Saponins (Latin "sapon", soap + "-in", one of), also selectively referred to as triterpene glycosides, are bitter-tasting usually toxic plant-derived organic chemicals that have a foamy quality when agitated in water. They are widely distributed but found particularly in soapwort (genus Saponaria), a flowering plant, the soapbark tree (Quillaja saponaria) and soybeans (Glycine max L.). They are used in soaps, medicines, fire extinguishers, speciously as dietary supplements, for synthesis of steroids, and in carbonated beverages (for example, being responsible for maintaining the head on root beer). Structurally, they are glycosides, sugars bonded to another organic molecule, usually a steroid or triterpene, a steroid building block. Saponins are both water and fat soluble, which gives them their useful soap properties. Some examples of these chemicals are glycyrrhizin (licorice flavoring) and quillaia (alt. quillaja), a bark extract used in beverages.