California has officially given its blessing to coffee, declaring the beverage does not pose a "significant" cancer risk despite containing a chemical listed by the state as being carcinogenic.

Key points: Roasting coffee produces acrylamide, which is listed by the State of California as carcinogenic

Roasting coffee produces acrylamide, which is listed by the State of California as carcinogenic California's Proposition 65 requires all products to be labelled if they contain chemicals which cause cancer or birth defects

California's Proposition 65 requires all products to be labelled if they contain chemicals which cause cancer or birth defects California's health department used a WHO review to declare there is inadequate evidence that coffee itself causes cancer

The official ruling, proposed a year ago and confirmed on Monday (local time), came in response to a Los Angeles judge ruling Starbucks and other companies failed to show that benefits from drinking coffee outweighed risks from a byproduct of the roasting process.

The judge's ruling put the industry in jeopardy of hefty civil penalties and in the position of either developing a process to remove the chemical, or warning consumers about the risk of cancer.

The chemical in question, acrylamide, is on a list that California says causes cancer, though other groups classify it as a "probable" carcinogen.

Under a law passed more than three decades ago by California voters — known as Proposition 65 or Prop 65 — products that contain chemicals which cause cancer or birth defects must warn consumers about those risks.

Other chemicals on California's list include well-known carcinogens such as alcohol, petrol, lead, diesel exhaust fumes, asbestos and nicotine but also some you might not suspect, including aloe vera leaf extract and wood dust.

A non-specific Prop 65 warning sign seen in 2014 at the picnic area next to the tram area at Disneyland Resort. ( Wikimedia Commons: Patrick Pelletier )

Signs did not initially have to list chemicals by name, resulting in potentially vague warnings in areas where people might encounter vehicle exhaust, including Disneyland. However, a ruling in August 2018 required warning signs to be more specific.

Acrylamide is a chemical "formed in certain plant-based foods during cooking or processing at high temperatures, such as frying, roasting, grilling, and baking," according to the California government.

Foods affected include potato chips and French fries, canned black olives, roasted nuts, toast — and roasted coffee beans.

The Californian government advises cooking toast and chips to the lightest colour acceptable in order to minimise exposure to acrylamide.

Coffee a 'complex mixture' of chemicals

The Office of Environmental Health Hazard Assessment, which implements Prop 65, concluded there was no significant risk after a World Health Organisation review of more than 1,000 studies found inadequate evidence that coffee causes cancer.

Further, it concluded coffee reduces the risk of some types of cancer.

"Coffee is a complex mixture of hundreds of chemicals that includes both carcinogens and anti-carcinogens," said agency spokesman Sam Delson.

"The overall effect of coffee consumption is not associated with any significant cancer risk."

It was the first time the state had declared such a brew of chemicals safe despite the presence of carcinogens, Mr Delson said.

The coffee industry cheered the ruling.

"This is a great day for science and coffee lovers," said William Murray, president and chief executive of the National Coffee Association USA.

"With this news, coffee drinkers around the world can wake up and enjoy the smell and taste of their coffee without hesitation."

The NCA had challenged the 2018 court ruling, releasing a statement saying: "The US Government's own dietary guidelines state that coffee can be part of a healthy lifestyle."

The Council for Education and Research on Toxics, which successfully sued the coffee industry in a case that has dragged on more than eight years in the Los Angeles Superior Court, will challenge the validity of the state's regulation in court, said attorney Raphael Metzger.

Mr Metzger, who represents the small non-profit in its lawsuit against Starbucks and about 90 coffee companies, said the regulation was adopted in violation of state law and disregards the statutes the agency is supposed to implement.

He said the regulation can not be applied retroactively to nullify the judge's ruling.

ABC/AP