The science behind the perfect cup of coffee
The qualities of the world’s most popular beverage rests on a combination of genetics, chemistry and physics. ARIELLA HEFFERNAN-MARKS looks at what goes into the ideal brew.
DIFFERENCES IN COFFEE TASTE are the result of plant variety, growing conditions and the processes used to prepare coffee beans – roasting, grinding and brewing.
The coffee bean is the seed of the coffee plant, located in fruit known as the ‘coffee cherry’. Classified as part the Rubiaceae family of flowering plants, there are more than 100 species within the Coffea genus, but only a few are cultivated commercially.
The most common is Arabica (Coffea Arabica), which accounts for about 70% of global production. The wild plant’s genetic homeland is Ethiopia, with the earliest evidence of cultivation for human consumption coming from 15th century Yemen. Since then the plant has spread, with human help, across the world’s tropical regions. Billions of Arabica plants, particularly in America, come from a single plant known as the ‘noble tree’ originally gifted to Louis XIV of France.
The balance of global production mostly comes from the ‘Robusta’ ( Coffea canephora) species. As its name implies, it is hardier and easier to grow, but less valued due to its more bitter taste. Indigenous to central and western Africa, it is now grown around the world in areas where C. Arabica does not do so well.
The genome of C. Arabica was only recently sequenced, while the first sequence of C. Canephora was completed in 2014. These analyses show coffee plants have larger families of genes relating to the production of alkaloids and flavonoids compared to species such as the grape and tomato. These compounds contribute to qualities such as aroma and bitterness.
The plant’s caffeine-making enzymes are more closely related to other genes within the coffee plant than to caffeine enzymes in tea and chocolate, which suggests its caffeine production abilities developed independently. What ecological reason is there to produce caffeine? One theory is the chemical helps repel insects or stunt competitors’ growth. Another suggests that pollinators may, just like humans, develop a caffeine habit.
Caffeine interferes with the action of adenosine, a vital neurotransmitter involved in sleep, by binding to the same receptors in the brain. As a result, the lethargic effects of adenosine are replaced by alertness.
In limiting the effects of adenosine, caffeine also allows other stimulatory neurotransmitters such as dopamine to work more effectively. The adrenal glands can also be triggered to release more adrenaline, heightening feelings of alertness.
It is coffee’s caffeine content that has arguably led to it becoming one of the world’s most valuable crops. But aroma and flavour have played a part also. Differences in these qualities can be traced to slight genetic variations that are the result of adaptations over time to different environments, as the plant has migrated around the world.