Carefully controlled thawing and tempering

by Thomas Jensen
Bowl of mussels

Micro- and radio frequency waves offer advantages over traditional thawing methods

This article was featured in Eurofish Magazine 5 2022.

Based in Lyon, France, Sairem produces machines that generate radio frequency energy or microwaves for a variety of food related applications.

Heating fresh foods such as aquatic products, which have a high water content, with radio frequency (RF) is a way of extending the shelf life of the product without using chemical treatments. This removes the risk of any chemical residue in the product while achieving a later best before date. RF offers the advantages of rapid heating, deep thermal penetration, low cost and better quality control. RF heating can be used to cook, reduce microorganism counts, thaw, blanch, or disinfest food items.

Rapid and uniform heating

RF energy is produced in an RF generator which converts electricity into radio frequency waves. This energy is used to heat products and RF generators are therefore mainly used for thermal processes. When used in food processing, an RF generator enables food items to be quickly tempered or defrosted. Both RF and microwave frequencies are heating and drying technologies that work in more or less the same way: heat is generated when an electromagnetic field passes though the product. This electromagnetic field causes the molecules inside the material to vibrate which generates heat. Both technologies differ from conventional heating methods in that they warm the product uniformly throughout its volume. Other heating methods heat the product from the outside in by conduction. The main difference between RF and microwave technologies is the wavelength of the radiation that is produced. This has a bearing on how the energy travels and gets transmitted to the product.

Differences between the technologies can be exploited for different purposes

With RF generators the energy travels from one electrode to the other passing through the product and warming it. These generators are suited for warming products with a regular shape. The wavelength of the electromagnetic radiation they create at around 10 m is longer than that of microwaves. The radiation penetrates deeper into the product making them ideal for thick items. Since they warm the product more slowly than microwaves, they can be used for more delicate products. Microwaves, on the other hand, are created by a microwave generator and have a wavelength of 10-30 cm. They are particularly effective at treating products at high speed, especially those which have an irregular shape. The speed and uniformity at which they heat makes them ideal to quickly heat or dry food stuffs and to pasteurise liquids. Both technologies, radio frequencies and microwaves, improve thermal processing in the food industry as they can heat rapidly, uniformly, and preserve taste, colour, nutritional profile, and quality of the product without the use of any additives. Moreover, they can be combined with traditional heating techniques to give a comprehensive thermal treatment.

Precise temperature control is a major advantage when thawing

Sairem has worked with industrial solutions using microwaves and radio frequency technologies since 1978, when the company was established. It has a strong focus on research and development and has patented many of the technologies and processes it has developed. Most of the components are designed in-house, whether mechanical, electronic, or software which contributes to the quality and reliability of the equipment it sells. For food processors the company provides food safety and process efficiency with its MW and RF generators by shortening thermal processing times and reducing the growth window for bacteria and other pathogens. The technologies are reliable and very safe as the machines are closed and fitted with sensors in the case of MW generators, and interlocks in the case of RF generators to prevent any leakage of radiation. They are approved for use in the processing of organic products. In addition to shorter processing times these technologies heat from the inside out, eliminate cold spots, and enable precise temperature control. The ability to precisely choose the time and temperature of the process also ensures that bacterial growth is limited, thus contributing to the safety of the final product. Over and above this, the technology is energy efficient and based entirely on electrical energy, so there are no greenhouse gas emissions at the production plant.

Yields from raw material improve as does final product quality

Using RF or MW technologies to temper or defrost raw materials is not only quicker than traditional methods but also lessens drip loss and thereby improves the yield from the raw material. The homogenous temperature of raw material that is subjected to RF or MW is also better for subsequent processing operations which become more efficient and result in a better final product. The heat treatment can be arranged so that the material is treated continuously or in batches depending on the requirements of the processing operations. For fish processing operations Sairem offers both an RF and a MW solution depending on the customer’s requirements. The machines are rated to deliver power varying from 5 to 300 kW.
Sairem’s new generation of pasteurisation tunnels are suitable for all types of ready meals or for individual components. Depending on the ingredients and the customer’s process, the tunnel can either pasteurise only, or cook and pasteurise at the same time. The latter is more suitable for fish and seafood as cooking times need to be short. The more sensitive the ingredient, the better MW technology is suited to it. The tunnel pasteurises at a maximum temperature of 95-100°C depending on the product. It processes all types of trays no matter the size or the composition – plastic, glass or paper based. It can also be used for thermoformed packs and pouches.

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