Dragee coating is a critical manufacturing process in the pharmaceutical and food industries, in which tablets, cores, or granules are coated with layers of sugar, chocolate, polymer film, or wax-based protective materials to improve the product's appearance, taste, stability, and controlled-release properties. The quality of this process depends heavily on the temperature and humidity conditions within the coating environment. When the relative humidity of the air fed into the coating pan is not controlled, the drying of the coating suspension is delayed, inter-layer adhesion deteriorates, and serious quality defects appear in the finished product. For this reason, the use of an industrial dehumidifier in dragee coating pans is indispensable for process repeatability and product quality.
In the dragee coating process, coating suspension is sprayed onto cores rotating inside the pan while dry air is simultaneously fed into the pan to ensure rapid and uniform drying of each layer. The relative humidity of the supply air must typically be maintained in the 5–15% range, a level that conventional HVAC systems alone cannot achieve. A dehumidifier integrated into the air handling line reduces the dew point of fresh or recirculated air to the target value and keeps the moisture content of the air entering the pan constant. This ensures that every coating layer forms under identical drying conditions, delivering consistent inter-layer homogeneity.
Humidity control is particularly critical in chocolate dragee coating. Chocolate is tempered at 30–32°C to stabilize its crystal structure; at this temperature range, ambient relative humidity above 40% causes surface sweating, dulling, and fat bloom on the chocolate surface. When a dehumidifier maintains the coating room's relative humidity at a steady 30–35%, the gloss, hardness, and crisp texture of the chocolate coating are secured. In sugar dragee coating, both the temperature and the moisture content of the air fed into the pan must be precisely controlled for each sugar layer to crystallize and harden properly; otherwise, layers remain soft, stick together, or develop irregular surfaces.
In pharmaceutical dragee coating, the importance of humidity control becomes even more pronounced. The thickness uniformity of film or sugar coatings applied to drug tablets directly affects the dissolution rate and consequently the bioavailability of the medication. Fluctuations in ambient humidity during coating cause some tablets to receive thicker or thinner coatings than others, increasing intra-batch variation. For GMP-compliant production, a stable, low relative humidity environment maintained by a dehumidifier in the coating room guarantees that every tablet achieves the same coating thickness.
Silica gel rotor dehumidifiers are the preferred technology for dragee coating applications. These units can reliably achieve very low relative humidity values of 5% and below, performance that exceeds the physical limits of compressor-based condensation systems. Rotor technology delivers air at a constant dew point to the coating line even during summer months when outdoor humidity peaks, ensuring the process can be sustained independently of seasonal conditions. Additionally, the low pressure drop characteristic of rotor technology facilitates easy integration with existing ventilation systems.
Correct sizing of the dehumidifier capacity for the coating process is decisive for both process efficiency and energy costs. The pan volume, coating type, suspension application rate, supply air flow rate, and target dew point are evaluated together to calculate the total moisture load. An undersized dehumidifier extends coating cycle times and reduces production capacity, while an oversized system wastes energy unnecessarily. A system dimensioned with accurate engineering calculations shortens coating cycle times, increases daily production capacity, and optimizes energy costs.
At NKT – Humidity Control Technologies, our expert engineering team designs industrial dehumidifier solutions tailored to your dragee coating pans, ensuring maximum coating quality, cycle time efficiency, and energy performance across chocolate, sugar, and pharmaceutical coating processes. For more information, please contact us through the form below.
