Capsule OEM Fill Routes Compared: Direct Powder Filling, Wet Granulation and Pellet Systems
A common assumption is that capsule manufacturing means putting powder into a shell, which is why the process route line on a quotation often gets little attention. In practice, the same prescription delivered by direct powder filling, wet granulation or coated pellets produces products that differ by an entire grade in fill accuracy, content uniformity, dissolution behaviour and appearance, at costs that can vary three to five fold. At the start of a capsule OEM programme, the route decision effectively sets every downstream choice: equipment, batch size, and how hard the registration dossier will be. Changing it later means repeating pilot runs and stability work from the beginning.
1. Direct powder filling: simplest, and the most demanding on the blend
Direct filling means milling, sieving, blending and filling. It is the shortest route, the cheapest, the kindest to heat-sensitive actives, and it needs no drying equipment. Its constraint is the physical character of the blend itself. Poor flow makes the dosing disc fill unevenly and pushes fill-weight variation out of specification. Low bulk density creates a volume problem: a size 0 capsule holds roughly 0.68 ml, so a blend at 0.35 g per ml tops out near 0.24 g. A formula needing a 0.5 g load then has to move to size 00 or even 000, and a 000 capsule is not something most consumers in this market will swallow comfortably. There are two ways out. Glidants such as colloidal silica or magnesium stearate improve flow, but dosing has to stay tight because excess slows disintegration. Granulation raises bulk density. Direct filling also places the entire burden of content uniformity on the blending step, which is why formulas with a high-potency component present at only a few milligrams per capsule almost always have to be granulated or pelleted instead.
2. Wet granulation: the default for most prescriptions
Wet granulation agglomerates powder with a wetting agent or binder solution, then dries and screens it. It solves three problems at once - flow, bulk density and content uniformity - which is why it is the default for most formulas. The cost is a wet and warm step that does not suit thermolabile or moisture-sensitive materials, and a process that grows from blend-and-fill into blend, granulate, dry, screen, final blend and fill, with the equipment and labour that implies. Three control points matter most. Binder quantity and addition rate set the particle size distribution, and adding too fast produces large lumps. Drying temperature and end-point moisture set granule hardness and downstream disintegration: too dry and the granules are hard and slow to break up, too wet and they cake or grow mould in storage. Screen mesh sets the fines fraction, and too many fines returns the process to the flow problem it was meant to solve. Binder choice deserves a decision as well - PVP K30 in water is broadly applicable but hygroscopic, HPMC is gentler on sensitive formulas, and starch paste is cheap but weaker and slower to granulate.
3. Pellets and coated pellets: built for modified release and combinations
The pellet route builds spherical particles of roughly 0.5 to 1.5 mm, optionally film-coats them, and fills them into shells. It delivers three things nothing else can. Incompatible actives can be pelletised separately and filled into the same capsule, which solves combination products. Coating delivers enteric protection, sustained release or taste masking, which powders and granules cannot do. And pellets disperse widely through the gastrointestinal tract, giving lower inter-subject variability and more consistent dissolution. The costs are equally clear: the longest process chain of the three, high equipment barriers - extruders, spheronisers or fluid-bed coaters, significant yield loss at every transfer, and a unit cost typically three to five times direct filling. It is therefore justified in three situations - a genuine modified-release or enteric requirement, a combination where ingredients must be physically separated, or a very low-dose active demanding exceptional uniformity. For a conventional supplement, pellets are usually over-engineering.
4. Five questions that decide the route
The route should not be chosen by habit. Work through five questions in order. First, what is the load per capsule and which shell size is targeted, which sets the bulk density requirement. Second, does the formula contain heat- or moisture-sensitive material, which cautions against wet granulation. Third, is there a low-dose high-potency component, which sets the level of uniformity demanded. Fourth, is enteric protection, sustained release or taste masking needed - if so, pellets are close to the only answer, although enteric shells themselves can be a compromise. Fifth, what are the target cost and first-order volume, which sets how many process steps the product can carry. Once those five are answered, the route is usually determined. There is also a middle path worth knowing: dry granulation by roller compaction adds no liquid and no oven, suits moisture-sensitive formulas and is shorter than wet granulation, at the cost of harder granules, slower disintegration and a requirement that the material actually compacts well.
5. What to fix once the route is agreed
Agreeing the route is the beginning, not the end. Three further points need settling before sampling. Equipment compatibility: filling machines meter differently - dosing disc, piston, vacuum - and each has its own expectations for particle size and flow, so the manufacturer should state an acceptable particle size distribution for their own machines. This matters especially when a brand switches contract manufacturers. Shell selection: gelatin, HPMC and enteric shells differ substantially in moisture requirements; gelatin shells need the fill kept at low moisture with tight room humidity control, while HPMC shells tolerate drier fills better but cost more. Pilot batch size: process verification needs at least three runs near production scale, because flow in a small laboratory blender is not the same as flow in a production hopper, and bridging or ratholing only shows up when material sits under real production rhythm. Writing these three into the agreement prevents a great deal of rework and argument later.
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Vitamin D3 K2 with Magnesium & Zinc Softgels | VITAMIN D3+K2 MAGNESIUM+ZINC Softgels OEM | Calcium + Magnesium + Zinc + Vitamin D3 Softgels | CALCIUM+MAGNESIUM+ZINC D3 Softgel OEM
About Guangzhou Mesen Health Biotechnology Co., Ltd
Guangzhou Mesen Health Biotechnology Co., Ltd is located in the Huashan Science and Technology Park, Huadu District, Guangzhou. The company has focused on OEM and ODM services for the big health industry for nearly 20 years, operating dedicated research, production, sales and management centres, and maintaining long-term strategic partnerships with well-known Chinese medicine colleges and research institutions. Capabilities span pressed candy, gummies, capsules, solid beverages, herbal teas, plant beverages, protein powders, dietary supplements and enzyme jelly - from formulation development through contract manufacturing. For details on minimum order quantities, sampling lead times and quotations, see our manufacturing advantages and product range, or contact us for a tailored proposal.
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