Updated: Nov 15, 2022
Some of you are probably missing high quality freshly brewed coffee during the lock-down. For many of us coffee drinking is part of our lifestyle and a daily habit.
Although flavour, aroma and caffeine content typically determine our tastes, coffee is a complex chemical mixture, containing thousands of different compounds including minerals, alkaloids and polyphenols. High content in polyphenols and other biologically active compounds in coffee beans explains coffee’s amazing antioxidant properties.
It’s been suggested that caffeine might have a synergistic effect with other components in coffee to produce the overall neuroprotective effect. Polyphenols and flavonoids in coffee also were reported to have anti-allergic, antimicrobial and anti carcinogenic properties. Coffee intake, but not caffeine, has been recently shown to have anti-aging effects through telomere lengthening activity.
Although it’s so tempting to discuss the effects of coffee on health and disease, this post is rather about different varieties of coffee beans, brewing methods and its bioactive compound concentration.
The total polyphenols content in coffee varies depending on the type of beans. Popular coffee substitute – Chicory root coffee has much lower content of polyphenols. Other coffee surrogates such as rye, barley, dandelion, carob, dried figs and oak seeds contain no caffeine and also have low polyphenolic content. However, carob coffee seems to have the highest level of antioxidant compounds among surrogate coffees.
Good old Robusta and Arabica – the two most world’s consumed types of coffee have different tastes and different bioactive compounds contents.
Coffee made from Robusta beans (accounting for quarter of world’s consumption) is more concentrated, bitter and less aromatic with the highest content of caffeine. Green coffee beans of Robusta have 2-folds higher antioxidant than Arabica, but after roasting this difference is reduced.
Coffee from Arabica (which accounts for more than 70% of world’s consumption) has superior sensory quality due to higher content of aromatic oils, and it has half the caffeine content than Robusta. Arabica coffee contains higher levels of fat-soluble compounds kahweol and cafestol, which have significant health benefits. Although, a higher amount of cafestol in unfiltered coffee has been associated with increased cholesterol level. Note that the world’s best coffee is made from 100% Arabica beans.Coffee beans from organic and conventional farming have different caffeine content. Conventional coffee contains significantly more caffeine and also less polyphenols than organic.
Roasting degree also has an impact on polyphenols concentration.
Up to 60% of their concentration (compared to green coffee beans) can be lost depending on the intensity of roasting thermal process. Go for light or medium roasted coffee beans – it’s guaranteed to have the highest antioxidant capacity.
Note that the concentration of chlorogenic acids (CGA) (the main polyphenol family in coffee) in dark roasted Robusta is 14-fold lower than in green raw beans, while in Arabica it’s about 5-fold.
Although the natural antioxidant compounds are reduced during the roasting process, new non-enzymatic browning compounds (e.g. melanoids) are formed. They have been found to have an antioxidant activity, but their contribution doesn’t seem to be significant.
Interestingly, the brewing methods also impact the efficiency of extraction of polyphenols from ground roasted beans. For example, filtered coffee, the most widely consumed brew, prepared by pouring boiled water over ground beans in a paper filter has lower polyphenol concentration than espresso coffee.
Moreover, brews prepared by boiling water without filtration (think Turkish/Greek coffee) has a higher polyphenol content than the corresponding filtered ones. Surprisingly, instant coffee doesn’t seem to contain less polyphenols than filter or Turkish coffee, but research is not consistent on its ranking among various types of coffee.
Another surprising factor that researchers investigated was the Reheating of prepared Turkish/Greek coffee to a boiling state increases the content of CGA and caffeine when compared to initially prepared brews.
Decaffeinated coffee brews generally have 20-30 % lower antioxidant properties than regular brews. It seems that the decaffeination process does significantly impact the content of polyphenols.
Adding milk into coffee to abate caffeine effect or to ameliorate the taste alters the bioactive composition and antioxidant activity of coffee brew. Research shows that in vitro antioxidative capacity is decreased, when milk is added to espresso. Similarly, macchiato and latte have lower phenol contents.
So few practical considerations:
Type of beans? If you can grind your coffee at home, it’s best to buy whole arabica or robusta beans and not pre-ground because once the hard-outer shell protecting bean is broken, the oxidative process begins damaging coffee properties.
Expiry day? Purists advise to buy freshly roasted beans, so look at roast day, if available. After the roasting process, beans begin to release carbon dioxide called degassing. Degassing affects aromatic oils, by diminishing the flavor of coffee beans. For those enjoying a simple brew of boiling water over coffee or espresso, beans in their first 2 weeks after roasting seem to be generally optimal. But let’s be realistic, unless you live in Hawaii, Brazil or Ethiopia near coffee plantations or have close friends in this business, it’s almost impossible to have freshly roasted beans.
How to store coffee beans? Keep your beans in a dark, dry, cool place in airtight glass or metal containers. Treat it as a bottle of expensive wine! And don’t put it in a fridge, coffee cells structure is porous so it absorbs various aromas and may condensate in cold and damp environments.
Researching about coffee gave me more confidence that freshly brewed cup of coffee in the morning has more benefits than harm unless you suffer from serious diseases or have a genetic polymorphism responsible for abnormal caffeine metabolism in the liver. And as always in nutrition, it’s all about balance and adequate consumption.