It can occur that consumers fill PET bottles for beverages with solvents, fuels, and other substances that are harmful to health. If such contaminated PET bottles end up being recycled (PCR PET), harmful compounds can escape from the flakes. During the recycling process, the PET bottles are cleaned and shredded into flakes, after which they are available as raw material for further use. Quality control of PET flakes requires a measurement method that can quickly examine PET flake batches and immediately determine characteristic impurities so as to prevent low-quality material from entering further production steps.