longer in a cooler temperature too, providing it’s properly sealed.

Sourdough can die if left alone, it tends to go overripe and following that becomes mouldy.

It’s often possible to revive a sourdough by spooning a bit of good stuff out and refreshing it.

After a couple of days, it will have reset itself.

If using a rye or wholemeal sourdough, an over ripe, rancid smell and flavour can sometimes be irreversible.

So 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.

Even if it's just a little addition to the fresh sourdough starter.

When a biga, polish or pate ferment gets left for too long it turns over-ripe and will lose its structure.

It can still raise the bread, but it won’t have a nice structure or flavour. 

Leave longer than over ripe and the yeast dies from starvation and it will have to be thrown away.

Bicarbonate of soda can also go off. Despite my mum keeping her pot in the cupboard for years, it does degrade overtime.

Once open, most serious bakers will only keep it for 6 - 9 months before discarding 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%

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 flatbread. 

This would be a flatbread.

Breads like Pita, Naan and my saltless flatbread do use yeast to get a little rise and a lighter crumb.

But there are a few flatbreads that don’t call for any such as a tortilla

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 different ratios in the bakers percentage of the recipe will also affect the quality of the bread.

Slow fermentation, using a small amount of levain is typically favoured.

For more information, recipes and a course on how to bake artisan bread properly then check out the how to bake bread course.