Tamping pressure

Beginner and pro baristas share tips and tricks.
verm.11

#1: Post by verm.11 »

Tamping pressure has always been linked back to the flow rate of the shot.

However, shots are being extracted under pressure ( up to 9 bar pressure). With such high pressure through our puck, does it really matter how hard or light we tamp?

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luca
Team HB

#2: Post by luca »

Maybe, but probably not by much.

It seems to have escaped pretty much everyone's attention, but this very question was examined in Cameron, Hendon et al's recent Matter paper:

https://www.cell.com/matter/fulltext/S2 ... -2#appsec1

If you go to figure S2 in the supplemental information, you'll see a nice graph of shot times vs tamping pressure, at 9 bar, 6 bar and at two different grind settings. The graphs are all pretty flat as the tamp pressure increases.

At the finest grind setting and 9 bar (however that was measured), there was the biggest change, being a 5 second faster extraction at 300N tamp pressure compared with 100N. But that was a change over 50s shot times, so those shots were basically choking because of the grind size anyway. Otherwise it looked like the biggest change might be a few seconds, and the direction of the change was inconsistent. No idea how good the data set for that graph was; maybe it was a bunch of n=1s. But at least it's some hard data, which makes it better than the waffle and urban legend that most people seem to base their coffee making decisions on.
LMWDP #034 | 2011: Q Grader Exam, Brewer's Cup #3, Australian Cup Tasting #1

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C-Antonio

#3: Post by C-Antonio »

I never bothered measuring tamp pressure but I can tell you that when I learned, ages ago, you were dosing, pressing up and off you went and pressing that way isnt the same that pressing down with an handheld separate tamper. Im sure that back then we werent pressing as hard as now but it was still enough. After decades I still dont know what my tamping pressure is (its so much an habit at this point)
Also everyone tamps at a different pressure and there is even people that believe you shouldnt tamp too much at all.
At the beginning, when water starts flowing on top of the puck and absorbing into it you dont have 9bar yet but then every machine is different on how gentle they get to pressure and its dialed grind settings are different, every grinder has its particular amount of fines that have to move so I wouldnt think there is a pressure that can be taken the same for everybody.
It becomes a range... with exceptions. Which makes it really matter only at the extremes.

Once you catch the right tamping technique that works for you the only thing is to just keep it the same for the sake of consistency, and when you get used to things you can decide when to tamp a bit lighter or heavier depending on the stuff you are working with, but for the most part if the coffe is distributed well and the tamping is enough to not have the water digging in on the surface and enough to give the puck a consistent "density"....
“Eh sì sì sì…sembra facile (fare un buon caffè)!”

jkapvt

#4: Post by jkapvt »

I'm fairly new but I've experimented some with tamping pressure. I've noticed as long as I firmly press I don't see much difference compared to when I really push on it. So, if this helps, pressing down kind of like the force to pump a bike tire right before it really starts resisting more air vs really pushing down doesn't make much difference I've noticed I've been using pressure more to fine tune. So if I target 18g and I end up with 18.5 I'll tamp lighter or if I end up with closer to 17.5 I'd tamp harder. But again I'm pretty new at this so keep that in mind.

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cannonfodder
Team HB

#5: Post by cannonfodder »

Tamping pressure is like chasing a white rabbit. People put way to much concern on it. The real key is good distribution in basket. The tamp simply levels the grinds, creates an even density across the entire puck for even extraction. As long as the tamp is consistent and level is all that matters be it a gorilla tamp or super light. I use 3 fingers of pressure. No more and no less.

The thing to remember is no amount of tamping will fix a bad distribution but a bad tamp can destroy a good distribution.
Dave Stephens

cgibsong002

#6: Post by cgibsong002 »

What would actually happen if you didn't tamp? Say, just wdt and tap to level? Would the pressure of the water still compress the grounds to create a puck? Would some of the top layer just blow apart?

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C-Antonio

#7: Post by C-Antonio » replying to cgibsong002 »

Why dont you try?

the effects can be different on different equipment... I had different behavior on the same machine using different grinders and different behavior with the same grinder on different machines but was done just out of curiosity (with friends we tried to see how fine we would go without tamping) the results really didnt justify going into a lot of trouble with it, so its not something we spent a lot of time on.
On machines regulated to the usual 8,5-9,5 range, specially if the ramp up to pressure is relatively slow, always tapping the portafilter onto the mat to collapse the coffee but no tamping, the puck actually remained intact with a shot running fast but not a gusher and it can be somewhat surprisingly drinkable-ish (with some beans, for sure I had worse stuff in some *$ ) not much body. What I saw is the surface of the puck looking pockmarked but part of that can happen when the water gets discharged by the 3way. On a Silvia regulated high the top of the puck wasnt in great shape but even there it seemed disturbed to about half depth or so
I think that, when it comes to the grinders, I explain the difference I had by thinking that one that creates a lot of fines would help that particular situation a bit better than one that is rather consistent.
All in all collapsing the grinds did some work but at least a bit of dressing the puck with a tamper should be given.

BTW a single try with grinds from a manual grinder that gave clumps, no distribution whatsoever, no collapsing of the grinds gave basically dirty water...
“Eh sì sì sì…sembra facile (fare un buon caffè)!”