A type of preferment used as a leavening agent for bread. This type of preferment specifically is originated in french cuisine. It is characteristic for its higher hydration (usually around 100%). It differs from the biga, which is a preferment originated in Italy.

A poolish consists of a mixture of flour and water with a very small amount of comercial yeast. This mixture is then let to rest and ferment for several hours (usually between 8 to 16 hours, depending on temperature and amount of yeast added).

One of the most important functions of a preferment is introducing acidity to the dough, which has several benefits to the overall quality of the final bread product.