Sol–gel processes were used to fabricate amperometric biosensors that are active for hypoxanthine (Hx) determination. Xanthine oxidase was immobilized in the bulk of the silica–graphite matrix (SGM) to produce electrodes where new surfaces can be generated on demand by mechanical polishing. The immobilized enzyme electrodes can be used in unmediated hydrogen peroxide oxidation mode, or in unmediated and mediated oxygen reduction mode, to result in three different types of Hx biosensors with detection limits of 1.3 × 10^–6, 5.6 × 10^–6 and 3.8 × 10^–7M, respectively. Benzyl viologen was used as the charge transfer mediator to enhance the response in the hydrogen peroxide production mode. The sensors show good linear response over a wide range of concentrations of about 1 × 10^–6–1 × 10^–3M. The use of bulk immobilization and the possibility of renewable surfaces have enabled the easy operation of these sensors with high stability. The experimental results from a carp sample stored under different conditions demonstrate the practicality of these sensors as simple, rapid and cost effective measurement of fish meat freshness.