Reverse osmosis (RO) is a common unit operation in the coffee industry, used for nonthermal membrane concentration in instant coffee powder and coffee concentrate production. RO of coffee is affected by fouling that is often irreversible and limits processing time and the membrane’s life. Fouling mechanisms are complex and are mostly dependent on feed chemistry, and membrane surface characteristics that influence foulant-membrane interactions. Coffee is a complex beverage encompassing over 1000 different volatile organic compounds, polysaccharides, organic acids, lipids, and minerals, making it difficult to predict and mitigate the membranes fouling mechanisms. The objective of this work is to assess membrane fouling during concentration of coffee by RO, with a focus on membrane-product interactions. Reconstituted coffee from instant coffee powder was RO concentrated using a bench top MMS RO system equipped with RO polyamide thin film composite membranes. The membranes were characterized and assessed for their performance before concentration, after concentration, and after cleaning. Signs of irreversible fouling were observed after only a single coffee concentration run. The membrane’s surface properties indicated fouling through electrostatic attraction between hydrophilic, positively, or neutrally charged compounds and the hydrophilic, negatively charged membrane. FT-IR and XPS data suggested fouling by organic compounds, especially sulfur-containing compounds. This was corroborated with surface morphology imaging where the absence of large deposits indicated that fouling was caused by small molecular weight compounds. Understanding the mechanism of initial stages of fouling will help determine how further fouling may develop and identify appropriate mitigation strategies to minimize or prevent fouling.