Mineral oil saturated (MOSH) and aromatic hydrocarbons (MOAH) are environmental and processing contaminants also found in extra-virgin olive oil. Knowledge on contamination sources can help minimize them. The main objective of this work was to investigate the impact of milling operations. To this purpose, samples from 25 processing lines (at 5 different processing stages) were analyzed by online high-performance liquid chromatography—gas chromatography—flame ionization detection. A protocol for eliminating endogenous n-alkanes was tested and applied when necessary. Generally, transport to the mill had a negligible impact. The washing step had a mitigation impact, more evident on samples with higher contamination. On average, total MOSH decreased of 2.1 mg kg–1. Despite the reduction determined by washing, the entire milling process resulted in an increase in contamination (> 30%) for 20% of the processing lines. Total average MOSH and MOAH contamination increased by 2.3 and 0.6 mg kg–1, respectively. Practical Applications: This work aims to improve the knowledge on the presence and sources of mineral oil hydrocarbons (MOH), contaminants of petrogenic origin, in extra-virgin olive oil. In particular, this work investigates the impact of processing at the mill, including the transport stage, as well as the potential of the washing step in reducing the contamination. For the first time, a systematic study on this topic has been carried out. The knowledge of the contribution of individual steps in the production process to final product contamination is of paramount importance in identifying critical points on which to take action to mitigate contamination, and this is of great interest for all operators of the sector and for protecting consumer health, especially when considering possible presence of MOAH, which may include genotoxic and carcinogenic compounds.
