Electrochemical Characterization of Iso‐ α ‐Acids Using a Graphite Sheet Electrode: An Alternative for Bitterness Determination in Beers

Hops ( Humulus lupulus ) are one of the main raw materials used in beer production, responsible for striking sensory characteristics such as aroma and, especially, bitter taste. During wort boiling, thermal isomerization of α ‐acid molecules occurs, producing iso‐ α ‐acids, compounds directly related to bitterness intensity. In this context, this work proposes an electrochemical method for beer bitterness determination based on iso‐ α ‐acid quantification. First, α ‐acids were isolated from Sabro hop variety, isomerized to obtain iso‐ α ‐acids, and characterized by ¹³ C nuclear magnetic resonance spectroscopy. Subsequently, a complete electrochemical characterization of iso‐ α ‐acids was performed using a three‐electrode system, containing a graphite sheet (GS) as the working electrode. Cyclic voltammetry measurements of iso‐ α ‐acids revealed an oxidation process at +1.1 V (vs. Ag|AgCl|KCl _(sat.) ), which was considered for electroanalytical purposes. An analytical curve was obtained in the concentration range from 0.1 to 4.0 mg L ⁻¹ using square‐wave voltammetry, selected due to its higher sensitivity. Following extraction using acidified isooctane and pretreatment with anhydrous magnesium sulfate, beer samples were analyzed to obtain bitterness values based on iso‐ α ‐acids quantification, and the results agreed with the values reported by the manufacturers. The proposed electrochemical method circumvents the lack of selectivity of the spectrophotometric method since some co‐extracted interfering species also absorb at 275 nm, the maximum absorbance wavelength of iso‐ α ‐acids. Hence, we demonstrate that electrochemical methods using GS electrodes hold promise for future applications in beer quality control.