The purpose of melting is to be a phase change from solid to liquid, to organize the material for further processing (e.g., for fats, processed cheese) or to recover the molten fraction (i.e., in fat recovery).
Field of Application
The main applications of melting in the food industry are in chocolate molding, the production of processed cheese, the processing of oils and fats and the recovery of animal fat from meat residues.
Techniques, methods and equipment
Proccessing kettles are used for melting. These can be operated either batch-wise or continuously. Heating may be carried out by direct steam injection or indirectly by steam jackets. Processing kettles are available in various sizes and shapes. In continuous processing, scraped surface heat exchangers are applied. Som typical examples of melting processes are described below:
a) Melting in the production of processed cheese
Milled cheese and other ingredients are put into a processing kettle and heated to a temperatur normally not less than 75°C to ensure a complete pasteurisation of the processed cheese. Agitation durig processing is important for a complete emulsification of the processed cheese. The temperatur and duration of the process depends on the type of processed cheese aimed for and the nature of the raw cheese.
b) Melting to recover fat from meat residues
To recover fat from meat residues two process methods are used: wet melting or dry melting. In the wet melting process, the raw material is heated in the process kettle by direct steam injection to a temperature of about 90°C. This results in a watery phase and a fat containing phase. The phases are separated by decantation and centrifugation.
In the dry melting process, the raw material is indirectly heated in the processing kettle (a kettle with a steam jacket). All the water which evaporates is removed from the kettle (under vacuum). The liquid phase (molten fat) and dry phase (fat free meat residue) are separated by decantation.