Garages, storage cellars, the fridge and other places which drop to low temperatures may place some potatoes in harms way once they are cooked at a later date.
At low temperatures, an enzyme called invertase breaks down the sugar sucrose in potatoes to glucose and fructose, which can form acrylamide during cooking. Frozen food doesn't carry this particular risk, as sucrose doesn't get broken down at very low temperatures.
The Food Standards Agency explains that when baked or fried, these sugars combine with the amino acid asparagine present in the potatoes and produce the chemical acrylamide.
Acrylamide is made by something called the Maillard reaction, which browns cooked foods and gives them their pleasing flavour. As sugars and amino acids react together, they produce thousands of different chemicals. Particularly high levels of acrylamide are found in starchy foods, like potatoes and bread, when cooked at temperatures over 120 C. The chemical can also be present in breakfast cereals, biscuits and coffee.
Acrylamide is a genotoxic carcinogen that's been linked to an increased risk of cancer. It was first confirmed that acrylamide caused cancer in 2002 by the Swedish National Food Authority, however many have long suspected that heating any foods to high temperatures can pose problems to long-term health.
In the body, acrylamide is converted into another compound, glycidamide, which can bind to DNA and cause mutations. Animal studies clearly show that acrylamide causes all sorts of cancers, but it's hard to relate this to us.
"Although evidence from animal studies has shown that acrylamide in food could be linked to cancer, this link isn't clear and consistent in humans," says Emma Shields, at charity Cancer Research UK.
It's much harder to study the effects of acrylamide in people, but there's no reason to think that it couldn't damage human DNA too. However, other lifestyle factors carry much more defined cancer risks. "It's important to remember that there are many well-established factors like smoking, obesity and alcohol, which all have a big impact on the number of cancer cases in the UK," said Shields.
A study by G. S. Pedersen and colleagues from Maastricht University in the Netherlands analyzed data from 62,573 women aged 55-69 when entering the study in 1986 and found that higher intakes of acrylamide were associated with higher risk of certain types of breast cancer compared to lower intakes.
During the 13-year-follow-up, 2225 cases of breast cancer were identified with hormone receptor status information available in 43 percent of the cases.
"We definitely believe acrylamide is a chemical to be concerned about," says George Alexeeff, deputy director for scientific affairs at the state Office of Environmental Health Hazard Assessment, the office that oversees implementation of Proposition 65. "Our general presumption is that unless there's some other evidence, we assume that if something causes cancer in animals, it causes cancer in humans."
The Environmental Protection Agency considers acrylamide potentially so dangerous that it has fixed the safe level for human consumption at almost zero, with a maximum permissible level in drinking water of 0.12 parts per billion.