When coffee beans are first picked and removed from the fruit they're inside, they're a pale color.
It's only after they're roasted — cooked — that they take on a dark or light brown shade and develop that wonderful aroma that we associate with comfort and feeling alert.
But that cooking process creates byproducts. One of the chemicals formed when coffee is roasted is known as acrylamide, a substance that was was first discovered by Swedish scientists in 2002.
The chemical acrylamide is considered "probably carcinogenic" by the International Agency for Research on Cancer, and California considers it a substance that's "known to cause cancer." But whether there's enough of it in coffee to be concerned about is a different question.
Because of the presence of that chemical, the Council for Education and Research on Toxics filed a lawsuit in the state of California against businesses like Starbucks that sell coffee, asking that they be required to post warnings stating that coffee contains cancer-causing chemicals.
On March 29, a California judge ruled in favor of the lawsuit, so Starbucks and other companies will need to post warning signs (Starbucks had already agreed to post some warnings but they may need to become more prominent now). Whether they'll have to pay financial penalties has not yet been decided.
But that said, there's extensive scientific research on coffee, and most of it indicates that if anything, coffee consumption is associated with a lower risk for several types of cancer.
When it comes to acrylamide, the dose makes the poison
Pump enough of any chemical into an animal or person and you'll eventually get to a point where that substance is dangerous.
But these situations aren't always reflective of the real world.
In the case of acrylamide, we know that being exposed to too much of it is dangerous.
Data suggests that in large quantities, acrylamide is carcinogenic to some animals. Animal studies have shown that putting acrylamide in drinking water can give rats and mice cancer. But the doses they consumed in those studies are 1,000-100,000 times the amount people get through their diet.
Industrial accidents when people have inhaled large quantities of acrylamide have shown that it can harm humans. too. It's also one of the many chemicals produced in cigarette smoke, though in higher amounts than from coffee-making.
So far, there's no evidence that the amount of acrylamide in coffee is dangerous. Plus, it can't be avoided.
Acrylamide naturally forms when plants and grains are cooked at high temperatures. It's created in a process known as the maillard reaction, in which high heat transforms sugars and amino acids in ways that change flavor and tend to brown food. When potatoes, bread, biscuits, or coffee are heated, acrylamide forms.
It's present in about one-third of the calories the average US or European person consumes.
Humans also metabolize the chemical differently than animals do, and so far, studies haven't found any harmful connection between consumption of foods containing acrylamide and various common cancers.
A toxic situation
Previous lawsuits by the Council for Education and Research on Toxics have led potato-chip makers to say they'd cut acrylamide levels in their products — they also paid a hefty fine. (According to the Associated Press, the law that lets groups sue companies for exposing people to chemicals has helped eliminate some dangerous chemicals but has also been "widely criticized for abuses by lawyers shaking down businesses for quick settlements.")
But changing the coffee-roasting process isn't really an option, and that process is always going to create byproducts like acrylamide.
There's still no good reason to believe drinking coffee is dangerous. Caffeine, which is also found in coffee, can be deadly at high doses — but that doesn't mean all caffeine is bad.
The International Agency for Research on Cancer removed coffee from its "possible carcinogen" list in 2016.
At least one major review of studies found that the more coffee people drink, the lower their risk for liver cirrhosis or liver cancer. A review of more than 200 studies found that people who drank three or four cups of coffee per day were 19% less likely to die from cardiovascular disease. Heavy coffee drinkers have an 18% reduced risk for cancer overall, according to one large study, and some data indicates that coffee drinkers may be less likely to suffer from oral or pharyngeal cancer and advanced prostate cancer.
There are other potential health benefits to coffee, too.
While it's not a good idea to inhale acrylamide from an industrial site, there is no reason to think the amount in coffee is dangerous. And putting danger labels on everything could make people less likely to pay attention to the labels — like those on cigarettes — that really do matter.
The bottom line, for now, is that coffee retailers in California will have to post warnings. But that doesn't mean the evidence shows that coffee itself is risky.