Sanitary valves are designed for use in applications requiring clean or sterile processing. In order for a valve be considered sanitary it must NOT have crevices or cavities that can trap media which bacteria can feed on and multiply. The wetted surfaces (that contact the process media) must be polished and radiuses must be of a minimum size to avoid media clinging or entrapment. While plastic, brass, and other materials are acceptable for use in sanitary applications, stainless steel is preferred by most.  See below for more info: