Porang (Amorphophallus muelleri Blume) tuber has a glucomannan content of 65.44 % (dry basis). Natural deep eutectic solvent (NADES) can isolate glucomannan from porang flour (NPF). Excess water in NADES causes NPF to form a gel, inhibiting glucomannan isolation. This study investigated the maximum hydration of betaine-glycerol-based NADES for isolating glucomannan. In addition, the central composite design was employed to optimize the glucomannan isolation using hydrated NADES through responses of yield, solvent recovery, glucomannan and ash contents, and viscosity of porang glucomannan flour (PGF). The glucomannan isolation variables were the liquid-to-solid (L/S) ratio, time, and temperature. The results showed that the maximum hydration of NADES for isolating glucomannan was 70 % (Wwater/Wtotal). The optimal conditions of glucomannan isolation were an L/S ratio of 20, an isolation time of 4 h, and a temperature of 32 °C, resulting in a PGF yield of 82.82 %, glucomannan content of 90.28 %, viscosity of 12.55 Pas, and molecular weight (Mw) of 1.29 × 106 g/mol. Temperature was the main variable affecting glucomannan isolation. Reducing the isolation temperature decreased the yield but increased the glucomannan content and viscosity of PGF. Increasing the isolation temperature to 60 °C enlarged the glucomannan granules by 50 μm and reduced their birefringence. © 2025