In starch-molded gummy production, demolding is a physical tug-of-war between three key forces: adhesion, cohesion, and viscosity. Each plays a distinct role in whether a gummy releases cleanly from the starch mold or tears, sticks, or carries excess starch with it.
Adhesion: the interfacial force
Adhesion is the attractive force between unlike materials - in this case, the gummy surface and the starch particles or conditioned mold surface. During starch molding, starch absorbs moisture from the deposited gummy slurry, which can create a bond at the interface. If adhesion is too high, starch clings to the gummy, causing rough surfaces, heavy dusting, or visible defects. If adhesion is low, the gummy separates cleanly.
Cohesion: the gummy’s internal strength
Cohesion is the internal strength of the gummy itself - the molecular forces holding the gummy matrix together. During separation, the gummy must withstand tensile and peel stresses without tearing or splitting. If the adhesive pull to the starch is stronger than the gummy’s internal cohesion, the gummy may break apart or leave residue behind in the mold.
Viscosity: the flow and deformation variable
Although viscosity is not an intermolecular force in the same sense as adhesion and cohesion, it is a critical bulk property during molding and release. At depositing, lower viscosity helps the slurry flow into starch cavities, but excessively low viscosity can cause deep starch penetration, effectively increasing adhesion after setting. At demolding, the gummy behaves as a viscoelastic solid, but its deformation rate and peel behavior are still influenced by its viscous character.
Which is most critical?
Adhesion is the most critical governing force for separation itself. Demolding is fundamentally an interfacial release event. If the adhesive interaction between the gummy surface and the starch mold is properly managed - through starch conditioning, moisture control, and surface release - the gummy releases cleanly. Cohesion and viscosity are essential supporting factors because they determine whether the gummy survives the release without tearing and how it responds to demolding stress. But the primary variable that decides clean separation versus sticking is the adhesive force at the gummy-starch interface.
At KorNutra, production teams monitor this balance by controlling starch moisture content and mold release conditions, keeping adhesion low while preserving enough cohesion for clean, intact demolding.