How does a person mix-up potassium sorbate and yeast? Potassium sorbate kill yeast, right? So you might think that this guy made himself $150 grape juice. Guess again. He actually was able to save his wine and he learned a lot about potassium sorbate. Apparently potassium sorbate is more effective the higher the alcohol content. So it take more to prevent grape juice from fermenting, then it does to prevent wine from fermenting.