The Perfect Espresso
When it comes to achieving the perfect extraction of your espresso you need to know your variables.
What is considered a perfect extraction first of all?
A perfect extraction is a 25-30ml shot of liquid gold extracted from one side of a double spout group handle in one continuous extraction between a time of 25-30 seconds (Australian Industry Standard).
To achieve this consistently you have to understand the following 3 variables and how to best control them.
• Distribution and Tamp
• Grind Size
A standard “double” size basket will fit around 18-19gr of coffee, but you will need to check this first. When it comes to dosing our coffee it’s important that this doesn’t change, or our extraction time will change inevitably changing our flavour profile. By using scales and weighing out our coffee, we can ensure our dose is always consistent. Even up to half a gram can change your flavour profile.
Distribution and Tamp
Coffee distribution is how your coffee is distributed (how it sits) once dosed into your filter basket before tamping. With a poor distribution the chances are much higher for channelling to occur (when water from the group head finds a quick path through your coffee) resulting in an uneven extraction. To distribute your coffee before tamping you can use a distribution tool or simply tamp your group handle on the bench or a tamp mat making the coffee settle evenly, removing any air pockets that create the weak spots for channelling. The way you tamp is the next variable you can control. The industry has introduced tools that allow you to be consistent with the amount of pressure you apply to the coffee every single time (30lbs). If we begin to fluctuate in pressure this too will affect the extraction time and flavour profile of your coffee. We also need to be consistent in applying a level tamp to the coffee, again to prevent channelling and to promote an even extraction.
The grind size is something as a barista we need to understand the most. This is the one variable that is the hardest control. Environmental factors such as; heat, light, air and moisture will affect how the coffee is ground along with a number of other variable ranging from the age of the coffee you're using to how much coffee is in your grinder hopper.
Firstly, let’s understand how coffee that is too fine or too course affects your extraction rate. If our coffee is too course the water is unable to slow down long enough to pass through the coffee extracting out the rich flavours giving us a watery or sour taste. The finer the grind the longer it takes the water to pass through giving you a bitter or burnt taste. I like to think of water passing though rocks and sand. The sand will always slow the flow down. This is where the skill of the barista comes in and is able to adjust the burrs in the grinder to keep a consistent grind size. In turn, allowing the water from the group head to pass through your 18-19 grams of coffee, distributed correctly, and tamped evenly and at exactly 30lbs of pressure to achieve a perfect espresso - 25 - 30mls of espresso in 25 to 30 seconds.