A fresh cup of climate change

What happens to our coffee beans as CO2 levels and temperatures rise?

A prevailing debate throughout the centuries is the choice between two morning staples: coffee or tea? While tea may be a valid option, coffee lovers, particularly the sleep deprived students in town, will probably tell you that nothing is better than waking up to the tantalizing smell of a freshly brewed cup of coffee.

The aroma of a coffee bean is just one of the qualities explored in a recent study examining the potential impacts that climate change could pose on this beloved morning beverage. Led by Dr. José Ramalho, a researcher at the University of Lisbon, this study set out to understand the characteristics of bean quality related to taste, acidity, bitterness, and astringency. Ramalho and colleagues focused on the changes to the chemical composition of the beans when their growth environment was altered by increasing temperature and carbon dioxide (CO2) levels, two important components expected to shift during climate change.

The length of time coffee beans take to mature is key to the flavour of the beverage. The maturation time can be accelerated by increasing temperature, which has been shown to affect flavour. Slow maturation, at lower temperatures, allows for the accumulation of aroma precursors to produce a more well-rounded flavour. Balancing concentrations of different compounds will contribute to overall taste, such as the amounts of sugar and minerals, whereas high levels of caffeine and trigonelline negatively affect flavour. Other compounds, like lipids, affect texture, and while chlorogenic acid contributes to desirable antioxidant properties, it can also affect the astringency and bitterness.

Not only does increased temperature shorten maturation time, it also has been shown to result in the accumulation of compounds that are associated with negative flavours. This sentiment is echoed by Anne Winship, the owner of Bean Fair, a fair-trade coffee supply company based out of Quebec. Winship said that, in the context of climate change, “because coffee grows best in cooler temperatures at high altitudes, crops may have to eventually be planted higher up” in response to increasing temperatures, as “crops that ripen more slowly are generally acknowledged to be better tasting.” 

Interestingly, Ramalho and colleagues’ research found a curious interaction when they looked a little deeper. Increasing CO2 levels during plant growth, on its own, was not seen to have a significant impact on the quality of coffee. However, they found that although increased temperature was the instigator for most of the changes in chemical and physical characteristics of the beans that resulted in lower quality coffee, this effect could be mitigated by elevated concentrations of CO2. It seems that beans grown in conditions with high CO2 and increased temperature produced coffee that was closer in quality to those grown in controlled temperature conditions, and much better than those grown solely at high temperatures.

These findings come as both a blessing and a warning with rising temperatures and other factors associated with climate change. Ramalho states that “in global terms, many regions, especially those at lower latitudes, will be less adequate for [coffee bean] agriculture as changes will become more unpredictable in terms of heat and drought events.” These negative aspects of increasing temperature also have other consequences on coffee agriculture, echoed Winship when she voiced concern over the threats that producers will have to face as “plants may be more susceptible to certain diseases, specifically coffee-leaf rust.”

There is a silver lining.“The impact of temperature and drought might be somewhat mitigated by CO2, even if the global situation is still negatively affected,” says Ramalho.

While we know there is a lot to worry about regarding climate change, at least we can tackle the problems with a fresh cup of hot coffee in hand–maybe even one from our favourite Sackville café–and not have to worry about it leaving us bitter.


To learn more, the original research article ‘Can Elevated Air [CO2] Conditions Mitigate the Predicted Warming Impact on the Quality of Coffee Bean?’ can be found here: https://doi.org/10.3389/fpls.2018.00287


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