PTC Paper, Phenylthiocarbamide (PTC), also known as phenylthiourea (PTU), is an organosulfur thiourea containing a phenyl ring. PTC has the unusual property that it either tastes very bitter or is virtually tasteless. This depends on the genetic makeup of the taster. The ability to taste PTC is often treated as a dominant genetic trait. About 70% of people can taste PTC.