The aim of this process is to dry the product and to strengthen its aromas and / or to strengthen the structure of raw products.
Field of Application
Typical products that are roasted are: coffee, grain products and processed cereals, nuts, cocoa, chicory and fruit.
Techniques, methods and installation
The raw product is normally exposed to hot air (at temperatures over 100 ° C). Sometimes the raw product is pre-dried. The moisture content is thus reduced from 8-20% to less than 1%. When the product has reached a sufficient moisture content under high temperature (i.e., over 120 ° C), reactions take place in the product. These so-called Maillard reactions are important in the formation of aromas in coffee and cocoa. The duration of this roasting process depends on the product and the specific aromas required. Burning times for coffee vary from 1 to 20 minutes, while for cocoa and other products this can run up to 180 minutes. When the product temperature reaches the required level, the Maillard reactions are stopped by cooling the product with air or by cooling the product with water followed by air cooling. Roasting can be carried out both in batch and continuously. Typical installations for batch scheduling are: a drum burner, column burner (cocoa), rotating disc burner, fluidized bed burner, spray bed burner, etc. At each installation the product is simultaneously heated and moved. The product can come into direct contact with the hot air (convective heat transfer) or in contact with a heated surface (conductive heat transfer). Usually it is a combination of both. Cooling takes place in a separate installation. This can be a cooling screen through which air is passed or a spray bed cooler or any other installation where the raw product is in contact with fresh air. Cooling with water can take place in the combustion chamber and sometimes in the cooling installation. Cyclones are used as an integral part of the process of removing particulate matter (mainly consisting of product remains and peels) from the air before it is discharged into the atmosphere. The recovered material is then reprocessed. The cooling air is also emitted to the atmosphere.