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, the gummy releases cleanly. In practice that means two controls: starch conditioned to a target moisture and packing density, and a small amount of mineral oil or high-stability vegetable oil combined into the starch bed to keep the interface from bonding. 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.
Starch recovery after demolding
Separation does not end when the gummy leaves the cavity. Pieces carry residual starch on their surfaces, and the starch that absorbed moisture from the setting slurry is wet and no longer free-flowing. Both streams have to be handled. The trays are inverted, and the product passes through a screen or a gentle rotary tumble to knock off the surface starch. Pneumatic lines move the recovered starch to conditioning equipment that dries, sieves, and recompacts it before it is stamped into fresh cavities. The same oil treatment that limits bonding at the interface also cuts how much starch has to be recovered in the first place. Adhesion that runs too high shows up twice: once as dusting and defects on the piece, and again as a slower, dustier finishing line and a heavier reconditioning load on the starch system.
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.