Scrap dough is simply a piece of fermented bread dough saved from a previous batch. It is sometimes known as pâte fermentée (pot fer mawn tay), meaning “fermented dough.” Saving a piece of fermented dough, preferably in the retarder so it doesn’t overferment, is an easy and common way to get the benefits of using a pre-ferment without having to make one separately. Of course, it is also possible to make a batch of bread dough just to use as a pre-ferment.
Because scrap dough is actually bread dough, it differs from other ferments in that it contains salt as well as flour, water, and yeast. The salt slows the fermentation. To balance the salt, a scrap dough contains more yeast than the other types of pre-ferments we have discussed.