Start the poolish the day before or at least 12-18 hours before baking: In a medium bowl, mix 75 g wheat flour type 550, 75 ml water, and 1 g fresh yeast until well combined and no dry flour spots are visible.
Loosely cover the bowl with plastic wrap or a damp cloth and let the poolish ripen at room temperature for 12 to 18 hours. It should form bubbles and smell slightly yeasty.