The pitch deposits formation affects largely the pulp mill’s productivity as this bring unwanted manufacturing problems, for example operational downtime, increased maintenance costs, and compromised quality of the final product. With the limited understanding of chemical profile of pitch deposits [1-5] and the increasing demand of mill’s water circuit closing and energy self-sufficiency, we urgently need a better understanding about the formation mechanism of the pitch deposits, which is currently hampered by the lacking knowledge about mass flow of the wood extractives (and its secondary forms) inside the entire fiberline, including the pulp, pulp liquids, looped liquids as well as pitch deposits. The study explores the behavior of extractives in eucalyptus wood during the pulping and bleaching process, with a focus on their role in pitch deposits formation. For the first time, a comprehensive analysis was conducted on pitch deposits, pulp, pulp liquids, and looped process liquids from the same fiberline of a hardwood kraft pulp mill. This allowed for a detailed characterization of wood extractives and their transformations throughout the production process. The analysis was conducted primarily using gas chromatography-mass spectrometry (GC-MS), resulting in the identification and tracking of more than 100 compounds. 
Some of the most abundant extractives in eucalyptus – particularly β-Sitosterol – were studied in detail due to their potential impact on paper quality and their role in pitch deposition. Our study revealed nine possible transformation products of β-Sitosterol, providing hypotheses for its chemical behavior under industrial conditions. We proposed possible reaction mechanisms for these transformations, forming the basis for further investigation of experimental approaches to mimic these chemical transformations in a controlled laboratory environment. 
Understanding wood extractive transformation pathways in the fiberline serves as a starting point for understanding formation mechanism of pitch deposits and possibly developing strategies to avoid quality problems associated with deposits.