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So you’ve started using your new coffee grinder and espresso machine, and the espresso you’re producing is sour, watery and coming out far too quickly, or it’s thick, bitter and taking far too long. Perhaps you’ve had a visit from your wholesale coffee supplier who helped you ‘dial-in’ your espresso grinder for the perfect double shot, but a few days later and you’re bashing your head against the wall once again.

Grind size is one of the most frustrating aspects of brewing espresso, but once you’ve got the hang of it and recognised that it’s an ongoing battle, rather than a one-time fix, chasing the perfect grind size becomes part of the fun in brewing great coffee.

In this article and accompanying video, we’re going to discuss why grind size is so important to your coffee, how a change in grind size affects your coffee, and how to calibrate your coffee grinder for the perfect shot of espresso.

How To Dial-in an Espresso Grinder

For the purposes of this guide, and to keep it simple, we’re going to be working off of a basic standard recipe for a double shot of espresso.

Things you’ll need:

  • A set of weighing scales accurate to 0.1g
  • A timer (built into the scale or external)
  • Your espresso machine and coffee grinder
  • Fresh roasted coffee (1-3 weeks past roast date)

The recipe:

  • 18 grams of finely ground coffee
  • 38 grams of liquid espresso output
  • A brew time of between 26-30 seconds.

The weighing scale is potentially the one item you’ll need to purchase, but is essential in creating a consistent coffee. Your grinder may not dispense a consistent amount of ground coffee, so using a scale helps to combat this issue. Inconsistent dosing of coffee is one of the main problems we see with paddle coffee grinders.

Before Dialling in Your Grind Size

Make sure you are setting yourself up for success by levelling out your coffee bed and tamping evenly every time. This is commonly referred to as ‘puck prep’. In it’s most basic form, you can use the palm of your hand to gently knock the side of the portafilter, breaking down and large clumps of coffee grounds and creating a flat bed of coffee. This is then followed up by a nice level tamp, creating a level surface on the grounds and pushing out any pockets of air. This can be made even simpler and more efficient by using automatic tampers like the PuqPress.


Run a Test Shot of Espresso

Every day, even at the same grind setting as the day prior, your espresso is likely to come out differently. This is due to a host of factors including the freshness of your coffee, the ambient temperature and humidity in the café, and tiny differences in the grind profile. That’s why your first step in calibrating a coffee grinder is to run a test shot of espresso, to see what you’re starting with.

Using 18 grams of coffee, and using the weighing scale to measure 38 grams of liquid espresso, time how long the shot takes. If it falls between 26-30 seconds, then the stars have aligned and you’re likely getting a tasty shot of espresso. See how the espresso is tasting, and feel free to adjust the grind size or recipe from there accordingly. If it’s lacking in flavour or sour, you may need to grind finer and extract a little more. Whereas if its thick, harsh, dry or bitter, you may want a coarser grind and shorter brew time.

If the test shot of espresso does not fall between 26-30 seconds, and it likely won’t on first attempt, you’ll need to adjust the grind size. Please note it’s vitally important to keep everything else consistent, meaning keep weighing out 18 grams of coffee and 38 grams of espresso every time.

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Why is My Espresso Brewing Too Quickly?

 If your shot of espresso is coming out far quicker than your target recipe, in this case 18g:38g in less than 26-30 seconds, and you’re making sure your puck prep is creating an even bed of coffee grounds, then the issue is likely your grind size.

If the espresso is brewing too quickly, your grind size is too coarse. This means that there is not enough surface area in the bed of coffee grounds to properly slow down the high-pressure water. You are likely underextracting your coffee in this scenario, leading to sour and weak flavours as you haven’t managed to extract all the good stuff from the grounds.

How to Fix a Fast Espresso Shot

The fix? Grind slightly finer to increase the surface area of your coffee, slow down the flow of water and increase extraction.

Make sure that after every change in grind size, you are purging a shot of coffee through the grinder and getting rid of this. A small amount of beans will be stuck inside the grinder at the previous grind setting, so you want to make sure you’ve gotten rid of this before testing the next grind size.

Why is my Espresso Too Slow?

 Conversely, if you’re shot of espresso is taking far longer than your coffee recipe, in this case aiming for 26-30 seconds, then you’ve probably ground too fine. The shot will likely be looking thick, dark and syrupy and tastes harsh, bitter and leaves a dry feeling on your palate.


Fixing a Slow Espresso Shot

If your shot of espresso is taking too long, you’ll need a coarser grind size. You want to reduce the surface area of the coffee and let the water flow through the espresso puck a little easier by going with a larger grind size.

Adjust your espresso grinder slightly coarser and make sure to purge a shot through the grinder before testing the new grind size. All else being equal, the shot should run quicker at this new larger grind size and reduce the amount of bitter and harsh compounds you’re extracting.