campden tablets are used by people making their own beer, wine, or cider. the tablets kill yeast, making better yeast to be added later for better drinks. 5 of them in 1 pint of water makes a cleaning liquid that can be used to clean the equipment. they are made from sulfur. they were invented in gloucestershire in the 1920s, but boots co. made them better. they can also be used to get rid of chlorine in tap water, making it safer to drink.