It’s a question that plagues baristas around the world, and everyone seems to have an opinion on the subject.
According to materials chemist Christopher H. Hendon, the perfect brew comes down to three elements: water chemistry, particle size distribution produced by the grinder and coffee freshness.
Coffee is an acidic beverage, so the acidity of the water you use will impact on taste.
According to Hendon, “[b]rew water containing low levels of both calcium ions and bicarbonate (HCO₃⁻) – that is, soft water – will result in a highly acidic cup, sometimes described as sour.”
However, hard water will produce a chalky cup of coffee. Ideally, he says, the perfect cup of coffee will have water chemistry somewhere in the water. He suggests brewing your next coffee using a bottle of Evian to taste the difference.
Opinions differ over what constitutes the perfect particle size.
“One school of thought supports grinding the coffee as fine as possible to maximize the surface area, which lets you extract the most delicious flavors in higher concentrations,” Hendon explains.
“The rival school”, meanwhile, “advocates grinding as coarse as possible to minimize the production of fine particles that impart negative flavors. Perhaps the most useful advice here is to determine what you like best based on your taste preference.”
Finally, to get the very best out of your coffee, freshness is key. Gaseous organic molecules escape from coffee beans over time, which results in a less flavourful cup of coffee. Most cafes use freshly roasted beans.
Hendon suggests that coffee should be kept at home in an airtight container in the freezer to prolong freshness.
