One potential fraud is the undeclared bulking of meat products such as burgers and sausages with cheaper plant-based ingredients. The authors of this paper (purchase required) describe a rapid (20 hours), robust and sensitive method for the detection of 23 foreign protein sources (alfalfa, buckwheat, broad bean, chia, chickpea, coconut, egg, flaxseed, hemp, lentil, lupine blue, maize, milk, pea, peanut, potato, pumpkin, rapeseed, rice, sesame, sunflower, soy, and wheat) in meat products using high performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS). It includes a new rapid defatting procedure, without carry-over effect and suitable for routine analysis, a robust protein extraction protocol (TRIS/HCl (1 M, pH 8.2) with 40% acetonitrile), suitable for various animal- and plant-based proteins including grain proteins, and new peptide markers for buckwheat and potato. An investigation of the influence of cooking (emulsion-type sausages), grilling (hamburger patties) and maturation (salamis) showed that the detection method is robust against different types of processing. The authors report that the limits of detection for all foreign protein sources were ≤ 0.02% protein and that no false-positive or -negative results were obtained.