Stir the yeast into the warm water & let proof for 10 minutes. Stir in the remaining water & then the flour, 1 c at a time. Mix with a wooden spoon for 3 or 4 minutes. Leave the biga in the mixing bowl. Cover with plastic wrap & let it rise at cool room temperature for anywhere between 6 & 24 hours. The starter will triple in volume & then collapse a bit. It will also be wet & very sticky when it is ready to be used. Cover & refrigerate if not using at once. To use the biga, scoop out the needed amount while it is cold.