A thermometer is by far the best tool for the job (and it's handy for plenty of uses!), but if you don't have one, here's how to know if it's ready. Using a spoon, drop a small amount of caramel into a glass of cold water. Leave it in for a few moments to cool, then pick up the ball of caramel. If it is at the soft ball stage, it should be pliable and slightly sticky in your hands.