The wheat straw lignin-rich fraction (WSLig-RF) can be used as a raw material for the production of metabolites for industrial use if ligninolytic mitosporic fungi are used for its biodegradation into aromatics and short-chain fatty acids (SCFAs, i.e., SCFA2–6). Although methods for the production of SCFA2–6 have been described previously, quantitative data of SCFA2–6 production have not been reported. The objectives of this study were to investigate the biodegradation of different concentrations of WSLig-RF by Aspergillus fumigatus and to identify whether SCFA2–6 production was dependent on the concentration of aromatics. A. fumigatus generated 2805 mg L−1 acetic acid when mixed with WSLig-RF at a concentration of 20 g L−1. Thus, aromatics are a substrate for the biosynthesis of SCFA2–6, and their production depends on the concentration of WSLig-RF aromatics.