Powder encapsulation

The material meets all the requirements on paper, and yet the batch is rejected? This is a well-known scenario in capsule production, especially when the key physicochemical parameters of the material have not been properly assessed. In powder encapsulation, it is precisely physicochemical parameters such as particle size, flowability, and moisture content that determine the success of the entire production process.

What does powder encapsulation involve? 

Powder encapsulation remains one of the most commonly used methods for manufacturing dietary supplements and many medicinal products. Although the process itself may appear simple and repeatable, in reality it is highly dependent on how the material behaves during capsule filling. Free-flowing powders are used almost exclusively in hard capsules, whose design (two-piece, allowing opening and closing) enables precise dosing of solid materials with a defined density and flow properties. Soft capsules, intended mainly for liquid and semi-liquid formulations, are not used for conventional powders. If a product is in the form of a dry fill material (powder, granules, pellets), hard capsules are the natural technological choice.

Stages of the encapsulation process 

The encapsulation process itself consists of several stages, such as: preparation and homogenization of the blend, powder dosing, capsule closing, and quality control. Among these, the dosing stage is critical, because this is when the properties of the powder directly affect the repeatability of the fill weight and the uniformity of the product. If the material does not behave consistently (e.g. it does not flow evenly or undergoes segregation), deviations in capsule weight and irregularities in content uniformity occur, which are difficult to correct at later stages. In practice, this means an increased number of rejects, production line downtime, and raw material losses.

Particle size and the encapsulation process 

The granulometric composition, i.e. the particle size distribution of the powder, largely determines how the material behaves during dosing and capsule filling. Parameters such as D10, D50, and D90 make it possible to assess powder uniformity – a material with uniform particle size ensures repeatable filling, whereas a broad distribution increases the risk of ingredient segregation and dose non-uniformity. Particle size also affects flow properties — particles that are too fine cause dusting, caking, and electrostatic charging, making dosing more difficult. Meanwhile, particles that are too coarse may lead to uneven capsule filling and difficulties in achieving the required dose. Optimal particle size is a compromise between good flowability and effective packing of the material.

Powder flowability and the production process 

An equally important parameter is powder flowability, which directly affects the smoothness of the production process. Flowability often determines whether the line operates consistently or whether downtime and dosing problems occur. It is assessed using indicators such as:

• Carr’s Index (the degree of powder compressibility based on the difference between bulk density and tapped density); 
• Hausner ratio (the ratio of tapped density to bulk density); 
• angle of repose (the angle of the cone formed by the powder). 

Good to know 

The flow properties of a powder may also be negatively affected by other factors and other physicochemical parameters, such as: 

• irregular particle shape, resulting in increased friction; 
• electrostatic charges – promoting adhesion to surfaces; 
• moisture content – leading to agglomeration and caking. 

In practice, it is most often the combination of these factors, rather than a single parameter, that is responsible for process-related problems. Read more to find out: Properties and composition of pharmaceutical raw materials. 

Material preparation 

Optimal material preparation begins with understanding the factors affecting its flowability. One of the most effective methods is granulation. Wet granulation (which involves combining particles using liquids and binders) improves powder uniformity and flowability, while dry granulation (based on mechanical compaction) works well for moisture-sensitive materials. Technological excipients, such as lubricants or anti-caking agents, support powder stability and flowability, while appropriate storage conditions protect the material’s properties from moisture, high temperature, and light.

Quality control and the most common causes of rejects 

Quality control in powder encapsulation requires continuous monitoring of parameters at every stage of manufacturing (from powder mixing and dosing to closing and packaging) and systematic documentation of results. The most common causes of batch rejection – blend non-uniformity, deviations in capsule weight, and problems with the flowability or moisture content of the material – often result from insufficient material control at an early stage. To minimize the risk of rejects and ensure product repeatability, a preventive approach is necessary, including thorough material characterization, formulation optimization, and continuous real-time monitoring of fill weight, filling uniformity, and deviations. We should also not forget about documenting material and process parameters, which is essential for compliance with GMP and customer expectations. Documentation should include: material specifications, quality test results, and records of manufacturing parameters. In this way, the customer gains confidence in the quality of the product, while the manufacturer can maintain high standards and full batch traceability. Well-maintained documentation is also important during audits and inspections, serving as evidence that all regulatory requirements have been met. Find out what the principles of Good Manufacturing Practice (GMP) mean in practice.

Powder encapsulation – what determines success? 

In summary, it is the properties of the material that largely determine the stability and repeatability of the encapsulation process. Conscious management of powder parameters, such as particle size, flowability, moisture content, and compatibility with the capsule, is a prerequisite for achieving high production quality and efficiency.

In the case of complex formulations, repeatability issues, or planned production scale-up, it is worth considering cooperation with an experienced contract partner. This solution makes it possible to shorten implementation time and significantly reduce the risk of errors. At Eubioco, we combine modern technological facilities with an expert approach to product development, from formulation to commercial production. With us, you can bring your product to market faster, while also gaining confidence in quality, safety, and full control over the process. Check out our guide, Contract Manufacturing of Supplements Step by Step, and see how efficiently an idea can be turned into a ready-made product with a competitive profile, tailored to market needs.

BIBLIOGRAPHY 

1. European Medicines Agency (2024). Guidance on Good Manufacturing Practice and Good Distribution practice: Questions and Answers [online]. Available at: https://www.ema.europa.eu/en/human-regulatory-overview/research-development/compliance-research-development/good-manufacturing-practice/guidance-good-manufacturing-practice-good-distribution-practice-questions-answers [accessed online: 19.03.2026]
2. Finke, J.H., Kwade, A. (2021). Powder Processing in Pharmaceutical Applications—In-Depth Understanding and Modelling. Pharmaceutics, 13, 2, 128. https://doi.org/10.3390/pharmaceutics13020128.
3. Shanmugam, S. (2017). Granulation Techniques and technologies: Recent Progresses. BioImpacts, 5, 1, 55-63. https://doi.org/10.15171/bi.2015.04.
4. U.S. Food & Drug Administration (2022). Questions and Answers on Current Good Manufacturing Practice Regulations | Production and Process Controls [online] Available at: https://www.fda.gov/drugs/guidances-drugs/questions-and-answers-current-good-manufacturing-practice-regulations-production-and-process [accessed online: 19.03.2026]Vadaga, A.K., Gudla, S.S., Nareboina, G.S.K., Gubbala, H., Golla, B. (2024). Comprehensive review on modern techniques of granulation in pharmaceutical solid dosage forms. Intelligent Pharmacy 2, 5, 609-629. https://doi.org/10.1016/j.ipha.2024.05.006.