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What moisture and particle-size specs suit capsule production?
Beyond Biopharma | Pharmaceutical Gelatin FAQ
Short answer: For capsule production, pharmaceutical gelatin is commonly supplied at about 10-13 % moisture as a typical working range, with a controlled particle-size distribution, so it dissolves evenly, dispenses consistently and behaves predictably on dipping and filling equipment. Moisture, particle size and storage humidity interact, so the right target depends on your line, the season and the specification agreed with the supplier.
Why moisture content matters
Gelatin is hygroscopic: it picks up and gives off water with the surrounding air. The moisture content of the delivered powder therefore affects almost everything downstream. If the powder is too damp it can cake, weigh inconsistently and support microbial growth in storage; if it is too dry it can become static, dust more and hydrate unevenly. Capsule makers typically work with gelatin in the region of 10-13 % moisture as a reference range, because at that level the powder flows and dissolves dependably without giving moisture a chance to cause trouble.
Moisture on the certificate of analysis
On the COA, moisture is usually reported as loss on drying under defined conditions, with a method taken from the current compendium or the supplier quality system. Check that the value sits inside the range you agreed, and note the method, because different drying conditions give slightly different numbers. Moisture is not a fixed property of the grade alone: the same lot will drift a little with warehouse humidity, which is why the packaging, the storage room and the time between opening and use all matter as much as the certificate.
Why particle size matters
Gelatin for capsule lines is almost always delivered as a powder with a controlled particle-size distribution rather than as random fragments. Particle size controls how fast the powder hydrates in warm water, how it behaves in dosing and conveying equipment, and how much dust and foam the process generates. A fine powder dissolves quickly because of its larger surface area but can dust, foam or float on the water surface; a coarser, more uniform granulation disperses with less dust but needs more time or agitation to dissolve. The right profile is the one that gives your dissolving tank a consistent, complete solution in your cycle time.
Reference values at a glance
| Property | Typical reference for capsule lines | What it affects |
|---|---|---|
| Moisture (loss on drying) | About 10-13 % | Hydration behaviour, caking, flow, bioburden during storage |
| Particle-size distribution | Controlled sieve profile set by supplier grade | Dissolution speed, dust and foam, dosing consistency |
The table gives typical reference values, not a universal specification. Confirm the agreed range and the sieve profile on the certificate of analysis for the exact grade you buy.
How to confirm a grade for your line
Before locking a specification, run the powder through your own process at your normal temperature, time and agitation, and watch for undissolved particles, foam, dust and weighing drift. Ask the supplier for the moisture range and the full sieve analysis, and store the gelatin in sealed bags in a cool, dry room so the certificate values still hold when you open the container. If your site is very humid or very dry, discuss a moisture target or storage plan with the supplier rather than simply accepting a generic range.
Related reading
See also how to read a pharmaceutical gelatin specification (COA) and what microbial limits apply to pharmaceutical gelatin.
