Use King Arthur Flour's fresh sourdough starter by adding unbleached all-purpose flour and water to "feed" the starter within 24 hours of receiving it. The process repeats adding flour and water several times until the sourdough starter is ready for use.
To prepare the starter, add 1/4 cup of lukewarm water to the container, and stir to dislodge the starter and combine. Pour the starter into a large bowl, and then add 1 1/4 cups of lukewarm water and 2 cups of unbleached all-purpose flour to the mix, stirring well to combine. Cover the bowl with plastic wrap, and allow to sit at room temperature for eight to 12 hours.
When the starter appears bubbly, stir the starter again and discard half. Mix in 1/2 cup of lukewarm water and 1 cup of flour. Stir until the mix resembles thick pancake batter. Cover the bowl again, and let sit at room temperature for another two to four hours until it appears bubbly. Stir the starter again, discard half, and feed the reserved half with another 1/2 cup of lukewarm water and 1 cup of flour.
Mix the batter, allowing it to be slightly thick and lumpy. Let sit at room temperature for another two to four hours, stir the starter down, place it in a loosely lidded stoneware or glass container, and place it in a refrigerator until ready to use. Mix the starter into batter and dough for breads, waffles, pizza crusts, biscuits and pancakes.