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How are hard gelatin capsule shells manufactured?
Beyond Biopharma · Pharmaceutical Gelatin FAQ
Hard gelatin capsule shells are made on fully automatic machines that form, dry and assemble two halves. Clean, precisely tapered stainless-steel pins are dipped into a warm, temperature-controlled gelatin solution so that a thin, uniform film coats the lower part of each pin; as the pins rotate and move through long drying tunnels, the film dries and sets into a firm shell. The dried shells are then slipped off or stripped from the pins, trimmed to the correct length, and finally the longer cap half and shorter body half are brought together into a matched, ready-to-fill capsule. Throughout, the gelatin is kept at the right viscosity and temperature, and humidity is tightly controlled, because film thickness and drying set the shell's strength, weight and dissolution behaviour.
Preparing the gelatin dope
Production begins well before any shell is formed. Pharmaceutical gelatin, purified to pharmacopoeia grade and certified as to source, is dissolved in hot water together with plasticiser (to stop the film becoming brittle) and processing aids, then usually colourant and any opacifier such as titanium dioxide are added according to the batch recipe. The clear, bubble-free "dope" is held as a warm liquid at a controlled temperature and viscosity; its exact solids content and temperature govern how thick a film each dip produces, so they are measured and adjusted bath by bath.
The dipping step
Inside the machine, banks of stainless-steel pins are mounted on frames, or "bars". Each pin is precisely shaped and polished to the internal profile of one capsule half — the longer cap shape for one set and the shorter body shape for another. In the dipping cycle:
- The frame of pins is slowly lowered so that only the lower end of each pin enters the warm gelatin bath.
- A thin, curved film of gelatin coats the submerged portion of the pin.
- Because of surface tension and pin geometry, the film is thinnest at the rim and a little thicker at the rounded tip, forming the natural closure shape of a capsule half.
Drying, stripping and trimming
Dipping alone does not make a shell — controlled drying sets the strength. The film-coated pins move through long, carefully climatised drying tunnels where air temperature and humidity are precisely controlled so each half dries evenly without warping or becoming brittle:
| Stage | What happens |
|---|---|
| Rotating & drying | Pins slowly rotate to dry the film all round as they travel through conditioned air |
| Stripping | The dried, firm shell halves are slipped off / stripped from the pins with mechanical jaws and rollers |
| Trimming (cutting) | The open rim of each half is trimmed to obtain the exact required length and a clean, flat closure edge |
| Joining | A cap half and a body half are aligned and locked together to form a complete, ready-for-filling capsule |
Why humidity quietly decides shell quality
Gelatin's moisture content sits at a critical balance. Too dry and shells crack; too moist and they stick, deform or soften. Modern capsule plants therefore invest as much in environmental control as in the mechanical line: the drying tunnels and the room operate in a narrow range of temperature and relative humidity, because water loss during drying defines shell weight and strength, and the moisture a finished shell picks up over time shapes its elasticity and dissolution. Precisely because final moisture content is so consequential, buyers expect a certificate of analysis recording moisture and dissolution-related properties for every batch.
Quality control on the line and off it
Shell manufacture is continuous and self-checking. In-line gauges monitor shell length, wall-thickness profile, weight and closure quality, rejecting shells that drift out of tolerance. Off-line, representative samples are tested for the pharmacopoeia parameters that matter for capsules — disintegration or dissolution behaviour, moisture, physical dimensions, appearance and microbiological cleanliness. Only shells that pass are packed and stored under controlled conditions ready for the capsule filler.
Summary for buyers
- Dipping, drying, stripping, trimming and joining are the universal core steps of hard-shell manufacture.
- Film thickness and drying regime, set by the gelatin dope and the machine's climate, drive shell strength, weight uniformity and dissolution.
- Buy from suppliers who control humidity and provide batch documentation, since shell quality is decided on the line, not in the lab.
- Specific machine configurations vary between manufacturers; the supplier's process description and specifications are the authoritative references.
