Poolish vs. Biga: Pre-Ferments for Sourdough

Short answer: a poolish is a wet pre-ferment (100% hydration); a biga is a stiff one (50–60%). Both develop flavor before mixing the final dough. Sourdough already has a pre-ferment (the starter), so you may not need either — but they can add complexity for special bakes.

What pre-ferments are

A pre-ferment is:

• A small batch of flour and water with leavening
• Mixed hours before the main dough
• Allowed to ferment (4–18 hours)
• Added to the final mix

Pre-ferments add flavor and improve texture beyond what a same-day mix can achieve.

Common pre-ferments

Poolish

Poolish:

• 100% hydration (equal flour and water)
• Small amount of yeast (usually commercial)
• Ferments 8–18 hours
• Used for lean French breads

Recipe (for 1kg flour final dough):

• 200g flour
• 200g water
• 0.5g instant yeast (a pinch)

Mix and rest 12+ hours. Use in the main dough as part of the flour and water.

Biga

Biga:

• 50–60% hydration
• Small amount of yeast
• Ferments 12–24 hours
• Used for ciabatta and other Italian breads

Recipe:

• 300g flour
• 165g water (55%)
• 1g instant yeast

Mix into a stiff dough. Ferment 18 hours at room temp.

Why use a pre-ferment

Pre-ferments contribute:

• Complex flavor (acid byproducts)
• Improved keeping
• Better gluten development
• Open crumb

A same-day mix lacks this depth.

Sourdough vs. pre-ferments

Sourdough starter is essentially a permanent pre-ferment:

• Has wild yeast and bacteria
• Develops flavor over time
• Adds to the final dough

So sourdough already does what pre-ferments do for yeast bread.

Combining sourdough with pre-ferments

Some advanced recipes combine both:

• Sourdough levain + biga
• Adds extra fermentation depth
• More complex flavor
• More planning

For most home bakers, this is overkill. The sourdough starter provides plenty of flavor.

A sourdough biga experiment

If you want to try:

• Make a regular biga (with commercial yeast or part of starter)
• Use as 30% of the total dough
• Add to a sourdough recipe
• Compare to the standard sourdough version

You may notice extra wheaty depth.

When pre-ferments don't help sourdough

For most sourdough bakes:

• Pre-ferment is unnecessary
• Adds time without much benefit
• Sourdough starter does the same work

Skip pre-ferments unless you're chasing very specific flavor profiles.

A levain as a pre-ferment

Your sourdough levain (built the night before) is itself a pre-ferment:

• 100% hydration usually
• Made specifically for the bake
• Adds flavor to the dough

Most sourdough recipes already include this step.

Schedule with pre-ferment

For a sourdough + biga bake:

Day 1, 6 AM:

• Start biga (300g flour + 165g water + 1g yeast)

Day 1, 6 PM (12 hours later):

• Build sourdough levain

Day 2, 9 AM:

• Mix final dough using both biga and levain
• Bulk
• Shape
• Cold retard

Day 3, morning:

• Bake

This is a 2-day project for a deep-flavor bread.

Pre-ferments by bread style

For 90% of home sourdough, levain alone is enough.

A note on yeast in pre-ferments

Traditional recipes use commercial yeast in poolish and biga. Even sourdough recipes sometimes do this.

For pure sourdough:

• Use part of your starter as the pre-ferment yeast
• Just add starter to flour and water in the same ratio

This keeps the bread fully wild-leavened.

A simple takeaway

For most sourdough:

• Build a levain the night before
• This IS your pre-ferment
• It adds flavor and prepares yeast for the main dough

For exceptional bakes:

• Add a biga or poolish for extra depth
• Plan an extra day
• Compare to standard recipes

A final note

Pre-ferments are a topic that gets a lot of attention in baking books, but for most home sourdough bakers, they're not necessary.

Your starter already does what pre-ferments do.

If you want to experiment, try a biga for ciabatta or a poolish for baguettes. The extra step adds noticeable depth.

But don't feel obligated. Great sourdough doesn't require pre-ferments — just a healthy starter and good technique.