When we run training sessions for new baristas, we like to start off with a little experiment. We prepare a double espresso on our Marzocco, but instead of letting it all pour into the same cup, we let the first third pour into one cup, then quickly switch to a second cup for the next third, then do the same again to put the last third into a third cup.
Then we taste each one. And the results tell us a great deal about what it takes to make a great coffee – and how to ruin one.
No prizes for guessing the first difference: intensity. The first one hits you with a punch, the last one is a bit weak and the second one is, of course, between the two. But what’s more surprising is that they also taste different, as if they’re different coffees. The punch from the first one comes not just from the intensity but a high acidity level. It might be a nice acidity, like one that you get from a fresh piece of fruit, but it’s a bit harsh for most people. On the other hand, flavours and aromas are largely absent from the last one. It’s softer but a bit flat and uninteresting.
The reason for is that coffee beans are made up of many different organic components – sugars, proteins, organic acids, volatile aromatic compounds and so on – each with different levels of solubility. The more soluble elements come out first, such as organic acids that are so present in the first third of the espresso. The last third contains few highly soluble elements, because they’re already gone, but more of the less soluble elements which took longer to fall into the cup.
So what? you say! Well, regardless of the science, there is one important lesson in all this for anyone making a coffee : the extraction time, or the time the water takes to pour through the coffee, makes all the difference to the taste. You can take the best coffee in the world, one that’s perfectly roasted, and use an espresso machine that cost you a small fortune. But if the extraction is too fast or too slow, the result can still be unpleasant - too acidic, too bitter, rough or lacking flavour.
Which then opens up a whole new topic of discussion about how to control extraction time! It’s a simple question with many complicated answers. But there is one very good place to start.
All other things being equal, a finer grind of coffee will present more resistance to the water flowing through, slowing it down. On the other hand, if you want to speed up your extraction time, use a slightly coarser grind.
The trick is to play around with it, trying different grinds and tasting the difference in the cup, until you get the balance you like the best.
It’s what good specialty coffee shops are doing every day.
