Coca-Cola and PepsiCo are changing the way they make the caramel colouring used in their drinks as a result of a California law that mandates drinks containing a certain level of carcinogens bear a cancer warning label.

Consumers will notice no difference in our products and have no reason at all for any health concerns

The companies said the changes will be expanded across the US to streamline their manufacturing processes. The changes have already been made for drinks sold in California.

Coca-Cola and PepsiCo acc-ount for almost 90 per cent of the US soft drink market, according to industry tracker Beverage Digest.

The American Beverage Association, which represents the broader industry, said its member companies will continue to use caramel colouring in certain products but that adjustments were made to meet California’s new standard.

“Consumers will notice no difference in our products and have no reason at all for any health concerns,” the association said in a statement.

A representative for Coca-Cola, Diana Garza-Ciarlante, said the company directed its caramel suppliers to modify their manufacturing processes to reduce the levels of the chemical 4-methylimidazole, which can be formed during the cooking process and as a result may be found in trace amounts in many foods.

“While we believe that there is no public health risk that justifies any such change, we did ask our caramel suppliers to take this step so that our products would not be subject to the requirement of a scientifically unfounded warning,” Ms Garza-Giarlante said in an e-mail.