Distribution Techniques for Making Espresso
Let's talk about some methods for distributing the coffee grinds in the portafilter basket to bring out a perfect espresso.
What is Espresso Channeling?
If you make espresso at home or in a cafe with a bottomless portafilter, there's a good chance you've seen a jet of spray paint the shiny chrome drip tray or face of the machine. That's called channeling.
Extraction & Consistency
Channeling occurs when water bypasses the middle of the puck of espresso and shoots down the edge of the basket during extraction. This isn't ideal because that means that your overall extraction wasn't even. There are many techniques and tools you can use to keep your puck prep (the grinding and tamping phase) consistent, and therefore keep your extraction consistent as well.
One great tool you can use is a “Precision Tamper”, or a tamper that more accurately fits your portafilter/basket. We'll talk in the context of a standard 58mm grouphead, but you can apply this to any size. Most tampers are made to a spec of 58mm wide. Makes sense right? But actually, your basket is probably closer to 58.5mm or even 59mm wide, so you have about 0.5mm of un-compacted coffee around the outside edge. You might've seen this in the form of a thin wall of coffee sticking up above the surface after tamping. That is the perfect environment for channeling to occur. So one of the easiest things you can do that doesn't require a change to your process in the morning is buy a 58.35mm or 58.5mm tamper. This should evenly tamp ALL your coffee, and reduce the possibility of channeling.
How do you Distribute?
The other technique you can use is called distribution. Now there are a few different ways to distribute your coffee, and we'll explain the pros and cons of each and how it affects your brew.
Weiss Distribution Method
The first one is going to be via the Weiss distribution method. This involves using a thin metal rod, such as a paper clip or needle, to stir the coffee grounds. One of the main advantages is clumping at the bottom of the basket is also broken up, as opposed to just the top. This can be an extremely valuable technique, especially for those using entry-level grinders with a tendency to clump. Even with an extremely high-end grinder, proper WDT Techniques can be seen to improve flavour and consistency. Typically you'll see a slower shot, as a side effect of reduced channeling, so it's important to either use the Technique every time or not at all, as it could throw off your dialing-in process.
The other major tool for distribution is the standard Distributor/Leveller. These are typically finned, and once put atop the portafilter, they smooth the coffee out at a specific level. This can be quite helpful for increasing tamping consistency, as your tamping pressure is more evenly applied. This does not, however, distribute clumps on the bottom of the basket. If your grinder at home is prone to clumping, one of the other two distribution methods may serve you better.
Finally, a lesser-used but very effective method of distribution is called shaking. This is the process with which you grind into a dosing cup, or even better, a purpose-made tool like the Webber Blind Shaker, and shake the coffee grounds before dosing into your portafilter. While you might be worried about fines migration or granule convection, an article by Barista Hustle looking at several studies proved there's not really a discernible effect on taste whether the fines are on the bottom or top of the puck before extraction.
Now armed with that info, you can go forth and right any extracting wrongs you may be committing. Of course, as is always the case, a better grinder, with larger burrs, promotes better grind uniformity. This is the single most important variable in good-tasting espresso.