We developed a novel taste sensor with Langmuir-Blodgett (LB) films for evaluating degradation degree of beer. We used three kinds of electrode for sensing. stearic acid (SA) and lanthanide (terbium) coordinating with stearic acid (Tb-SA), were employed as sensing membranes and LB films of SA and Tb-SA were formed on three kinds of electrode. We measured the sensor responses to several concentrations of trans-2-nonenal which is produced during the progress of a degradation causing from the oxidation of fatty acids by malt-derived enzyme. As a result, the sensors have a capability of detecting several concentrations of trans-2-nonenal.