Allergy to hazelnut seeds ranks among the most prevalent food allergies in Europe. The aim of this study was to elucidate the gastrointestinal digestion of hazelnut allergens on molecular level. Hazelnut flour was digested in vitro following the Infogest consensus model. For six allergenic proteins, the time-dependent course of digestion was monitored by SDS-PAGE and HPLC−MS/MS, and degradation products were characterized by a bottom-up proteomics approach. Depending on the molecular structure, a specific biochemical fate was observed for each allergen, and degradation kinetics were traced back to the peptide level. 1183 peptides were characterized, including 130 peptides that carry known IgE-binding epitopes and may represent sensitizers for hazelnut allergy. The kinetics of peptide formation and degradation were determined by label free quantification and follow a complex multi-stage mechanism.