In a 1 1/2 quart glass or earthenware container. Mix together 1 envelope dry yeast with 2 cups warm water and 2 cups all-purpose flour; cover with a cheesecloth (this lets air-born wild yeasts make contact). Leave in warm room 48 hours. Stir 2 to 3 times. It will ferment and bubble and have a slightly sour smell. This makes 3 cups. To use, stir and pour off as much of the starter as the recipe requires. Add equal parts of flour and water (2 cups each) to the remaining starter in the pot. Stir and let stand a few hours until it bubbles again before covering and refrigerate. By doing this, you can keep it going continuously. Never add anything but flour and water to the starter pot.