Continuous, rather than batch, heating of liquids and semisolids

Microwave volumetric heating could deliver cost benefits, slash energy consumption and increase efficiency in the food processing industry.

Advanced Microwave Technologies Ltd (AMT) and a team of experts from Edinburgh’s Queen Margaret University have been working together to establish the commercial potential of AMT’s system of using microwaves to heat liquids, suspensions and semisolids on a continuous basis.

Douglas Armstrong, AMT’s Managing Director, explained: “Commercial processing of many foods has changed little over the years and is traditionally carried out in batches in pots and ovens or by continuously using inefficient steam systems. Processing by these methods is highly energy inefficient, labour intensive and the systems require extensive cleaning. More importantly, cooking by these methods can cause considerable damage to the nutrient content, flavour and colour of the food, eg, processing fruit juice can reduce the nutrients and result in an inferior taste.”

The AMT system works by delivering microwave energy directly and evenly into any material being pumped continuously through a microwave transparent pipe. This new method of gently delivering energy, known as ‘microwave volumetric heating’, has many practical advantages. It eliminates hot surfaces, therefore preventing thicker foods such as eggs, sauces and jams from sticking. It is more controllable and is claimed to improve energy efficiency, allowing cooking costs to be reduced by at least half.

Traditional batch processes can be transformed into continuous ones - ultimately saving labour costs and downtime, eg, when machines are being cleaned. The technology is extremely versatile and the same equipment can be used across a range of food and drink products, from pasteurising fruit juice to producing cooked sausage.

Armstrong explained: “Whilst we were aware of many of the advantages of our technology, we needed additional technical and commercial experts to help us evaluate the potential benefits of the system within the food and drink industry. We found out about Queen Margaret University from Interface and we chose to work with the university because of its expertise in nutrition, its strong links with the food industry and its high-tech facilities.

“Together, we have carried out a series of feasibility trials within a newly developed test facility now at Queen Margaret University. We have now used the microwave technology across a range of products including fruit juice, root vegetables, cooked sausage, jam, custard and scrambled eggs. We’re even working on toothpaste!”

Dr Mary Warnock, Commercialisation and Knowledge Exchange expert, said: “So far, we’ve only scratched the surface. Our trials have highlighted the enormous potential of this versatile machine. We firmly believe that this technology can offer substantial benefits to the global food processing industry. The extent of its applications has yet to be fully realised.”

Dr Sue Gordon, the Food and Drink Business Development Manager at Queen Margaret University (sponsored by Scottish Enterprise), said: “In this difficult economic climate, it is critical that commercial organisations, particularly SMEs, realise that they can gain significant benefits from working in partnership with university experts.”

Following these initial trials, Queen Margaret University is so convinced by the technology that it has now created a trial facility to enable external companies to come and evaluate the system for their own applications.

Dr Gordon confirmed: “Already, there has been substantial interest from the food industry including the national food retailers, many of which have started using the trial facility as well as QMU’s growing expertise in this new technology.”

Dr Gordon concluded: “Queen Margaret University is establishing itself as the global centre for excellence in the use of this technology. We are already collaborating with a number of research partners to explore other practical and technical benefits within other areas of the food and drinks industry. For instance, we believe that the system could have a major role in reducing microorganisms during food production.”

The university welcomes enquiries from organisations that may be interested in any aspect of this work or seeing demonstrations of the machine.

The microwave volumetric liquid heating system

The AMT system allows practically any material that can be pumped through a 50 mm pipe to be heated and conditioned using microwave energy on a continuous basis.

The heart of the system is a wave-guide which allows magnetrons of varying power outputs (0.5 to 6 kW) to focus their energy uniformly in a narrow zone across the entire cross-sectional area of a microwave transparent tube (up to a diameter of 50 mm).

As the liquid passes through this zone, it absorbs microwave energy depending on its ability to absorb microwaves (calculated by its dielectric constant).

The amount of energy delivered is therefore almost infinitely variable and is dependent on the dielectric constant of the liquid, the power of the magnetrons, the speed of flow of the liquid and the number of magnetrons.

In addition, the distances between the magnetrons can be varied to allow different conditions to be achieved along the length of the system or treatment chamber.

The pressures and temperatures which can be achieved are only limited by the physical properties of the microwave transparent materials that are used to contain the liquid.

By adding the AMT mixing system, very thick difficult liquids can be handled or the pipe diameter increased. This is an infinitely variable system which allows the microwave treatment of liquids to be used on an industrial scale.

There are many advantages in being able to use the AMT system of microwave treatment to heat and condition liquids, suspensions and semisolids.

• There are no hot metal surfaces for difficult materials to stick to.
• Energy is distributed immediately and evenly throughout the total volume of the liquid.
• There are no boundary layer effects.
• Energy can be introduced in varying amounts and immediately stopped, making the process highly controllable.
• It is very efficient; up to 90% of the energy used is absorbed.
• The equipment has a very small footprint reducing building costs.
• Ancillary equipment like boilers and steam pipelines can be eliminated.
• Maintenance costs are very low.
• Microorganisms are killed at lower thermal retention times due to the rapid and even heating.
• Certain chemical reactions are accelerated due to the rapid heating and the direct effect of the microwaves.
• Yields of certain chemical reactions are significantly increased.

Potential applications for the microwave technology

Vegetable purees

The AMT System introduces a completely new way of manufacturing mashed vegetables and purees. Low-starch vegetables such as turnips and carrots can be minced and, with a minimum amount of water, may be pumped through the machine. After cooking at 85°C, the mash may be pureed and fed directly into existing filling or packaging lines. There is significant potential to produce an improved product with better retention of colour, flavour and micronutrients, and an increased shelf life.

Rice

The conventional, batch process of cooking rice is labour intensive and uses relatively inefficient methods of heating. AMT is working with Wright Flow Technologies Ltd to deliver a cost-effective solution using pump technology.

Soups

The AMT System allow soups and broths to be manufactured in a continuous process. Raw ingredients may be premixed and pumped directly into the system. Modern pump technology ensures that the particulate matter maintains its integrity, and the integral mixing device ensures the even heating of all the ingredients. The gentle cooking process allows the preservation of nutrients and flavours.

Honey

Food with a high sugar content, such as honey, may be thermally processed or pasteurised with ease. Because the AMT System contains no hot surfaces, the problem of ‘taints’ associated with other methods of pasteurisation is avoided. The gentle method of microwave heating also preserves flavours, micronutrients and colour. The AMT System may be fully integrated with aseptic filling equipment.

Pet food

The AMT System introduces a completely new way of manufacturing pet food. Offal, meat, stock and other ingredients may be premixed and pumped through the machine. After cooking the mixture may be fed directly into existing filling or packaging lines. There is significant potential to produce an improved product with better retention of colour, flavour and micronutrients.

Haggis

Thick mixes such as haggis may be successfully cooked using the AMT System. The unique integral mixing device ensures rapid and even cooking. The AMT System may be fully integrated with aseptic filling equipment.

Rendering of waste

The AMT System introduces a new way of rendering food waste. Offal and other waste from the meat or fishing industries may be chopped up, mixed with a minimal amount of water and pumped through the machine. Valuable side-products such as oils may be collected. The AMT System may also be used to sterilise waste, allowing fluid to be safely discharged to the sewer and solid waste to landfill.

Ciders and high-sugar drinks

Drink with a high sugar content, such as cider, may be thermally processed or pasteurised with ease. Because the AMT System contains no hot surfaces, the problem of ‘taints’ associated with other methods of pasteurisation is avoided. The gentle method of microwave heating also preserves flavours, micronutrients and colour.

Advanced Microwave Technologies

www.advancedmicrowavetechnologies.com

info@advancedmicrowavetechnologies.com