The continuous phase of the suspension of swollen-in-water modified waxy maize starch was analysed. The composition, concentration and molecular weight of the substance released from modified starch granules were determined. Starch granules were swollen in excess water at 73 °C and held at this temperature for 1 min. Centrifugation was used to separate the granules from the supernatant; the latter was then submitted to physico-chemical analysis. Surface tension measurements showed that the supernatant was different from pure water indicating the presence of dissolved polymeric material(s). Differential Scanning Calorimetry and iodine staining results revealed the presence of amylopectin. Analytical Ultracentrifugation and Size Exclusion Chromatography coupled with a Multi-angle Laser Light Scattering were used to determine the sedimentation coefficient and weight-average molecular weight of the soluble amylopectin fraction as well as giving an indication of solution concentration. The molecular weight of dissolved amylopectin was around 1.5 × 106 g/mol and its concentration in the supernatant varied from 0.6 to 6.7 mg/mL for initial 10 mg/mL and 50 mg/mL starch suspensions, respectively. The sedimentation coefficient, weight-average molecular weight and amylopectin concentration in the supernatant all increased non-linearly with the initial starch concentration in the suspension.