The most effective way to make a starch mold unusable for a second cycle is to let the molding starch dry out completely. Starch holds a clean cavity because a small amount of residual moisture lets the grains pack against the impression wall. Remove that moisture and the starch turns dusty. The cavity edges crumble when the tray is handled, and the impression loses definition before the pieces are demolded. The lesson is that ideal molding starch stays damp but not wet.
Moisture moves into the starch during a run. Warm gummy mass is deposited into each cavity, and as the pieces set the starch pulls water out of them, so the starch that leaves the cycle holds more water than the starch that went in. After demolding, the starch is screened, dried, and cooled back to its working range before fresh impressions are pressed. Over-dry it in that conditioning step, or leave trays sitting exposed in a dry room, and the starch falls below the moisture level where it can pack into defined cavities.
Too little water leaves the starch dusty and unable to hold detail. Too much water makes it cling to the pieces, so product sticks and impressions slump. Gummies and jellies are commonly molded in starch at around 5% to 7% moisture by weight. Starch is not hard tooling. The medium is reused. Every impression is formed fresh, and its quality depends on the moisture the starch carried into that cycle. Controlling that moisture through the conditioning step is what keeps starch reliable as a molding medium.