GRIND­ING

Cosmos - - Coffee -

Cof­fee grind­ing is what al­lows us to taste the flavours de­vel­oped in a cof­fee roast. It is vi­tal for de­ter­min­ing the strength of your brew.

It ap­plies the same chem­i­cal prin­ci­ple that our hu­man cells use to sur­vive: in­creas­ing sur­face area and min­imis­ing vol­ume im­proves the rate at which mol­e­cules can pass in and out.

Grind­ing the beans into tiny frag­ments in­creases their sur­face area and de­creases their vol­ume. This in­creases the rate and num­ber of flavour mol­e­cules that can move out of the bean. The finer the grind, there­fore, the stronger and tastier your cof­fee.

Popular wis­dom is that grind qual­ity is de­ter­mined by three fac­tors: mois­ture, roast and ori­gin of the beans. The the­ory is that the drier the bean the eas­ier it is to cut into small pieces, thus pro­duc­ing more flavour; a darker roast means more brit­tle beans, which break more eas­ily into smaller par­ti­cles; and the ori­gin of the bean af­fects its phys­i­cal prop­er­ties, in­clud­ing how well it dries out and its abil­ity to be cut.

Like much re­ceived wis­dom, how­ever, these ideas have been chal­lenged by sci­ence. Re­search into the fac­tors af­fect­ing cof­fee-grind qual­ity has found the piv­otal is­sue is tem­per­a­ture.

“Grind­ing colder cof­fee beans pro­duces a more uni­form par­ti­cle dis­tri­bu­tion, with a de­creased par­ti­cle size,” con­cluded a 2015 study by an in­ter­na­tional team of sci­en­tists led by Christo­pher Hendon of the Univer­sity of Bath. “While the de­creased par­ti­cle size will tend to speed up ex­trac­tion due to the larger sur­face area, the in­creased uni­for­mity should min­imise the amount of wasted bean, which is dis­carded with­out be­ing ex­tracted to com­ple­tion.”

A rea­son, per­haps, to go for the trendy ‘cold brew’ over the tra­di­tional hot espresso!

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