When you set out to bake bread, you are immediately faced with a decision: How do I make the dough? There are two methods: straight dough and preferment. (We’ll leave sourdough to another day.)
Straight dough means that you have assembled the ingredients for the bread and made the bread without any interruption; you went straight-through from start to finish. Used properly, this method will yield very good bread. It’s what most people think of when they think about making bread. There is another way to make bread: use a preferment kefir grains.
A preferment, as the name implies, is mixing a portion of the flour, yeast and water to begin the work of fermentation before the main mixing. The goal is to unlock all or most of the flavor of the flour by letting the yeast and flour develop for several hours or even days. There are four types of preferments: old dough, sponge, biga and poolish.
Old dough is merely a portion of a batch of dough that is saved and incorporated in the next batch. If the dough is four pounds, you might remove six or eight ounces of the dough, save it in the refrigerator or freezer, and use it in the next batch of bread. This method is mainly used when the baker is baking the same bread on successive days.
The sponge method is mixing all the water and yeast and half the flour, then letting it develop for a half hour or a few hours. The sponge will be a loose batter that will bubble and expand. When the sponge is ready to use, the baker adds the rest of the ingredients and continues making the bread according to the recipe.
A biga is an Italian preferment. Different traditions have different recipes for a biga, but we will use the classic definition, a rather stiff dough, around 60% hydration (The water weighing 60% of the weight of the flour) and a small portion the yeast. This dough is allowed to develop for a period of time, anywhere from a few hours to a day or two, then incorporated into the dough. I use longer prefermentation times for a biga than for the other methods. I think the relatively low hydration allows the yeast to continue to find nutrients to work on for a longer time than would be the case in the others. This is subjective; I encourage you to experiment and see what works for you. Some Italian bread recipes specify a biga that is 100% hydration, which makes it a poolish, but who’s keeping score?
A poolish is similar to a biga, but made at a higher hydration, usually 100%; equal weights of flour and water with a small bit of yeast. This mixture is allowed to develop for a few hours, then used in the dough. I have developed poolishes overnight and even for two days and they have been good, but I prefer to limit them to eight to ten hours.
One thing to remember is that we are not using these for their leavening power, but for the flavor they add to the finished loaf. These may rise and fall, but that doesn’t really matter. What does matter is that the fermentation process gets a head start and contributes a lot of flavor to the dough and the bread.