In many countries plastic bottles made of PET (polyethylene terphthalate) are used as refillable beverage containers. Unlike glass, PET bottles are lightweight, unbreakable as well as easy to transport. However, PET is not tasteless. Decomposition products such as acetaldehyde can enter the beverage and have an unpleasant taste effect even in small quantities. In addition, refillable PET bottles must be cleaned at significantly lower temperatures than glass, which facilitates the retention of potential contaminants. Common contaminants include fuels, detergents, or hazardous solvents that get in through improper handling of the containers. To avoid both potential health hazards and bad taste, bottlers of refillable PET containers must therefore be able to eliminate contaminated bottles from the filling process by identifying them.