Star San is an acid based sanitizer that is quick, odorless, tasteless, and safe for most materials except softer metals. Use of 1 oz of Star San per 5 gallons of water and a contact time of 1 minute makes Star San very economical and convenient. Any foam that is left over in your carboy or keg from the Star San solution will not harm your beer or you, and is perfectly safe and non-toxic, nor will it impart any flavors or odors. If you plan on making some up for spray application it is best to use distilled or RO water to maximize the life of the unused portion (minerals in tap water reduce the shelf life of Star San once in solution). If a lower foaming alternative is preferred, checkout Saniclean.