Rapid in-line tempering or partial thawing can process bulk frozen food products in minutes, not days, Food & Beverage Industry News reports.

Rapid in-line tempering technology continues to gain popularity globally and the Australian market is starting to catch up. This method uses Radio Frequency (RF) via a uniform, controlled process, which rapidly generates heat volumetrically within the product.

Equipment that utilises this superior defrosting method avoids many of the pitfalls of traditional defrosting and allows products to be processed with or without packaging.

Conventional tempering, or defrosting, typically sees pallets of frozen product stored in a controlled atmosphere staging room. Each day the temperature is gradually increased until the product is thawed.

Not only is this process slow, taking five to seven days, but temperature variation can occur between the cartons on the outside of the pallet versus cartons on the inside of pallet.

These rooms take up valuable floor space in the facility and require a refrigeration system to control the atmosphere and temperature. With this method, products are also double handled because they must be moved in and out of the defrosting room.

Heat and Control national sales executive, Glenn De Silva, said Stalam Radio Frequency equipment helps to avoid these issues, and more.

“This equipment doesn’t take up as much space as traditional tempering rooms and saves on valuable real estate,” he said.

“You avoid double handling, and the product is tempered within minutes, not days.

“This technology has been around for a while, almost as long as microwave, but it’s very different. The frequency is a lot lower and therefore more controllable.”

This is in comparison to microwave which, De Silva said, is far less controllable.

“If you could see the microwaves bouncing around in there, they are very random, uncontrolled and at a high rate,” he said.

“That’s why it’s common to get hot and cold spots when cooking with microwave.”

But the longer waves created with radio frequency means they can be more finely tuned and controlled.

“But because RF operates at a much lower frequency you make the full amount of power available and the product only draws what it requires for the process,” said De Silva.

Rapid In-line tempering equipment is placed at the start of a production line where it defrosts the frozen product prior to further processing and value adding.

Product can be defrosted on demand, in minutes. This improves cash flow for a business by removing the need to hold pallets of product for days on end and saving valuable floor space in the factory.

Rapid in-line tempering can defrost, and temper entire shift loads on-demand, allowing a processor to order bulk products to fill urgent, short delivery orders.

Also, with conventional defrosting, urgent, short delivery orders are impossible to fill as product must be ordered weeks in advance and cannot be defrosted in time.

Product is placed on the machine’s conveyor belt and then transferred through the RF unit (tunnel) passing between upper and lower metallic plates (electrodes).

When the RF generator applies high frequency alternating voltage between these plates, the dipolar water molecules of the frozen product vibrate and rotate in the attempt to align themselves according to the fast-changing opposite plates polarities.

This causes intermolecular friction, which in turn generates 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 to the electrodes, the distance between them and the speed of the conveyor belt.

Radio Frequency vs Microwave Frequency

The benefits of using RF in food processing are many and this technology can be easily explained when comparing it to Microwave (MW) Frequency.

Firstly, it uses a much lower frequency (27.12 MHz) than MW (915 MHz) and produces a much longer wavelength of 11m – compared with 0.32m for MW. It has a broad length of penetration into the frozen product – ranging from 500mm to 1000mm. This broad penetration of the radio wave is what allows frozen products to be defrosted and tempered evenly as heat is generated volumetrically.

RF penetrates inside any packaging used for storage or retail distribution including carton boxes, polyethylene liners, etc.

Meanwhile, Stalam RF units’ range in size from 7kW, 20kW, 40kW and 85kW (available in modules from 85kW) and will only draw the energy needed for a particular product.

“This translates to reduced operating costs,” said De Silva.

No Drip Loss or Product Degradation

Process speed and uniformity minimise risk of product degradation from drip loss, maintaining product quality.

“Reductions in drip loss translate to increased yields for the processor and greater profits.”

Because tempering achieves virtually no drip loss, the weight losses (up to 6-8 per cent) typically associated with conventional defrosting methods is eliminated.

For processors of bulk frozen products, plastic entrapment is a common problem. It happens when an attempt is made to remove the plastic liner (or bags) the product was frozen in, while it’s still frozen.

During freezing, plastic becomes easily caught in the crevices of the product, where it can remain trapped, and this poses a safety issue if not detected. RF technology eliminates the possibility of plastic entrapment, and some processors are using the technology for this purpose alone.

RF technology was first used by industrial bakeries to dry biscuits, crackers, and cereals after baking and for the pasteurisation and sterilisation of solid packaged food or viscous liquid products.

This technology has also been used for disinfestation and sanitisation of dry agricultural commodities such as grains, seeds, and pulses.

Today many processors use it to defrost cuts of beef, pork, beef kidney, tongue, and other organs, whole and cut poultry, whole fish, and fish chunks, fillets and fish portions.

Rapid in-line tempering equipment is also used by processors of bulk frozen fruits and vegetables.

With benefits such as significant time savings, no double handling, no damage to products and increased yields, the rapid in-line radio frequency defrosting method is gaining the attention of food processors.

“Processors lose thousands of dollars every shift through drip loss alone,” said De Silva.

“Savings on drip loss, time, labour, no-plastic entrapment and running cost benefits all contribute to a shorter return on investment (ROI).”