Cosmos - - Coffee -

Brew­ing is the fi­nal and most vi­tal step in the cof­fee-mak­ing process – the one we are all a bit more fa­mil­iar with.

While there are dif­fer­ent ways to achieve the same end, the es­sen­tial process in­volves soaking cof­fee grounds in hot wa­ter suf­fi­cient to al­low the flavour-pro­vid­ing mol­e­cules to dif­fuse into the sur­round­ing liq­uid.

A sci­en­tific ap­proach to the chem­istry of cof­fee brew­ing was pi­o­neered by Mas­sachusetts In­sti­tute of Tech­nol­ogy pro­fes­sor Ernest Early Lock­hart, who in the 1950s left an aca­demic ca­reer in food tech­nol­ogy to be­come re­search di­rec­tor of an or­gan­i­sa­tion known as the Cof­fee Brew­ing In­sti­tute. He cre­ated the “Cof­fee Brew­ing Con­trol Chart” for brew­ing the ideal cof­fee, bal­anc­ing sweet­ness and acid­ity.

Lock­hart’s ba­sic for­mula de­pended on two ba­sic fac­tors. The first is the ex­trac­tion or ‘sol­ubles yield’, which is the amount of cof­fee chem­i­cals ex­tracted from the cof­fee grounds. This is af­fected by brew­ing method – grind, wa­ter tem­per­a­ture and time – and ex­pressed as a per­cent­age. The sec­ond is the strength or the con­cen­tra­tion of solids dis­solved in the brew, which is also ex­pressed as a per­cent­age.

Lock­hart’s chart, de­vel­oped through sur­vey­ing cof­fee drinkers about their cof­fee pref­er­ences, rec­om­mended 18-22% bean ex­trac­tion and 1.15-1.35% dis­solved solids strength for the per­fect brew. The ‘golden ra­tio’ was 17.42 units of wa­ter to 1 unit of cof­fee.

Con­sid­er­ing how im­por­tant tem­per­a­ture seems to play in the brew­ing process, this raises the ques­tion of the ‘cold brew’ and how it still man­ages to cre­ate a de­li­cious and en­joy­able cof­fee.

It all links back to the process of dif­fu­sion – which re­lies on tem­per­a­ture but also time. Lower tem­per­a­tures re­quire longer time: the mol­e­cules still move out of the ground cof­fee, but over a greater time pe­riod.

This can cre­ate an even more aro­matic cof­fee by al­low­ing other chem­i­cals to form that nor­mally would not dur­ing the hot­brew­ing process.


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