1Put the yeast in a small bowl, add the warm water, and whisk vigorously for 30 seconds. The yeast should dissolve in the water and the mixture should foam. If it doesn't and the yeast granules float, the yeast is "dead" and should be discarded. Begin again with a fresh amount of yeast and water.
3With the mixer running on the lowest speed, pour in most of the icewater, reserving about 2 tablespoons, followed by the yeast-water mixture. Pour the reserved water into the yeast bowl, swirl it around to dislodge any bits of yeast stuck to the bowl, and add to the mixer. Mix for about 15 seconds, stop the mixer, and add the poolish or tiga.