The coffee extraction process: Here’s what to look for

The coffee extraction process- Here’s what to look for

Andrea Illy, an Italian businessman and chairman of Illy coffee, once said:

‘Espresso is a miracle of chemistry in a cup.’

And he’s got a good point. When it comes to making espresso-based coffees like Lattes, Cappuccinos and Macchiatos, there’s a lot more to consider than the pretty rosetta on top. Underneath that layer of microfoam is a world of chemistry in a cup, and you need to get your coffee extraction right to produce a well-balanced up.

In this blog post, we’ll highlight some of the key extraction metrics you need to consider so you can start pulling the perfect shot.

Variable #1: Type of coffee

This is an obvious one…

Of course, the type of beans you run through your espresso machine will make a big difference to flavour profiles. Whether it’s a single origin, a blend, robusta beans, arabica beans, beans from different farms… the list goes on.

Most high-quality espresso from specialty shops will be of single origin (i.e. a coffee from one singular farm, not blended with different varietals). For example, a single-origin Equinox Espresso from Kenya (imported by Royal Coffee) will produce a different set of flavours than a La Florida ‘Acevedo’ from Colombia (imported by APEX), for example.

Your bean of choice will impact every other variable in the coffee making process, too. You must consider things like:

  •      The roast date of the coffee.
  •      The flavour profile of the coffee.
  •      The region the coffee comes from.
  •      How you’ve stored your coffee prior to extraction.

Factors like these will affect the consistency of flavour. For example, if you’re using an older single-origin, it might require a higher water temperature to ensure you produce a balanced flavour in the cup.

Variable #2: Coffee grind size

The next variable to consider when extracting a shot of espresso is how finely or coarsely you grind your coffee. Again, this variable will influence every other variable in the extraction process.

If you have an older coffee in your hopper, for example, you might consider a finer grind rather than a coarser grind. This is because, as a coffee ages, it loses flavour. A finer grind might mean that water has to work harder when passing through a porter-filter, which in turn might result in a greater extraction of flavour.

The same can be said for coffees with more subtle flavour profiles. It might require a finer grind to extract more flavour from the coffee.

These examples, however, aren’t set in stone. Rather, personal preference and other extraction variables will determine how finely or coarsely you grind your coffee from espresso extraction. It’s a matter of tuning your machine accordingly.

Variable #3: Water temperature

Water temperature (and water type) for that matter, will influence your coffee extraction, too. According to Solo Coffee, the ideal machine temperature for a balanced extraction is between 90.5 and 96 degrees Celsius. As ever, though, this variable also depends upon every other variable. We’re talking chemistry here…

Andrew Easthope of Five Senses Coffee conducted a study on water temperature to determine the ideal water temperature. He sampled 40 espresso shots against four different water temperatures and found that the yield percentage (the total amount of extracted elements from the coffee) increased as the temperature of the water increased. However, at 98 degrees Celsius, the yield percentage began to decrease.

Consider this as a good sense of judgement: In most instances, too low a temperature will likely under extract a coffee and produce a sour, vinegary flavour profile. Too high a temperature will likely result in over extraction, and produce burned, bitter flavours. You’re looking for that sweet spot in the middle.

Variable #4: Extraction time

When it comes to extracting an espresso, the length of time you run a shot for will heavily influence your flavour profile. This is often the final variable to consider when dialling in your espresso. However, if your flavour profile isn’t living up, you might consider re-tuning your machine.

If we focus only on time, a coffee extracts different elements throughout the extraction process. Often, a long extraction will result in your coffee ‘blonding’ (when your coffee turns from that silky chestnut to watery blonde), which will likely lead to over extracted flavours like bitterness.

The optimum extraction time lies between 20 and 30 seconds a shot, but this is not mandatory.

Variable #5: How you tamp

Yes, even the pressure you apply to your coffee when you tamp will affect the extraction process. If you fail to achieve an even tamp, for example, it means that your coffee won’t extract evenly, and you’ll end up with ‘channelling’ (where water follows the cracks in your coffee ‘puck’), and channelling will cause inconsistent, unbalanced flavour profiles.

Caffe Society have produced an excellent guide on how to tamp coffee. In short, the process is:

  1. Give your group handle a quick shake
  2. Place the group handle on a clean flat surface or tamping mat
  3. Tamp with a light amount of pressure to compact the ground coffee a little
  4. Let the puck rest for a moment
  5. Now tamp the ground coffee again with around 8lbs of force
  6. OPTIONAL: Rotate the tamper to ‘polish’ the shot
  7. Withdraw to reveal a smooth, even and compacted puck

Simple, right?

Personal preference: the ultimate variable

There are many other variables at play with coffee extraction. The machine you use, the BAR pressure the machine produces, your dose size… Even the temperature of your cup will affect the flavours of your coffee.

The biggest variable, however, is personal preference. Yes, coffee extraction is practically a rocket science, and there’s no argument that an under or over-extracted cup of coffee produces some disgusting results, and sure enough, a balanced coffee is a good coffee.

But who defines disgusting? Anything can taste good if you give it to the right person…

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