Achieve better espresso by mastering even coffee distribution and level tamping—consistency matters more than pressure.
- Channeling causes sour, bitter espresso when water flows unevenly through the coffee puck
- Even distribution matters more than tamping pressure—use tap technique or distribution tools like the Wedge
- Tamp consistently and level (not forcefully)—experiments show only 3% difference between light and heavy tamps
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 can affect flavor, 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, starting with the video below.
1. Distribute the coffee grounds
By tamping firmly and flat, we can ensure the whole puck is evenly extracted. 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 to the "tap technique" in our classes. Don't quote us on the name, but that's what we call it. Give the portafilter a few light taps to ensure an even bed of coffee throughout. Once, even a quick tap on your tamping mat and you are ready to go.
Even better, use a distribution tool like the Wedge from Saint Anthony. By giving this a couple of spins, you can ensure that the grounds are spread super evenly before tamping.
2. Create a compressed, level puck
Tamping establishes a coffee bed that’s uniform and free of cracks and fissures. If you tamp well, the coffee bed offers uniform resistance to the high pressure of the brewing water, ensuring 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 one, and found only a 3% difference. And as you saw in the video above, we pulled 5 shots with different tamps at forces ranging from 40lbs to 5lbs, and the shots all pulled about the same, with our yield and shot time very close together. So remember - no need to be overly forceful – comfortable and firm are best.
You can also use tools like the Saint Anthony Industries Levy, which we love here at Clive. The collar makes sure your tamp is level every time. Check out all our tampers if you're in the market, including our own wood tampers made right here in Portland.
Some baristas then polish the tamper by lightly spinning it—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!