The process, known as microwave volumetric heating (MVH), delivers microwave energy into the centre of food and beverages. Foods are passed through a chamber fitted with a tube bearing microwave sources or magnetrons at a spacing of one every 300mm. The amount of energy is controlled by adjusting the number of magnetrons and flow rate through the chamber.
The walls of the microwave-transparent pipe, made of non-stick Teflon, remain at the same temperature as the liquid or material being heated which avoids producing hot surfaces.
Douglas Armstrong, AMT managing director, told FoodManufacture.com: “Conventional heating systems focus on heating the surface of the food or beverage and rely on conduction and convection (to cook or pasteurise the product).
“But microwave volumetric heating uses a microwave transparent tube which delivers energy equally and evenly through the food and beverage.”
Highly-adaptable, the process can lend itself to a range of uses from pasteurising fruit juice, cooked sausage to making jam or soup. Other applications include: Vegetable purees, rice, honey, cider, haggis, pet food, haggis and rendering of waste.
Practical, economic and technical
Armstrong divides the benefits into three categories: Practical, economic and technical. Most of the practical and economic benefits arise from its operation at ambient temperature. In avoiding hot surfaces, processing does not cause food materials to stick to the equipment making it easier to wash than conventional systems and cutting down-time.
“Washing time can be measured in minutes compared with hours for a steam-jacketed heating vessel,” said Armstrong. Quicker cleaning means using less water and less energy leading to lower costs.
The equipment has a small factory footprint occupying a space 3m long, 2m high and 1m wide.
Further economic benefits stem from the efficiency of the cooking process. In some applications, such as pasteurising cooked meats, MVH can lead to energy savings of 90% compared with conventional cooking systems.
Cooking times of two to three hours in conventional ovens can be reduced to 20 seconds, said Armstrong. But he acknowledged that in some applications conventional plate heat exchangers still hold the advantage.
The AMT150 machine can produce 150 litres of pasteurised juice per hour, whereas the AMT1500 can produce 1500 litres per hour.
Turning to technical benefits, Armstrong said that MVH kills micro-organisms at lower-than-expected temperatures, preserves micro nutrients and can allow salt and fat reductions without compromising taste.
“We don’t know precisely why micro-organisms are killed so effectively but it may be to do with the microwave energy and pulsating electric fields.”
Rapid heating and cooling also preserves functional elements, such as anti-oxidants and vitamins, more effectively than conventional treatment systems, said Armstrong.
Flavour and colour also seem superior to conventionally-treated products. “Fruit juice pasteurised by MVH is virtually indistinguishable from fresh,” he added.
Salt reduction
The speed of the process also seems to give treated products a saltier taste than normal cooking which could offer the possibility of salt reduction. Salt reductions of between 30 to 50% may be possible benefiting the quality and shelf life of milk, juices, cooked meats and other products.
“We are looking at using it to help prepare ready meals because it could allow us to reduce their salt content.”
Also, some proteins subjected to the treatment appear to take on the mouth-feel of fat. So, it may be possible to reduce the fat content of foods and beverages.
The price of MVH system depends on application and ancillary equipment but could cost between £60,000 to £300,000.
The first commercial application of the technology will be installed in a UK food factory over the next month.
The process was developed through partnership between AMT and Queen Mary University, Belfast. It was facilitated by the agency Interface financed by the Scottish Funding Council and the Scottish government.