Whether you are a seasoned barista, a beginner setting up your very first espresso machine, or somewhere in between, you have likely had “channeling” when pulling a shot of espresso. This is most obvious when using a bottomless (or naked) portafilter, and is characterized by little jet streams that spray every which way. Channeling is frustrating and affects flavor by resulting in a very sour and/or bitter shot (not to mention the mess it leaves). Channeling is described by Daniel Harrington in the Espresso Coffee Guide as “…the undesirable effect of the espresso machine’s hot, pressurized water passing too rapidly through some parts of the puck – the roasted, ground coffee in the portafilter – while not passing sufficiently through other parts of the puck. When this occurs the shot will be under-extracted, and the stream coming out of the portafilter will show blond streaks.”
With that in mind, the question is how can channeling be avoided? We will go through the fundamentals of distribution and tamping and include a few tips and tricks.
1. Distribute the coffee grounds
We historically taught the Stockfleth method of coffee distribution. While it has been found to be very effective, it is also more difficult to master. As such, we have switched in our classes to the "tap technique". Don't quote us on the name, but that's what we call it. Give a few light taps on the side of the portafilter to ensure that there is an even bed of coffee throughout the portafilter. Once even, a quick tap on your tamping mat and you are ready to go.
2. Create a compressed puck
Tamping establishes a coffee bed that’s uniform and free of cracks and fissures. If you tamp well, the coffee bed puts up uniform resistance to the significant force of pressurized brewing water for an even extraction.
Hold your portafilter firm and level on the tamp mat or stand (it’s important that the portafilter basket is flat, and that you are not tamping at an angle). Grasp your tamper as if you are shaking hands with a doorknob, and apply light, even, and equal force to the coffee bed. Use the sides of your thumb and forefinger to gauge if the tamper is level with the basket’s rim. The amount of pressure is not nearly as important as your consistency and ability to keep the tamp perfectly level. Our friends at Barista Hustle conducted an interesting experiment to measure the difference between a comfortable tamp and a very heavy tamp and there was only a 3% difference. So remember - no need to be overly forceful – comfortable and firm are best.
Some baristas then polish the tamp by lightly spinning the tamper – a matter of style, not a necessity. Wipe away any grinds that have fallen on the ears of the portafilter and basket rim.
Give it a whirl and if you have questions give our team a call!