The Science of Good Coffee (Part 2)

If you’ve been paying attention, you’ll know we recently covered two of the four equally important variables that separate a great cup of coffee from your average brew.

We focused solely on the beans – both the beans themselves and the way they are roasted. We learnt that the type of bean – Arabica or Robusta – greatly influences the taste and level of bitterness in the coffee and that the way these beans are subsequently roasted will either enhance or diminish those flavours.

Let’s conclude our exploration into what goes into a good cup of coffee by looking at the final two elements: the grind and believe it or not, the water.


You may recall the famous scene in the 2002 film Black Hawk Down, where Ewan McGregor’s coffee-obsessed character Grimes explains how the coarseness of the grind is of the utmost importance. “It’s all in the grind,” he says. “Can’t be too fine, can’t be too coarse. This, my friend, is a science.”

He’s not wrong. The way your coffee is ground – its fineness or coarseness – has a significant impact on how your coffee will taste. The level of coarseness impacts the way water flows through the ground beans. Take for example Turkish coffee, which is very finely ground and famously strong and bitter.

This is because the fineness allows water to extract the compounds within the grind. Conversely, if the grind is coarser, your coffee may end up tasting weak and watery. As a study by The Conversation pointed out, ideally your grind will be somewhere in the middle. As McGregor said, it “can’t be too fine, can’t be too coarse”.


If coffee is a science experiment all its own, the same could be said for the water used to brew it. Everything from the purity of the water used to the temperature of the water and the amount of time the coffee and water are left to brew for ends up impacting a cup’s flavour.

Let’s start by busting a myth: purer water does not necessarily result in better tasting coffee.

It’s easy to fall into the trap of assuming pure, distilled water clear of any potential contaminants or additives will do the least to ‘taint’ your coffee, but one study reported on by Coffee Analysts found calcium and magnesium, commonly found in ‘hard water’, actually do a lot to capture the natural flavours of coffee beans.

As for temperature, one of the more popular recent coffee trends is cold brewed coffee, which is made by placing ground coffee in ice water and leaving it to brew in near-zero temperatures for a period of time. Because of the very low brewing temperature and its effect on the caffeine and acids in the beans, the result is a coffee that is generally less bitter than coffee made with hot or boiling water.

Brewing coffee with hot water, on the other hand, means the compounds in the beans are extracted very quickly and if the water used is very hot, certain compounds can even be evaporated in the steam, resulting in a weaker, less flavourful cup.