Campden BRI scientist Dr Craig Leadley told Foodmanufacture.co.uk: “Ohmic heating never really took off in the 1980s, but we’re now seeing a resurgence of interest because of its ability to deliver improved product quality.”
During ohmic heating, food serves as an electrical resistor, and is rapidly heated by passing an electrical current through it. The electrical energy is dissipated into heat, which results in rapid and uniform heating and eliminates burning, fouling on heat transfer surfaces and overcooking.
The technology was particularly well-suited for heating liquid foods containing large particulates, such as soups, stews, and fruit pieces in syrup, in which quality was often compromised by conventional cooking where heat was transmitted to the food by conduction and/or convection. This often caused overheating of the liquid in order to make sure the solids were properly sterilised, said Leadley.
By contrast, ohmic heating volumetrically heated the entire mass of the food, so that the temperature of the particulates was raised at the same speed as the surrounding liquid, creating a higher quality product, and far shorter cooking times, he claimed.
“I am aware of several industrial applications in the food industry and two in the UK and Norway using equipment supplied by APV, while [Italian supplier] Emmepiemme now has something like 30 applications worldwide on everything from baby food to fruit purée. It’s actually much more commercially advanced than many people realise.”
Firms wanting to test the technology on their products could conduct trials at Campden BRI, which has a 5-litre batch ohmic heating system available for use, said Leadley.
Other potential applications for ohmic heating include treating fruit juices to inactivate proteins; blanching; thawing; starch gelatinisation; speeding up fermentation in dairy production and fruit peeling without chemicals.
However, foods high in fat can present challenges as fat globules are poor conductors due to lack of water and salt.
Ohmic heating is also being trialled by UK firm C-Tech Innovation in partnership with anaerobic digestion company Bioplex to pre-treat sludge and slurry waste containing animal by-products, enabling their safe disposal. (Animal byproducts legislation requires such waste be heated to a minimum of 133°C for 20 minutes at 3-bar pressure.)
C-Tech is also designing ohmic heating systems to treat compost leachate, a liquid that drains out of compost, which must be pasteurised to destroy pathogens, said the firm.