Film formation on a moving pin
Shells are formed by dipping heated pins into gelatin solution and withdrawing them, so the film must set at a predictable rate and to an even thickness. Viscosity governs pick-up and drainage directly. A grade that varies in viscosity between batches produces walls that vary in thickness, and wall thickness drives both machine performance and dissolution.
Moisture is the property to guard
A finished shell holds a narrow band of moisture. Too dry and it becomes brittle, splitting during filling or in the blister; too moist and it softens, deforms and can stick. Control depends on the drying environment as much as on the gelatin, and shells are hygroscopic in storage exactly as the raw material is.
Dissolution has to be reproducible
Capsules are expected to release contents within a defined window, and that behaviour must hold across the product's shelf life. Cross-linking, driven by aldehydes from excipients or packaging and accelerated by heat and humidity, can slow dissolution over time. Screening for cross-linking risk during development is far cheaper than discovering it in stability.
Clarity and colour are quality signals
Transparent and lightly coloured shells expose any haze or off-colour in the gelatin. For these formats the optical specification is as binding as the mechanical one. Where colourants are used, batch-to-batch colour consistency of the base gelatin determines how tightly the final shade can be held.
Microbiological limits are non-negotiable
Pharmaceutical use brings defined microbiological criteria that must be met on every batch and evidenced in documentation. This is a routine expectation of the supply arrangement rather than an occasional check, and the associated records form part of the material's release.
Qualify against the machine, not the datasheet
Capsule machines differ, and a grade that runs well on one may not on another. Qualification should be done on the equipment that will run it, at production speed, with the intended fill. A grade approved on paper and never trialled at speed tends to reveal its limitations during the first large campaign.
Capsule machines differ, and a grade that runs well on one may not on another. Qualification should be done on the equipment that will run it, at production speed, with the intended fill. A grade approved on paper and never trialled at speed tends to reveal its limitations during the first large campaign.
