Biga is a yeasted starter, the equivalent of France's poolish. Don't be scared off by making a starter: it takes less than 5 minutes and adds so much character to bread. The crust will be crunchier, the crumb moister, and the bread more flavorful-plus, the bread will have a longer shelf life. To make it easier to get the biga starter out of the measuring cup, oil the inside of the cup lightly; that way the starter will slip right out of the cup. The recipe below yields 28 ounces of starter, enough for 1 recipe of Rustic Italian Bread.
Dissolve the yeast in 13/4 cups (14 ounces) of very warm water (105° to 115°) in a medium bowl. Add the flour and stir vigorously with a wooden spoon or your hand for 2 to 3 minutes, or until a smooth, somewhat elastic dough has formed. The starter will be thick and stretchy. It will be softer and more elastic after it has risen.
Scrape the starter into a clear container with high sides and cover with plastic film. Mark the height of the starter and the time on a piece of tape on the side of the container so you can see how much it rises.
At this point you have two options. If you plan to make the dough later the same day, let the starter rise at room temperature until it has risen to the point where it just begins to indent on top; this may take 6 to 8 hours. It will triple in volume and very small dents and folds will begin to appear in the top of the surface as it reaches its peak and begins to deflate. It is important that you use the starter before it sinks too much.
If you are not planning to make the dough until the following day, let the starter rise for 1 hour after mixing it, then place it in the refrigerator and let it rise there for at least 14 hours before taking it out to use as described in the recipe. Compensate for the cold temperature of the starter by using warm water (85° to 90°) instead of the cool water specified in the recipe when mixing the Biga into the dough. Or let the starter sit out, covered, until it reaches room temperature (this may take several hours). Then mix the dough, let it rise, shape it, bake it, and enjoy!