Proteomic identification of beer brewing products in the ground layer of Danish Golden Age paintings

The application of mass spectrometry-based proteomics to artworks provides accurate and detailed characterisation of the protein-based materials used to produce them, which is highly valuable to plan conservation strategies and reconstruct the artwork’s history. In this work, the palaeoproteomic analysis of canvas paintings from the Danish Golden Age led to the confident identification of cereal and yeast proteins in the ground layer. This proteomic profile points to a (by-)product of beer brewing, in agreement with local artists’ manuals. The chronology of the artworks featuring this unconventional recipe allows us to conclude that it was used by the workshops within the Royal Danish Academy of Fine Arts. The mass-spectrometric dataset generated from palaeoproteomics was also processed with a metabolomics workflow. The spectral matches observed further supported the palaeoproteomic conclusions, and, in at least one sample, suggested the use of drying oils. These results highlight the value of untargeted proteomics in heritage science, correlating unconventional artistic materials with local culture and practices.