Platinum Instant Sourdough: Yeast + Sourdough Culture is a unique, all-in-one packet solution that combines our original Platinum Yeast formula with a real, dried sourdough starter. Using our sourdough yeast, there’s no need to maintain a sourdough starter! Contains a premium instant yeast, giving a consistent rise to all your baked goods. Plus, there’s no need to proof the yeast; simply add it to your flour and other dry ingredients.