Tequila vinasses are organic wastes generated during ethanol fermentation at elevated temperatures (≥90 °C) and pH ≤ 4.0, making them hazardous to the environment. This paper describes a new, simplified UV–vis spectroscopy-based procedure for monitoring the adsorption of color compounds in tequila vinasses onto silica-based adsorbents, along with an optimized synthesis method to produce the most efficient sol–gel synthesized thiol-functionalized adsorbent. Under optimized conditions, the uptake capacity of this adsorbent reaches 0.8 g g−1 in 90 min. Experimental results demonstrate that the adsorbent has a specific affinity for melanoidin-type molecules. The adsorbent demonstrates excellent thermal stability (~316 °C). The results of this work indicate that the adsorbent possesses potential in the treatment of tequila vinasses from wastewater discharges.