Nutrient Gelatin is a differential medium used to determine whether microorganisms produce gelatinase, an enzyme capable of hydrolyzing gelatin proteins. Each tube contains approximately 8 mL of medium that solidifies into a deep format and is inoculated by a straight stab through the center. Unlike agar media, gelatin melts at incubation temperatures, so results are interpreted after refrigeration. Following incubation, tubes are cooled to approximately 4°C for 15–30 minutes. If the organism produces gelatinase, the gelatin is hydrolyzed and the medium remains liquid after cooling. If the enzyme is absent, the gelatin solidifies again. This reaction helps identify organisms with proteolytic activity and is commonly used in classical bacterial identification.