When I started my PhD studies 4 years ago I did not like coffee. Now, I actually rather like the aroma of freshly brewed coffee and sometimes I even seriously consider drinking it. You might think that this is due to the long working hours associated with working in science but I think it is because there is a coffee machine in my office right behind my desk. Throughout the day there is a steady stream of coffee making around me so for the last four years I have spent my working week surrounded by a lovely coffee aroma. Although I’m still hoping to avoid becoming a coffee drinker I realised that the sum total of my knowledge of where coffee comes from is “roasted coffee beans”. So I did some research…
Coffee is made from the beans of members of the Coffea genus. Coffea plants are evergreen shrubs/small trees that grow to about 5 m tall, although when cultivated they are usually much shorter due to pruning. The beans are contained within the fruit, known as “cherries”. After harvesting the soft flesh of the fruit is removed and the beans fermented to remove the mucilage (a slimy substance) leaving the bean. The beans are then dried and roasted before they are ready for coffee making.
Coffea plants originate from Ethiopa. According to legend, in the 9th Century a goat herder called Kaldi stumbled across a group of monks while he was searching for his flock of goats (1). The monks were eating the cherries from a Coffea plant. Kaldi danced with delight when he tasted the cherries and shared them with a passerby. The passerby took them to his monastic friends who cultivated the tree and brewed a drink that enabled them to stay wide awake during prayers (1). Whether or not this story has any element of truth in it, there is evidence that coffee was cultivated in the Sufi monasteries around Mocha in the Yemen as far back as the 15th Century (2).
Today the coffee industry is huge with coffee produced in equatorial regions across the world (2). In 2005, it was the seventh-largest legal agricultural export worldwide (2). Of this, Coffea arabica accounts for 70% of coffee production but C. canephora (also known as robusta coffee) also widely grown.
Coffee contains the stimulant caffeine. The caffeine content of coffee beans varies but in C. arabica is typically around 1.2% of its dry weight. C. canephora has a higher caffeine content and tastes more bitter so varieties of C. arabica are usually the bean of choice for high quality coffees. However, C. canephora is less susceptible to disease and can be grown in lower altitudes and warmer climates than C. arabica (2) so it is often used in cheaper coffees.
There is increasing demand for decaffeinated coffee. To reduce the caffeine content unroasted (green) beans are steamed and then rinsed with a solvent to extract the caffeine (2). This process is repeated 8-12 times until the caffeine content has been sufficiently reduced for the beans to be classed as “decaffeinated” (in EU 99.9% caffeine free by mass) (2). Scientists have found some mutant C. arabica plants that have naturally low caffeine content (3). Caffeine is made from its precursor theobromine through the activity of the caffeine synthase enzyme. The mutants lack a functional caffeine synthase so accumulate theobromine instead (3). Cultivating naturally low caffeine plants would remove or reduce the need for the decaffeination process so naturally there is a lot of interest in this research.
1) Laws, B. (2010) Fifty plants that changed the course of history. Pub: David and Charles.
2)Wikipedia: Coffee http://en.wikipedia.org/wiki/Coffee (retrieved 12/01/14)
3) Silverolla et al (2004) Plant biochemistry: A naturally decaffeinated arabica coffee. Nature.