Nutrient Gelatin, often sold simply as Gelatin Medium, is described by multiple manufacturers as a medium for the detection of gelatin liquefaction by proteolytic microorganisms. Published sheets also note that gelatin liquefaction is an important test in the differentiation of enteric bacilli and that the medium may be used in some water microbiology plate count procedures. :contentReference[oaicite:4]{index=4}

The principle is simple: organisms that produce extracellular gelatinase hydrolyse gelatin into smaller soluble fragments. Because gelatin normally forms a semisolid gel when cooled, hydrolysis is observed as persistent liquefaction after incubation and cooling. ASM’s teaching protocol describes gelatin as serving both as a nutrient substrate and as the solidifying matrix in the test. :contentReference[oaicite:5]{index=5}

Published directions commonly specify suspending about 128 g in 1 L of warm water and heating to fully dissolve. :contentReference[oaicite:18]{index=18}

Dispense into tubes and sterilise by autoclaving. After sterilisation, the medium is usually allowed to cool upright so the semisolid gel forms correctly. :contentReference[oaicite:19]{index=19}

For interpretation, chill before reading to distinguish true gelatin hydrolysis from simple thermal melting. :contentReference[oaicite:20]{index=20}