Well, the longer you leave it, the hotter it gets. It's a left foot- right foot process, for me. I take the lid off and just whiff, now and again, until I can smell the right heat, usually when my eyes water. Then, I add vinegar to stop the heat. You can always cut it later, when you use it in food. Each horseradish root, depending on how it was grown, can create a different heat. Have to smell the process.