Since I have been a barista, I have followed the method of loading the portafilter, evenly distribute and swipe back into the dosing chamber, light leveling tamp with the tamper then (here is the part in question) a light, easy knock on the cleat of the portafilter with the handle of the tamper to settle the espresso off of the sides of the basket, followed by a harder polishing tamp before loading into the group.
Even if I deliberately try not to do the "tap" it is just muscle memory reflex and I do it anyway. Pros, cons, good, bad??? Whats the deal, please post your position.
Don't tap, for reasons stated above.
Don't worry though, it'll probably only take you two shifts or less to get rid of the "muscle memory" part.
Recently I changed where I work and at this time I also stopped tapping. Took a bit of getting used to but now that I did I am happy with the results. Agree with most of what was said above.
This is why I like it when people have and train with bottomless portafilters. It moves the dialogue from talking about what should happen to talking about what does happen. Observations > claims.
Buy and train using a bottomless portafilter. If you notice problems with your extractions, change what you do until they go away.
Todd Campbell said:
Had this conversation with a barista at a shop in town last night. Couldn't get him to change his mind on tapping. He claimed a follow-up tamp should clear out the channeling. Not really buying that.
.::I have wondered this same thing. If tapping before a tamp does not induce channeling, why would tapping after the tamp induce channeling if you tamp again? My observation is that channeling does occur more often when you tamp, tap then tamp again. So my only guess would be that when you tap before tamping it settles and distributes... to a certain degree... because the grounds are loose. If you tap after a tamp, the coffee puck cracks and pushing down does nothing to right that wrong. It is like cutting something in half and then smashing it... Does that make sense? That is my guess.
I think you just have to try different things in order to know what works and what doesn't::.
Paul Yates said:
What about the settling taps on the forks of the grinder? Wouldn't that also encourage channeling? It seems the popular method these days is to grind, tap on the forks, grind a bit more, then tamp with no distribution. Seems like channeling would be likely?
The direction of motion in a carefully-executed settling thump is vertical. The ground coffee particles' inertia should force them downward, filling in voids and perhaps affecting size-distribution of the particles.
The direction of the force that results from a tamper tap is from the side. If done carefully, it can break loose that rim of grounds. If done with too much energy, it can kick the puck to one side or crack it. Since the tamper force is downward, it may not be able to force the puck back against the basket wall.
If you're looking for a comparison, it seems like the side tap would be more like whacking the portafilter up into the bottom of the doser than dropping it down into the forks...
The biggest difference, though, is that the settling thump works to improve shot consistency and quality while the side tap doesn't. We can speculate about why that is, but that is really the bottom line.
I've always explained it like this:
If you really wanted to ruin the sidewall seal of the puck, and you wanted to ensure a bad extraction while still focusing on proper distribution, how would you do it?
The inevitable answer is to tap on the side of the portafilter. The next question I always ask is, "Then why do it?"
The usual response has something to do with the human's OCD about whatever remnant grounds are left clinging to the upper side walls of the filterbasket. The fact of the matter is that the initial water contact breaks grounds loose from the surface of the puck anyway, and while these things may make keeping the equipment spotless only slightly easier, the coffee (in the cup) doesn't care either way. The coffee cares more about even resistance for an even extraction than whether or not the filterbasket "looks" right.