Copper surfaces 'kill kitchen bacteria'

Cooking pots and kitchen work surfaces made of copper rather than stainless steel or plastic could reduce the risk of food poisoning, scientists said yesterday.

Researchers have found that copper actively kills potentially harmful bacteria such as E. coli 0157 and could therefore be safer than other materials. Copper, which was recognised by the ancient Egyptians as a good metal for keeping drinking water pure, seems to produce chemically charged particles or "free radicals" that attack bacterial cells. Professor Bill Keevil of the University of Southampton said tests had shown copper could kill colonies of E. coli within hours, whereas the same bug could survive for months on stainless steel, the most common work surface in commercial kitchens.

"Stainless steel is used throughout the world because of its perceived hygienic properties. It always looks like a nice, clean and bright surface," Professor Keevil said. "But a closer look reveals scratches and marks which, on a microscopic scale, are more like valleys. It is very easy for harmful bacteria to get into these crevices and rubbing a cloth or brush across the surface may not be sufficient to get them out."

Research by Professor Keevil shows that at the chilled temperatures normally used to store food, bacterial survived for 35 days and sometimes for three months on stainless steel surfaces.

However, no microbes remained alive after 14 hours if the chilled surface was made of copper or, in the case of a brass, an alloy of copper and zinc, after 12 days. At room temperatures, the time taken for the bacteria to die was shortened to 34 days for stainless steel, four days for brass and four hours for copper.

Professor Keevil said a problem with using copper in the kitchen was that it could be attacked by acidic foods, such as lemon juice. "We're trying different copper alloys to see which one is best suited to the kitchen," he said.