Once it is properly fermented, the dough can be stored in the refrigerator indefinitely as long as it is replenished every two weeks by adding equal parts flour and water.
In a large mixing bowl, combine yeast and the water; let stand until yeast is dissolved and bubbles form on the surface, about 5 minutes.
Stir in buttermilk, sugar, and 1 1/2 cups flour. Cover with a kitchen towel, and let stand in a warm place 24 hours. Whisk in another 1/4 cup flour until it is well combined. Set aside, covered, another 24 hours before using or storing in a jar or airtight container.
You can use two cups starter instead of one package active yeast in most bread recipes.