Can coffee really give you cancer?

On 7 May 2018, a Los Angeles Superior Court Judge ruled that cups of coffee sold in California will have to carry a label warning customers about the potential cancer-causing effects of their favourite morning beverage. 

The basis of the decision was that coffee companies such as Starbucks, Green Mountain Coffee Roasters, Kraft Foods Global, and JM Smucker failed to show sufficient evidence that there was no significant cancer risk posed by just one particular chemical in roasted coffee – acrylamide.

What is acrylamide?

Acrylamide is a small organic molecule with a formula C3H5NO. This chemical is mainly used in industrial processes, such as making paper or plastics, and more recently, the Swedish National Food Administration found it to be present in roasted or toasted foods, including coffee. Because people can be exposed to acrylamide in their diet, at their workplace, or through cigarette smoke, scientists carried out a number of studies to find out if acrylamide could possibly cause cancer. 

There are two main ways to test if contact to a certain chemical such as acrylamide can be linked to increased incidences of cancer. 

In a laboratory, animals, mainly rodents, are exposed to large quantities of the compound in question to test if they develop cancer. Similarly, human cells in petri dishes can be treated to generous helpings of the potentially risky material. While these studies can be helpful, they have a few limitations. First, rodents and humans might not react to a chemical in the same way, and second, a substance may be toxic in high concentrations but still be quite harmless in small quantities. 

As such, lab tests need to be complemented by large studies in groups of people to credibly link the substance to an increased risk of cancer. During these long-term studies, scientists track the incidence of cancer in groups that were exposed to the chemical to groups that were not, as well as the general population. The outcomes can still be ambiguous because there are many other lifestyle factors that can skew results.

Is acrylamide carcinogenic? 

Based on both types of studies, it is still unclear if acrylamide is really a human carcinogen. Laboratory tests in rats and mice showed that these animals developed significantly higher rates of cancer when they had been given 1000 to 10,000 times more acrylamide than what most people get exposed to from their diet. If animals are affected, it is reasonable to be careful with human exposure, which is why the International Agency for Research on Cancer listed acrylamide as a probable human carcinogen. The United States Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) have both classified acrylamide as a likely human carcinogen. The EPA has also regulated acrylamide levels in drinking water, but there are currently no FDA regulations in place for acrylamide in foods. 

How does acrylamide get into coffee? 

Green coffee does not contain acrylamide. It is formed during roasting as a by-product of the Maillard reaction. In this process, sugars and amino acids combine to produce the brown colour and much of the aroma of roasted coffee. Unfortunately, while the Maillard reaction is essential for creating delicious coffee, it is also responsible for the acrylamide controversy.   

So if acrylamide is produced in the Maillard reaction, does darker roasted coffee contain more of it? Researchers tested various combinations of roast times and temperatures to find out. They found that roast temperature by itself did not have a measurable effect. All viable roast temperatures are high enough to create acrylamide. The more important question was, how long did the coffee spend at those high temperatures? 

Somewhat counter-intuitively, short roast times were found to yield more acrylamide than longer ones. This happens because acrylamide concentration reaches a peak very early on in the roast cycle (around two minutes), then decreases as the roast progresses further. In fact, roasting creates acrylamide, but it also destroys it.

By the end of a typical roast cycle, most of the acrylamide degrades, leaving 5 to 10 per cent of the peak concentration behind. This might sound like a big difference, however it turns out that roasting darker only yields a marginal advantage. The acrylamide peak is so early on in the roasting process that after about 2.5 minutes, there is no significant difference between roasts. At the same time, roasting time has a large impact on sensory properties, and roasting dark can also create other undesirable compounds. 

When comparing Arabica and Robusta, some researchers found that slightly more acrylamide was created in Robusta coffees. However, this has not been confirmed by others. Interestingly, grain-based coffee substitutes, such as chicory were found to contain more acrylamide than roasted coffee.

Storage and brewing

During coffee storage, acrylamide continues to degrade over time. Higher storage temperatures accelerate the destruction of acrylamide. At room temperature, losses of 40 to 60 per cent have been recorded in over a period of six to 12 months, while cold storage preserved acrylamide better. This is neither surprising, nor particularly helpful. Chemical reactions, including those responsible for staling and aroma loss, proceed faster at higher temperature. The trade-off is hardly worthwhile. 

Acrylamide is a polar molecule and as such, is efficiently extracted with hot water. Instant coffee and drip filter brewing allows for near complete extraction of acrylamide from the ground coffee into the brew. Acrylamide is not quite fully extracted into espresso due to a higher brew ratio and a shorter extraction time. 

How to reduce acrylamide intake in coffee

Up to a quarter to a third of our acrylamide exposure from dietary sources comes from coffee. As discussed above, there are only limited options to reduce acrylamide  in coffee and even these would all significantly affect sensory properties.  

The only option left for those really worried about acrylamide is drinking less coffee. However, these concerned customers might miss out on many other health benefits. From where science currently stands, the health benefits of coffee, consumed in moderation, outweigh the risks. While acrylamide is classified as a possible human carcinogen by a number of expert agencies, coffee is no longer. In 2016, the cancer agency of the World Health Organisation took it off the list as a “possible carcinogen”. 

At the end of the day, do not let warning labels put you off coffee. There are many other foods we can easily prepare in a way that that minimises acrylamide exposure. While you’re enjoying a cup with your breakfast, don’t forget to check that your toast does not get burnt to reduce further exposure to sneaky Maillard by-products. 

By Dr. Monika Fekete, Found of Coffee Science Lab. 

This article appears in the June edition of BeanScene.subscribe now.