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Defrost
Rapid RF defrosting: how it works
Traditional defrosting
The choice, implementation and monitoring of freezing and defrosting methods are of paramount importance in the quality control of raw materials and processed food products. Traditional defrosting methods introduce a number of problems directly related to heat transfer phenomena:
Heat transfer is an intrinsically slow mechanism and, the larger the size of product, the longer the time required for the defrosting process; this causes a long delay between the removal of the product from the cold store and the next processing or utilisation stage;
Since bacteria can survive at negative storage temperatures, in the slow defrosting process there is considerable opportunity for bacteria growth in the product;
Proportionally high drip losses may result from lengthy defrosting times, causing changes in the product texture and leading to a significant economic loss;
It is not possible to speed up the defrosting process by increasing the temperature, as this may cause severe deterioration of the product surface;
Long defrosting time means a batch process is unavoidable, resulting in high handling costs with the additional risk of breakage, bruising and other product damage;
Since the heat required for defrosting is supplied by air, water or steam in processing rooms or equipment having large contact surfaces with the environment, the process speed is often influenced by the external ambient conditions, which are difficult to control.
The RF defrosting method
The drawbacks of conventional defrosting methods can be avoided thanks to the ability of Radio Frequency (RF) electromagnetic fields to rapidly generate heat volumetrically within the product. The heating process is fast, uniform and controlled, resulting in a significant reduction of drip losses and minimising product deterioration caused by bacterial growth. The RF heating method offers flexibility in the production scheduling and is the ideal solution for many tempering, softening and defrosting processes.
The product is placed on the machine’s conveyor belt and is transferred continuously through the RF unit (tunnel) passing between upper and lower metallic plates. These plates (also called electrodes) form an electrical capacitor and the product in between the plates becomes the dielectric element of that capacitor. The electrode plates are connected to a radio frequency generator oscillating at a frequency of several million cycles per second.
When the RF generator applies high frequency alternating voltage between the capacitor plates, the dipolar water molecules of the frozen product will vibrate and rotate attempting to align themselves according to the fast changing opposite plates polarities. This phenomenon causes intermolecular friction, which will in turn generate heat rapidly and uniformly within the whole product mass regardless of its size, weight, shape and thermal conductivity. The amount of heat generated inside the product and the defrosting time are accurately controlled through the voltage applied on the electrode plates and the speed of the conveyor belt.
Benefits
Defrosting in minutes
Defrosting is achieved in minutes rather than hours/days, even for large product blocks and, if necessary, directly inside packaging used for storage or retail distribution (carton boxes, polyethylene liners, etc.).
No dripping, no product degradation
The process speed and uniformity can minimize the risk of product degradation (blood loss, deterioration of sensory, chemical and physical properties, bacterial growth, etc.), thus helping to improve product quality.
Higher product yield
Defrosting can be achieved with virtually nil drip loss, that means eliminating completely the weight losses (up to 6-8%) caused by conventional defrosting methods. The improved yield brings immediate economic benefits that allow for an RF equipment pay-back period as short as 6 to 12 months.
Uniform and controlled treatment
The product can be obtained at the correct temperature needed for the next process. Also, weather and external ambient conditions do not affect the treatment, so that it can be controlled accurately and consistently.
Less floor space, reduced process cost
Radio frequency equipment requires much less floor space compared to the traditional, large defrosting rooms or equipment; defrosting costs are also reduced drastically, thanks to the absence of energy losses to the ambient.
In-line process
Thanks to the high process speed, radio frequency defrosting can be carried out continuously, with significant logistic advantages in product handling and production scheduling. The production can be organised according to "just-in-time" criteria - a great advantage in the case of sudden orders, last-minute changes in the order or under processing, etc.
Specific features of the RF defrosting equipment
RF operation frequency: 27.12 MHz
SUS 304 stainless steel structure after anti-corrosion (passivation, pickling) treatment and sand blasting.
Protection level: IP65. The external protective cover of the RF generator is made of insulating sandwich plate composed of SUS 304 stainless steel plate and support.
The wide conveyor belt (up to 180cm wide) is made of certified food grade rigid polyethylene modules or surface hardened reinforced polyester. Which one to choose depends on the product to be processed.
Built-in conveyor belt and channel cleaning device. The machine can be fully accessed through multiple side doors for cleaning.
The PLC control system can be used for the defrosting process formula of a variety of product.
Modular structure: the specification of Staram RF defrosting machine is 7kw/85kw/170kw. Multiple sections in series connection can be used to improve the output. If the output increases, additional RF modules can be easily used in series connection with the used defrosting equipment.
