Innovation: Secrets of ohm cooking: Heating with electric current offers alternative to freezing food

A DEVELOPMENT in food processing, which has won a Queen's Award for Technological Achievement, promises to provide such a competitive edge that most of the companies that have bought the system prefer not to reveal their names.

Ohmic heating is a method of sterilising food so that it can be stored, like canned food, at room temperature for up to two years, yet retain the taste and appearance of cook/chill foods, which have a shelf life of days and must be kept refrigerated. It has been now been commercialised by the food and drink processing company, APV.

To date the company has sold 18 ohmic heating units worldwide, including six in Japan. But only two purchasers of the new processing method - the Wildfruits Products Division of Nissei Company in Japan, and Sous Chef, now part of Heinz in the UK - are prepared to be named.

Paul Skudder, operations manager at APV, said: 'Ohmic heating will allow companies to introduce high quality variants of existing products. Our customers want their forward development plans to be confidential because the food market is highly competitive.'

Ohmic heating involves passing an electric current through the food, which then heats up like the bar on an electric fire. Most foods contain enough water with dissolved ionic salts to conduct electricity in this way. Every part of the food heats up at the same rate, so ohmically sterilised food is not overcooked.

In conventional sterilisation low-acid products must be heated to at least 121 degrees centigrade for at least three minutes at their slowest heating point - usuallly the centre of the largest particle. Overheating the liquid like this makes the outer particles of the food go soft and kills any vitamins.

The ohmic method works with any food that conducts electricity, can be pumped through the system and has food pieces of less than one inch square, such as soups, stews, sauces, pasta and curry dishes. It can also be used for processing fresh fruit for pie fillings or compotes. In the case of strawberries, the fruit remains whole and firm, quite unlike canned or defrosted fruit.

Ohmic heating cannot be used for the same range of ready meals as the cook/chill method, but it can produce food of the same quality. Although it costs more to preserve food by ohmic heating than by freezing, the subsequent costs are lower because goods do not need to be distributed and stored in freezers. It has advantages over canning both in the time taken to process the food and the quality of the product.

Ohmic heating was invented by the electricity companies' research arm, EA Technology, in Chester in the 1970s and licensed to APV in 1984. The first system was sold in 1988.

Sous Chef is the only company in the UK to have installed ohmic heating, though APV does have a plant in Wantage where food companies can run tests.

Heinz is tight-lipped about Sous Chef's ohmic developments, saying they are very much at the R&D stage. The company says it has done some consumer testing but will not name any products.

(Photograph omitted)