I'm not sure what the technical term for this is, or if there even a technical term, but I find that a lot of baristas seem to skip this step. They go right from the grind to the tamp. To me this would seem to cause a lot of poor extractions. When it's not even, part of the "puck" is going to end up denser than others, and the the water under pressure is going to force its way through the less dense portion creating a over-extraction on part of it and an under-extraction on another part. If you examine the puck afterwards you'll see that parts of it are damper than others. If there is another way to look at this I'm not sure what it is.
Hey, Zev. That's what we call settling and distribution. The idea is to create as even a bed of coffee as possible, as water will always find the path of least resistance, which is what leads to the uneven extraction you mention. Another big issue around this is hitting the portafilter with the tamper, which can create cracks in the coffee bed. The type of grinder is also going to influence this, as doser vs. doserless are going to provide wildly different beds of coffee if you're not doing some kind of distribution.
I'm all for a repeatable, consistent way to distribute, so I keep my finger as straight as possible and sweep across the coffee and back, and then across once more (makes for three passes of the coffee). However, we'll be doing some experiments with the Saint Anthony Industries Shot Collar and Levy Tamp in the school in the next month or so, so I may have things to say about that.
What's your solution to this problem? I'd love to hear your thoughts.
the finger method sounds like the best option, and there's no food safety issue since the heat is going to be applied afterwards. At one point we were using a a flat piece of plastic (shaped like a ruler) for the distribution, but I think the "old fashioned" method is still the best in this case. I'm just wondering why so many baristas I come across insist on not doing it at all. Perhaps they lose some grinds over the side?
I hear you, Zev.
As Jen noted, distribution is important. Probably more important than how you tamp.