Skip the third cup of coffee – or not

A cup of coffee to raise the spirit.

A cup of coffee to raise the spirit.

Do you need a cup of coffee in the morning like me to start functioning? To kick-start the brain and get the spirit up. Do you also have a refill after lunch? To be honest I am tempted to have a third cup in the afternoon as well, but then I remember the furan issue.

You haven’t heard about furan? Lucky you. If you read on I am going to destroy the enjoyment of your final cup of coffee for the day – or not.

You might have read the previous blog on acrylamide formation in which you had to take most of the blame for this toxic compound found in your toast. With furan it is actually a shared responsibility between you and the coffee roaster unless you roast your own coffee. And not many would do that.

First some technical facts about furan

Furan is a highly volatile substance formed in foods and beverages due to the degradation of naturally-occurring sugars, polyunsaturated fatty acids and ascorbic acid (vitamin C) during heating. It is actually an integral component contributing to the sensory properties of the heated product and is seen as an important coffee flavour component. However, in 2004, the US Food and Drug Administration (FDA) raised concerns about the presence of furan in food and beverages.

Already in 1993 furan was subject to comprehensive toxicological evaluation within the US National Toxicology Program (NTP). Results showed that furan was carcinogenic and mutagenic in animal experiments. High doses of furan given to rats and mice caused the formation of liver tumours. It is also expected to be genotoxic, a particular danger sign, and a warning has been issued that it might be a possible human carcinogen. More research is underway to confirm the previous findings, but overall currently not good news on this front.

Furan levels in coffee

Roasted coffee beans have the highest furan levels (Photo: MarkSweep)

Roasted coffee beans have the highest furan levels (Photo: MarkSweep)

Although furan can be formed in different heated foods and beverages, coffee is the outstanding contributor to furan exposure in adults. A survey by the European Food Safety Authority found that roasted whole coffee beans have the highest levels of furan, followed by roasted ground coffee and instant coffee powder. The darker the roast, the higher the furan levels. So that’s the industry side and it is not much they can do while retaining the coffee aroma.

But as it happens it is also important how you prepare the coffee brew. When Spanish researchers compared the effect of different brewing methods they found the highest furan levels in coffee made from capsules followed by commercial bean-to-cup machines in which the coffee was prepared from start to finish in a largely enclosed environment. Less furan was found in coffee made in drip coffee machines and the least in instant coffee.

There is an easy explanation to the findings. The hermetically-sealed capsules prevent the highly volatile furan from being released, and the coffee machines used to brew this coffee use hot water at higher pressures, which leads to more of the compound being extracted into the brew. Similarly, the enclosed system in automated espresso machines transfers more furan to the final brew. This is great for the coffee taste but may be bad for health.

But there are some good news

Because of the volatility of furan, the longer the coffee brew is exposed to air in cups or jugs the more of the furan will evaporate. So maybe you should let the coffee cool down a bit before drinking it. You might also avoid to take a sniff of the newly brewed coffee though, as good as the smell might be.

And there is more. Confusingly, a recent review of epidemiological data found that three cups of coffee per day actually reduced liver cancer risk by more than 50%. It was speculated that this favourable effect might have been mediated by coffee’s proven prevention of diabetes, a known risk factor for the disease, or for its beneficial effects on cirrhosis and liver enzymes. A further epidemiological study showed that four or more cups of coffee a day was associated with a lower risk of prostate cancer recurrence and progression. Men who drank that much coffee daily had a 59% reduced risk for prostate cancer recurrence or progression, compared with those who drank one or fewer cups per week.

So what to believe? It is proven that coffee contains phytochemical compounds with beneficial effects on health. That include anti-inflammatory and antioxidant effects and modulation of glucose metabolism, but also some anti-cancer effects. Could that weigh up the potential negative effects of furan?

Maybe I should have the third cup of coffee anyway.

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