Biga
A biga is a stiff Italian preferment, usually at 45–55% hydration, with a small amount of yeast. Unlike the liquid poolish it comes together firm and barely sticks to the hands.
The low moisture holds back the lactic acid bacteria and tilts fermentation towards the yeast, so a biga tastes less sour and more sweetly nutty than a poolish. The firm structure also preserves gluten strength better, which helps with ciabatta and other breads that want a large, irregular crumb.
A biga is mixed 12–18 hours before the final dough, often kept cool. When ready it has grown in volume, gone webbed inside and smells ripe and faintly winey.