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, at least most of the time? We will go through the fundamentals of leveling and tamping and add in few tips and tricks taken from our very own Craft of Espresso book.
First, level the coffee grounds.
The goal is to make the coffee bed level and flush with the basket’s rim. Hold the portafilter firmly on a flat surface and use a straightened forefinger to push the mounded coffee toward one edge of the basket (think of leveling off a cup of flour, except that you are not pushing the mound off the edge). Allow some part of the rise to remain, a decreased hill, but still a hill, near the edge of the basket. Repeat this motion in four directions – away from you, toward you, to the left, and to the right. After each pass, the mound is smaller. After the final pass, any remaining coffee can be pushed off the edge. Be sure that where coffee and basket meet, you have left no gaps. [Note – if you are single dosing, you will not have excess coffee grounds, but you may still level the coffee grounds using the same technique and make sure that the coffee grounds come all the way to edge, all the way around].
Now tamp it.
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. You need not be overly forceful – comfortable and firm is best. Some baristas then polish the tamp by lightly spinning the tamper – a matter of style not 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!
See Dialing In your new espresso grinder for more on the two methods of dosing.
Sources to read more: