an inspection system for sampling and determining the presence of residues of contaminants within plastic materials to be recycled from used plastic materials such as plastic beverage bottles or plastic food containers includes a chemical sniffing apparatus , or alternatively an optical scanner , for detecting the contaminants as the plastic materials are rapidly moved along a conveyor past a series of stations . recycled food or beverage bottles are fed through a shredder in - line with the conveyor and the shredded plastic material from the bottles is fed to a washer . the bottles and shredded material may be tested for contaminants at any location in an in - line process . in one exemplary system first the bottles are tested prior to entry into the shredder in order to remove bottles containing gross contaminants . second the shredded material emerging from the shredder is immediately tested for contaminants at an elevated temperature caused by the shredding process and contaminated materials are separated or sorted out from the uncontaminated material . third , the materials are again tested for contaminants as they emerge from the washer once again taking advantage of the elevated temperature of the materials which is conducive to the emission of vapors of the contaminants . contaminated materials are again sorted from the uncontaminated supply of materials to be used for the fabrication of new plastic food or beverage bottles .