The process for making the colour of Coke and Pepsi is being altered in response to accusations that one of the ingredients is a known carcinogen.

Coca-Cola made the change even though it rejects the accusation made by the U.S. Center for Science in the Public Interest that the ingredient – compound 4-methylimidazole, also known as 4-MI or 4-MEI – poses a danger to consumers who drink cola.

“The fact is that the body of science about 4-MEI in foods or beverages does not support the erroneous allegations that CSPI would like the public to believe,” Diana Garza Ciarlante, a Coca-Cola spokesperson, told National Public Radio in the U.S.

Ciarlante said caramel coloring in Coke products has always been safe.

“Outside of California, no regulatory agency concerned with protecting the public's health has stated that 4-MI is a human carcinogen,” she said.

Pepsi is also changing its process while maintaining the colouring process is safe.

“The safety of our products is a primary concern at PepsiCo. Our beverages, and the ingredients that go into them, are and always will be safe for consumption,” Pepsi said in a statement. “This includes the caramel coloring that we use in some of our products. When California chose to add 4-MEI to its Prop 65 list, we asked our caramel suppliers to modify their manufacturing processes, which they have done. Over time they will expand this process for the rest of the country.”

Pepsi said customers will not notice a difference and cautioned them not to be concerned.

“There is no scientific evidence that 4-MEI in foods and beverages is a threat to human health. The FDA and other regulatory agencies, including the European Food Safety Authority and Health Canada, consider caramel coloring safe for use in foods and beverages.”

CSPI filed a regulatory petition against the artificial caramel colouring used in colas and other foods, in February 2011.

The artificial brown coloring is made using sugars with ammonia and sulfites under high pressure and temperatures, which results in the chemicals being produced, according to the CSPI.

“Carcinogenic colourings have no place in the food supply, especially considering that their only function is a cosmetic one. The FDA should act quickly to revoke its approval or caramel colorings made with ammonia,” said CSPI executive director Michael Jacobson.

Under California’s Proposition 65, food or products containing more than certain levels of cancer-causing chemicals must carry warning labels. California added 4-MI to the list in 2011.

To avoid being saddled with a cancer warning on every can and bottle, Coca-Cola required its supplier to change the way it manufactures the colouring, reducing the level of 4-MI.

The changes are being made to the product in California for now, but will be rolled out nationally in time, said Coca-Cola’s Canadian spokesperson, David Moran. He added that it’s premature to say what the timeline will be.

The changes will not affect the colour or taste of Coke, Moran said.

“Over the years, we have updated our manufacturing processes from time to time, but never altered our Secret Formula.”

Both the American and Canadian Beverage associations rejected the CSPI claims, pointing out that the U.S. Food and Drug Administration, the European Food Safety Authority and Health Canada consider caramel coloring safe for use in foods and beverages.

“Health Canada’s current determination is that low levels of 4-methylimidazole that can be found in food, including certain caramel colours, do not represent a risk to Canadians,” according to Barbara Lee, director of the bureau of chemical safety at Health Canada.