Acrylamide is the black, burnt stuff that can form on some foods that contain sugars and certain amino acids when cooked at high temperatures, such as frying, roasting, or baking (boiling and steaming usually don’t produce acrylamide). Past studies have singled out potato chips, burnt toast, and french fries as vehicles for the chemical. Acrylamide also forms in coffee when the beans are roasted.

The Food Standards Agency has suggested people should only fry, toast, roast, or bake starchy food until it is a golden color, being careful not to burn it.

Concerns about acrylamide have been around for decades. In one experiment that detailed in a 1986 issue of the journal Toxicology and Applied Pharmacology, lab rats were given regular doses of acrylamide through drinking water for up to two years. A selection of rats were euthanized and examined after six, 12, and 18 months of exposure. Studies of the animals’ brains, hearts, kidneys, livers, and testes revealed degenerative changes for all three groups; tumors were more likely to develop in the rats the longer they were exposed.

In April 2002, scientists at the Swedish National Food Administration and Stockholm University reported finding the chemical in a bunch of fried and oven-baked foods. The body of evidence related to the effects of acrylamide in food is still incomplete, but because it had an adverse reaction in rats, scientists and public health agencies in numerous countries have since labeled it as being “a probable human carcinogen.” In 2010, the US Environmental Protection Agency published a report (pdf) agreeing, concluding acrylamide as “likely to be carcinogenic to humans.”

Over the years, the acrylamide issue has seeped into public conversation only rarely, though in some cases it has turned into a high-profile issue. For example, in 2010, a lawsuit was filed against Starbucks in California to try and get the company to label its coffee products as containing a carcinogen. The company lost in its first defense of that case, but has since appealed.

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