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:
The drawbacks of conventional defrosting methods can be avoided thanks to the ability of radio frequency (RF) 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 due to 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.
Radio Frequency at 27,12 MHz.
Construction in AISI 304 & 316 stainless steel submitted to anticorrosion treatments (passivation, pickling) and shot-peening finish.
Protection level IP65: the external protection boxes of the RF generator are made of insulating sandwich-type panels with sheeting and bearing frame in AISI 304 stainless steel.
Wide conveyor belt (up to 180 cm) made of certified food-grade rigid polyethylene modules or solid-surface reinforced polyester, depending on the product to be processed.
Built-in conveyor belt & tunnel washing facilities and full internal access for cleaning through the multiple side panel doors.
PLC control system for multiple product recipes.
Production capacities can vary depending on the type of product to be defrosted and the final temperature required.
STALAM RF defrosting equipment is available in sizes from 3 kW to 85 kW (output RF power values). Multiple modules can be combined to increase the production capacity even at a later stage as production requirements increase with business growth.
RF Power (kWRF) |
Dimensions LxWxH (m) |
Belt Width (mm) |
Additional module length (m) |
Generator cooling system |
Installed power (kW) |
3 | 1.1×0.75×1.6 | Batch unit | Not available | air | 5 |
7 | 4.2×1.4×2.6 | 0.6 | Not available | air | 12 |
20 | 5.7×2.0x3.6 | 1.4 | Not available | air | 35 |
40 | 7.7×2.0x3.6 | 1.4 | Not available | air | 66 |
85 | 9.2×2.4×3.6 | 1.8 | 5 | water | 140 |
Production capacities depend upon the type of product to be defrosted and the final temperature required.
Examples of products defrosted in a 85 kW single-module machine:
Meat: frozen pork, 25 kg blocks, from -20°C to -5/-3°C
Production capacity: up to 2,500 kg/h
Fish: frozen squid, 12 kg blocks, from -18°C to -4/-2°C
Production capacity: up to 1,250 kg/h
Vegetables: frozen IQF carrots, 20 kg bags, from -18°C to -1/+1°C
Production capacity: up to 1,400 kg/h