Poolish, biga and sponge do three different things to the same flour

The options around preferments in bread making are set out side by side below, with the conditions that genuinely favour one over the other.

What a preferment buys you

Fermenting part of the flour in advance gives that portion many hours of enzyme and bacterial activity before the main dough is even mixed. The result is more flavour compounds, more available sugar for crust colour and a dough with better extensibility.

It also lets you use a very small amount of yeast overall, since the preferment arrives already populated. None of this requires sourdough; a pinch of commercial yeast and twelve hours does most of the work. For a baker with a busy schedule, a preferment moves effort to the previous evening where it costs nothing.

Poolish

A poolish is made at 100 per cent hydration, equal weights of flour and water, with a very small quantity of yeast. At 20C it typically needs twelve to sixteen hours, and it is ready when domed and just starting to fall in the centre.

At oven temperature, the wet environment favours enzyme activity and produces a dough that is noticeably extensible and slightly slack. That extensibility suits baguettes, ciabatta and anything where you want an open, irregular crumb. Because it is liquid, a poolish is easy to mix by hand and easy to judge by eye.

Biga

A biga is stiff, usually 50 to 60 per cent hydration, and is torn into pieces rather than stirred into the final dough. The drier environment slows enzyme activity and favours acetic acid, producing a firmer, tangier, stronger result. Bigas are traditional in Italian baking for breads that need to hold structure at high hydration, such as ciabatta.

They tolerate longer fermentation without collapsing, and are more forgiving if you are two hours late using them. The trade-off is that they need a mixer or determined hands to break up into the final dough.

Sponge and pâte fermentée

A sponge sits between the two, typically at 60 to 75 per cent hydration, and is often used for enriched doughs. It ferments for a shorter time, sometimes only one to three hours, and is largely about giving the yeast a head start. Pâte fermentée is simply a piece of yesterday's fully mixed dough, salt included, saved and used the next day.

Because it contains salt it ferments more slowly and keeps better in the fridge, sometimes for two or three days.

It is the least fussy preferment available and costs nothing beyond remembering to hold a piece back.

Calculating the proportions

Preferments commonly hold twenty to forty per cent of the total recipe flour, with the rest added at final mix. More prefermented flour means more flavour and faster final fermentation, but also a weaker, more extensible dough.

Above about half the flour, most doughs become too slack and acidic to shape well. Remember to subtract both the flour and the water in the preferment from the main recipe totals. Writing the whole thing in baker's percentages makes this arithmetic trivial rather than error-prone.

Flour absorbs water differently by brand and by season; hydration is a target, not a rule.

Judging readiness

A preferment is at its best when it has peaked and is just beginning to recede, showing a slightly sunken centre. Used too early it contributes little; used many hours late it is acidic and can weaken the final dough.

In the tin, temperature is the main control, so a cooler room means less yeast is needed for the same overnight window. As a rough guide, halving the yeast roughly doubles the time needed at the same temperature. Keep a note of yeast quantity, room temperature and hours, and you will hit the window every time within two attempts.

Side by side

The takeaway

Ferment a fifth of the flour the night before and the loaf improves without any extra skill.

Patience is an ingredient, and it is the one people leave out.