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.

Cosmos - - Coffee -

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.

CREDIT: NEIL FLETCHER & MATTHEW WARD / GETTY IMAGES

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