Classifications
In general, there are two pre-ferment varieties: sponges, based on baker's yeast, and the starters of sourdough, based on wild yeasts and lactic-acid bacteria. There are several kinds of pre-ferment commonly named and used in bread baking. They all fall on a varying process and time spectrum, from a mature mother dough of many generations of age to a first-generation sponge based on a fresh batch of baker's yeast:
- Biga and poolish are terms used in Italian and French baking, respectively, for sponges made with domestic baker's yeast. Poolish is a fairly wet sponge (typically made with a one-part-flour-to-one-part-water ratio by weight), whereas biga is usually drier. Bigas can be held longer at their peak than wetter sponges, while a poolish is one known technique to increase a dough's extensibility.
- Old dough (pâte fermentée) may be made with yeast or sourdough cultures, and in essence consists of a piece of dough reserved from a previous batch, with more flour and water added to feed the remaining flora. Because this is a piece of old dough, it has the typical ingredient of salt to distinguish it from other pre-ferments. Once old dough had rested for an additional 10 hours of age, the French named it Levain de Chef.
- Sourdough starter is likely the oldest, being reliant on organisms present in the grain and local environment. In general, these starters have fairly complex microbiological makeups, the most notable including wild yeasts, lactobacillus, and acetobacteria. They are often maintained over long periods of time. The Boudin Bakery in San Francisco for example, has used the same starter dough for over 150 years. A roughly synonymous term in French baking is levain.
- Mother dough often refers to a sourdough, and in this context the term starter often refers to all or a piece of mother dough; however, mother dough may also refer to a first-generation yeast sponge; so the process used in relation to the ingredients and fermentation times is important to understanding yeast versus sourdough methods. A roughly synonymous term used in French baking is Chef.
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