What is dough starter?
For yeast-based doughs such as bread dough, a starter usually
consists of yeast, sugar, water, and a small amount of the flour
you'll be using in the finished baked good. This is sometimes
referred to as a sponge. Sourdough bread is usually created using a
starter like this. Some people keep their sourdough starter going
for months or even years, since yeast are a living plant. They
store the starter in the refrigerator, and replenish it with
additional components as needed.