Chocolate dragee coating is a specialized process in which fruits, nuts, and various confectionery items are coated with chocolate or compound chocolate. In most cases, properly combining the components of the process leads to significant increases in production capacity while simultaneously reducing energy costs.
General Information About Dragee Chocolate Coating
When selecting products to be coated, care should be taken to choose products with good rolling properties and high fracture resistance (or flexibility). The humidity control equipment to be integrated into the system aims to stabilize the temperature and humidity of the air to be sent over the products. In this way, system design criteria should be determined with the goal of achieving the increased production output of winter months in summer and spring as well, independent of seasonal air effects. Particularly due to rising absolute humidity levels in summer months, wet air being delivered to the dragee coating pans causes: extended coating times, spotting on the surface of coated products, and products sticking to each other.
Therefore, in the chocolate coating process, the coating procedure consists of 3 main stages, and different air conditions are required at each stage.
Pre-Coating:
Especially with products such as nuts, crystallization (whitening) can be observed on coated surfaces over time as nut oil mixes with the chocolate due to friction in the rotating dragee drums. This causes the chocolate to have a matte and brittle structure. It also softens the chocolate layer, preventing the chocolate from adhering properly to the dragee content. As a result, an uneven and rough coating occurs. If a thick chocolate layer is planned, the pre-coating step may not be included in the process. Manufacturers can prepare the product for the chocolate coating stage by fixing the dragee with "coating powder" consisting of cocoa and sugar powder before coating.
Chocolate Coating:
The type of chocolate to be used (dark, milk, white), its melting temperature, fluidity, and homogeneous application can change the coating duration. A rotating drum system is used to ensure even coating. This drum continuously moves the dragees, ensuring that the chocolate and syrups are evenly distributed on the surface. The flow rate, temperature, and relative humidity value of the air to be sent to the dragee drums play a critical role here. Otherwise, the coating process may be prolonged and product deterioration may occur.
Dragee Polishing:
Polishing is one of the most important stages of the dragee production process. In this stage where polishing agents (shellac or gum arabic) are used intensively, the first layer of products is coated with syrup in rotating drums. During this process, the air sent into the drum should dry each layer quickly, preparing the product surface for the next agent. The drying process should continue until the stickiness on the product surface is removed. For better surface gloss, the polishing process continues with polishing agents such as shellac.
Determining Humidity Control Levels and Tolerances
In the dragee coating process, custom designs specific to the process stand out in achieving the correct humidity control level. In parallel with the general flow of production, controlling the humidity and temperature of the air sent to the rotating dragee drums and clarifying tolerances according to the product additive amounts is essential. Removing the heat generated by friction in the dragee drums through cold air sent into the drums and keeping the chocolate cold hardens the chocolate surface and makes it resistant to surface depressions that may occur during rotation. Sending air at 10-12°C temperature and 40-50% relative humidity levels at an appropriate flow rate accelerates drying, coating, and polishing processes. Air that is drier or at a higher flow rate than necessary causes cracking and depressions on the product surface due to rapid drying.
Main Outlines of Ventilation System Design and Humidity Load Distribution
Some of the parameters to consider in the process during the design of air conditions to be sent into the dragee pans are as follows:
- Number of dragee pans,
- Hourly production capacity of dragee pans,
- Name of the process (coating, polishing),
- HVAC details of the environment where the pans are located, if any,
- Location of the dragee pans and position of the equipment that will send air into the pans,
- Dust conditions of the dragee room,
- If a return line is to be used, whether it will be taken from inside the pans or through central diffusers on the ceiling (if taken from inside the pans, only the moisture from the product will be calculated in the return line; if taken from the room, the moisture gain will be calculated as product + room).
Especially in coating applications containing dust, comprehensive filtration of return air is not preferred due to high filter investments and increased maintenance costs. In the polishing process, the correct design approach is to include a certain amount of fresh air into the system air, creating two separate design conditions for summer and winter seasons.
When designing, the relationship between the dew point (dp) of the air condition to be sent to the dragee pans and the outdoor dry bulb temperature should be checked on an annualized basis at the location where the facility is installed. The system should be optimized for energy efficiency through automation infrastructure using the controlled weather data.
Based on the referenced design principles, it is assumed that in the chocolate coating system operating as an open system, the thermal and moisture loads will come entirely from the outside air and be reduced to final conditions. In this case, the system will be designed with two main loads: sensible heat load from fresh air, and latent heat in the fresh air (which will be converted to sensible heat by the humidity control device).
The heat generated by the rotating products in the dragee pans is removed by sending air at 10-12°C at an appropriate flow rate (different temperature values are referenced for different additives and product types). Therefore, in summer design conditions, the sensible heat load from the outdoor environment is the difference between the average maximum dry bulb temperatures in the relevant region and the air condition to be blown into the dragee pans. Additionally, the latent heat in the outdoor air will be converted to sensible heat by the humidity control device in proportion to the amount of moisture removed, and will be added to the system as sensible heat. The more moisture is removed, the higher the dry bulb temperature of the air at the process output of the humidity control device will be.
For this reason, before the humidity control equipment selected for the process is included in the system, the total sensible heat load and total latent heat load should be calculated, and the "latent heat" load should be balanced between the silica gel rotor humidity control device and the cooling system in a way that optimizes the initial investment and operating cost of the humidity control device.
At this point, the unit cost of the thermal energy source to be used for the reactivation heater of the humidity control device will determine the decision. If the cost of steam or natural gas to be used for the reactivation heater is more economical than electricity cost, the latent heat (moisture) can be removed more cost-effectively by the humidity control device. However, high-rate discharge of latent heat by the silica gel rotor humidity control equipment will provide high dry bulb temperature air input to the system, resulting in high initial investment costs for the humidity control device. This ratio can be balanced by sustainably low operating costs. If no alternative energy source is used in the humidity control device, then as much moisture as possible should be removed through cooling, and then air should be sent to the humidity control device.
From a thermodynamic perspective, reaching -2°C dew point levels for air at 10°C and 40% relative humidity conditions is not sustainable or efficient through cooling alone. Therefore, the use of a silica gel rotor humidity control device in the system is inevitable.
System Control and Positioning
In dragee coating and polishing processes, in the design of the air conditioning unit suitable for the temperature and humidity conditions requested by the manufacturer, cooling/heating of the air, control of the reactivation energy of the silica gel rotor humidity control device, and sending air at the correct pressure and flow rate to the pans are extremely important. Due to the sequential arrangement of dragee pans, equal flow passing through the first and last pan demonstrates the importance of the external static pressure values of the fans selected in the system and the duct cross-section diameters.
If return air is to be taken from the system, the humidity-controlled air conditioning unit should be positioned as close as possible to the process, and care should be taken regarding the sealing of the negative pressure (vacuum) effect of the return line. System control in the polishing process can be designed as fresh air and return air, with conditioning done by taking return from the indoor environment. In this case, using a dew point sensor integrated into the system provides convenience for damper automation. To prevent the coil from freezing in winter conditions (when design conditions require it), a certain proportion of monoethylene glycol should be added to the fluid circulating in the system.
In conclusion, the chocolate dragee coating and polishing process is a complex procedure consisting of multiple stages that must be specially designed with proper engineering infrastructure. Careful temperature and humidity control at each stage is one of the main factors that determines the quality of the final product. With proper humidity control, you can achieve delicious, shiny, and long-lasting chocolate dragees.