Poolish, biga, sponge: what they do and when

A pre-ferment is a small portion of flour, water, and yeast mixed hours before the main dough, left to ferment overnight, then incorporated when you mix the rest. It's the simplest technique for adding sourdough-like depth to commercial-yeast bread without keeping a starter alive.

Three variants come up most often: poolish, biga, and what English-speaking bakers call "sponge." The mechanics are similar; the differences are in hydration and origin.

Why use a pre-ferment

A 12–18 hour pre-ferment gives the bread three things a same-day yeasted dough doesn't have:

1. 1.More flavor. Long fermentation produces aromatic compounds (organic acids, alcohols, esters) that no fast-fermented dough can match. Even a small portion of pre-ferment in the final dough shifts the flavor noticeably.
2. 2.Better structure. Extended fermentation in the pre-ferment develops gluten passively. The final dough is stronger from the start, needs less mixing, and handles better.
3. 3.Improved keeping. Pre-fermented breads stale slower. The acids produced during the long ferment slow the staling reactions in the finished bread.

All three benefits at the cost of mixing a small bowl of flour and water the night before. The active time added is about 90 seconds.

Poolish

A liquid pre-ferment at exactly 100% hydration (equal weights of flour and water) with a tiny amount of yeast. French in origin, popularised in modern artisan baking by bakers like Lionel Poilâne.

What it looks like ready: bubbly, slightly domed surface, smells like yeasted beer and apples. If it's collapsed flat or smells sharply alcoholic, it's gone past peak: still usable but the bread will be slightly tangier than intended.

Best for: baguettes, pizza, ciabatta. Doughs where you want lighter, more open crumb and milder flavor.

Biga

A stiff pre-ferment at roughly 50–60% hydration. Italian in origin, traditionally used for ciabatta, pizza in teglia, and rustic Italian breads. Drier than poolish, with a longer shelf life and a different flavor profile.

What it looks like ready: surface should look slightly bumpy with visible gas pockets when broken open. Smell should be mildly nutty and fermented, less aggressive than poolish. A biga past peak deflates into a dense, sharp-smelling mass.

Best for: ciabatta, focaccia, rustic Italian loaves, pizza in teglia. The lower hydration produces a different acid balance: biga tends toward more lactic, less acetic, giving a milder but rounder flavor than poolish.

Sponge

Sponge is the umbrella English term for a generic pre-ferment, traditionally used in commercial sandwich bread and brioche. Hydration varies, anywhere from 60% to 100%. The term is used loosely in English-language baking books.

Practically, a "sponge" in most modern recipes means whatever hydration the recipe specifies. If it's around 100%, it's a poolish by another name. If it's stiffer, it's effectively a biga. The formula matters more than the label.

How to incorporate the pre-ferment

On bake day, the pre-ferment becomes one of the ingredients in the main dough. The standard process:

1. 1.Calculate the rest of the formula. Subtract the flour and water already in the pre-ferment from the totals. Example: a 500 g flour formula at 70% hydration with a 100 g poolish: the main dough adds 400 g flour and 250 g water (350 g total water minus 100 g already in the poolish).
2. 2.Combine all ingredients in the mixing bowl. Add the pre-ferment as one component. It's wet enough that it incorporates fast.
3. 3.Mix as normal. The dough comes together faster than a same-day dough because part of it is already developed.
4. 4.Bulk and final proof. Use a reduced yeast amount in the main dough; the pre-ferment is contributing its own active yeast. A typical adjustment: drop the main dough's yeast by 40–60% relative to a same-day recipe.

Picking the right pre-ferment percentage

Most pre-ferment recipes use 15–35% of the final flour weight in the pre-ferment. Higher percentages produce more pronounced fermented flavor.

• `10–15%`: subtle effect. Bread is slightly improved but easy to mistake for a same-day dough.
• `20–30%`: the sweet spot for most home baking. Clear flavor improvement without dominating.
• `30–40%`: strong pre-ferment character. Suitable for ciabatta, country breads, focaccia.
• `40%+`: the pre-ferment is the dominant flavor. Used for very specific styles (some baguette traditions, certain Italian breads).

Common pre-ferment mistakes

Letting it go too long

A poolish or biga at room temperature past 18 hours starts collapsing. The yeast has consumed most of the available sugars, gas production stops, and the gluten begins breaking down. Use it within 12–16 hours of mixing.

Too cold a kitchen

Below 18 °C / 64 °F, fermentation slows enough that 12 hours isn't enough. The pre-ferment will look barely-active when you go to use it. Either keep it in a warmer spot, increase the yeast slightly (up to 0.2%), or let it ferment longer.

Forgetting to adjust the main dough's yeast

Using a full yeast amount in the main dough on top of a fully-active pre-ferment over-ferments the final bread. Reduce the main dough's yeast by roughly half when using a meaningful pre-ferment percentage.

Using a pre-ferment past peak

If your poolish has collapsed into a flat puddle and smells aggressively alcoholic, the bread will taste sharper than intended. It'll still be edible, just tangier and slightly less risen than expected.

Pre-ferment vs sourdough levain

A sourdough levain is technically a pre-ferment: same general role, mixed the night before, contributing flavor and structure. The difference: a levain uses wild yeast and lactobacillus from a maintained starter, while poolish/biga use commercial yeast.

Practical implications:

• Levain has more complex flavor (both sour and aromatic) because of the bacterial component. Poolish/biga are mostly clean yeast flavor with depth.
• Levain is more variable. Depends on starter health, temperature, feeding history. Poolish/biga are predictable.
• Poolish/biga work for any home baker. No starter needed, no maintenance commitment.

Many modern professional bakeries use both: a sourdough levain for character, plus a small commercial-yeast poolish for additional consistency and lift. For home baking, pick one or the other based on whether you want to maintain a starter.

The takeaway

Mix 100 g of flour, 100 g of water, and a pinch of yeast the night before. The next morning, use it as part of your bread recipe. The bread will be noticeably better than its same-day version. The cost: 90 seconds of active time, one extra bowl, and the discipline of starting the night before.