High performance and reliable operation over three shifts, simple to clean and maintain, key features. Conveyor belts are at the heart of a successful process.
The cooling tunnel is the final step before packaging in the production of chocolate and moulded chocolates, biscuits, and baked goods. It is a delicate process. For products like chocolate and moulded chocolates, cooling must be precision controlled in order to obtain the crystallization that starts in the tempering machine. A correct cooling ensures that the products achieve an optimum gloss, are resistant to fat bloom, maintain snap, flavour and a pleasant taste – in other words maintain the integrity of the raw materials used during the various processing steps (mixing of ingredients, conching, tempering, and moulding). The cooling method depends on the products to be treated and is based on size, density and fragility of the products or the type of chocolate or cream. In general, confectionary products enrobed with low density coating are radiantly cooled initially in order to protect the thin and fragile surfaces. Products that need hardening and then cooling of the base are conduction cooled by a stainless steel bottom tray that is cooled by water under the belt. Finally, high density products, for example biscuits or baked goods, are cooled by convection with modulated temperature and airflows.
There is a wide range of cooling tunnels on the market that are designed specifically for the various cooling requirements of the product and for particular client needs. Belt tunnels are for cooling products like baked goods deposited directly on the belt itself, and for the enrobing line there are tunnels with plastic or metal net conveyors for moulded chocolates, bars, hollow products. The total utilizable length and width of the belt varies according to the application requirements. Products in moulds can also be cooled in vertical tunnels that achieve an optimum processing result with low space requirements. Bar type tunnels are ideal for small to medium artisan production. In chocolate production, tunnels must guarantee cooling without humidity. The cooling systems are chosen according to the specific characteristics of the line: radiant, convection and conduction, air flow with or counter to the movement of the product. To achieve the best result, tunnels can be divided into several cooling zones, each with its own air ventilation with independently regulated temperatures. Cooling is achieved through ventilation circuits with high yield evaporating accumulators (direct expansion), electro fans, semi-sealed moto-compressors, centrifugal or helicoidal fans. Modern tunnel have probes to measure the temperature, digital control instruments to measure the temperature while the speed of the belt is varied with an invertor. Many electrical control boxes are equipped with an operator panel for verification and set-up of the control parameters of the machine, graphics interface and memory to save the values of all the variables that are involved in the cooling phase.
What is required from a cooling tunnel
High performance and flexibility. These are the main cooling tunnel characteristics required by the confectionary industry. Producers are now designing modular solutions that combine a variety of sizes, characteristics and cooling elements to adapt to any application from filled chocolates to crèmes, biscuits and products with variable cooling requirements. Cooling is achieved through radiant, convection or conduction methods. Airflow, insulation and cover design must guarantee maximum thermal efficiency all along the length of the belt with precise temperature control. Cleaning and maintenance, energy efficiency and safety are also important. Most tunnels are modular to accommodate modifications and upgrades. They can be used stand-alone or in fully automatic or semi-automatic production lines. Many models offer insulated panels that can be taken off for fast and easy cleaning. CIP washing can be used on part or on the entire area. Tunnels equipped with CIP recycle systems use less water and detergent. The infeed height can be regulated so that movement is continuous with other feeding systems like the enrober, oven, etc. In some models, the optical sensor on the infeed and conveyor makes sure that the belt is perfectly aligned over the entire length of the cooling tunnel. With regard to cooling sections, many models offer stainless steel trays that are easily controlled for radiant and convection cooling, like a stainless steel bottom tray that can be water cooled for a rapid forced conduction cooling of baked goods. For more control over cooling, trays can be divided in the different sections. For work areas with area constraints, there are space efficient linear tunnels with a cooling area of just a few metres. It is possible to reduce the airflow humidity to zero with a series of deflectors that create a closed circuit of air. Even in the smallest tunnels, electronic temperature and humidity control is available, as well automatic thermostat and belt speed regulation. There are multi-function tunnels also on the market. In one direction, they function as enrobing lines for pralines, cakes, grissini, snacks and other baked goods. In the opposite direction, on a secondary level of handling of the product inside the chamber, the tunnel allows for cooling.
Conveyor belts: an integral part of the process
Conveyor belts are an integral part of the cooling process and are a key to success. Modern belts are resistant to hot water, detergents and disinfectants, allowing for various washing cycles without running the risk of delaminating or destruction of the surface of the belt. Most belts are made with materials that prevent the formation and spread of bacteria. Some producers utilize blue belts, a colour that is not present in food, making it easy to identify physical contaminants. These belts are also equipped with optical sorters. Belt edges can be sealed to prevent the penetration of oils, fats, water and bacteria and at the same time increase the service life of the belt by reducing the risk of product contamination. A critical feature for the success of a cooled product is the ability to be released, that is, ensuring that the products do not stick to the belt during the process and that the removal of product residue is easy. The belts with good release properties are those with a structured or anti-adhesive surface that ensure optimum release of sticky products which are typical in the confectionary industry. Belts with good thermal conductivity help with cooling chocolate that is hot off the production line. Belts that are completely inside the tunnel also have several advantages such as a cleaner environment, more protection from ambient condensation and humidity, and energy savings because the belt maintains a constant temperature during the cycle therefore eliminating the reheating step.