This morning, in my sleep-addled haze, I dosed my double basket, smoothed off the coffee as usual (N-S-E-W), then for some reason I locked it straight into the macine without tamping.

What was unexpected was the result, which was it choked the machine, the spout was dripping very slowly.

I dumped the lot, dosed the same and tamped hard. This gave me my usual 30-second pour.

I normally tamp quite hard, but this is making me wonder if I am missing something. Was it because the grounds, although loose, were pushed against the shower screen?

I am half-tempted to play with using the tamper very lightly to give some headroom, but no more. Given the choking I got this morning, I may need to go coarser on the grind.

Thoughts?

probably because the grounds were loose, they absorbed water easily and all swelled instantly, that may be the reason why your machine choked (ie. pourover coffee)

Could be as you suspect you did what I think is called a showerscreen tamp that compressed the grinds a bit but left no headspace. What kind of machine do you have? Is it preinfusing? Is your roast pretty fresh?

I'd guess the blooming grinds without any headspace for expansion locked into the pf and offered enough water pressure resistance to choke your machine.

Interesting, though. The advice I've heard often enough for channeling problems was coarsen the grind and/or lighten the tamp which seems counter-intuitive. It wouldn't work if your technique is right on, I assume, but if it's your technique that's the cause of channeling fast pours not your grind size then indeed coarsening up or lightening your tamp would be the way to go. Bad technique with too fine of a grind or too hard of a tamp encourages channeling, I find.

I've often wondered if I'm really grinding too fine or tamping too hard and just getting controlled channeling extractions more than good, even ones. More than once I've choked a machine with same grind and same tamp and it led me to wonder if maybe at those times my technique was on and that's why the machine choked.

The machine is a cleaned-up used Rancilio Epoca, HX with a vibe pump and tank. It doesn't pre-infuse, but it does go a good 6-7 seconds from pump-on before you can hear the pump quieten from the pressure build-up and coffee start to appear on a normal extraction. The beans are about 4 days from roasting, and are no where near darkly roasted.

I hadn't considered that what I thought was a good pour was actually a choke with a bit of chanelling all adding up to a 25 second extraction. I think I need to try and replicate all this with my naked portafilter, but I think I will need a good few more beans first!

darrensandford wrote:This morning, in my sleep-addled haze, I dosed my double basket, smoothed off the coffee as usual (N-S-E-W), then for some reason I locked it straight into the macine without tamping.

A few years ago, during an early, sleep-fogged prep, I was refilling Silvia's reservoir and nearly poured the water into Rocky's bean hopper!

I've been meaning to make a post about a similar tamp vs. no tamp surprise. I was curious about the effects of preinfusion, and after playing around a bit pulling shots ended up dosing, leveling and tamping, but instead of locking in, and pulling a shot, just pouring a couple onces of water in to the portafilter - just to get an idea of what was happening. I then dug around in the wet grounds with a toothpick to see how deep the water penetrated and if it soaked in evenly or not. I then did the same thing, but without tamping, just dosing and leveling.

The surprising result was that the water in the tamped shot soaked through noticeably further then the untamped, the opposite of what I was expecting. The tamped grinds were wet about 1/2 way through, maybe more, and the untamped grinds were always less then 1/2 way soaked through. I tried it out a couple times, keeping the dose and grind consistent, and got the same results.

A few theories on what was happening:

1. It was just a freak occurance.
2. The tamp 'locked in' some bad distribution and allowed water to seep down through little channels
3. The tamp 'locked in' the distribution of the fines in the puck, while the fines in the untamped pucked all got funneled down and clogged up any passages through the grinds.

After inspecting the grinds from my grinder (Gaggia MDF) I'm guessing that option 3 is most likely. After sifting a dose of ground coffee it was clear that there were a decent amount of fines. Now I'm wondering if this could be one of the advantages of conical grinders, if the way that they initially shear the beans down to grinding size may prevent the creation of a lot of fines, and that gives you a more consistent puck, and shot.

TrlstanC wrote:The surprising result was that the water in the tamped shot soaked through noticeably further then the untamped, the opposite of what I was expecting. The tamped grinds were wet about 1/2 way through, maybe more, and the untamped grinds were always less then 1/2 way soaked through. I tried it out a couple times, keeping the dose and grind consistent, and got the same results.

Thinking about it, untamped coffee probably has a lot of air between the particles, meaning that there is less contact between the grains of coffee. I think that this would give the pre-infusion unpressurised water a harder time, as the water would have to overcome surface tension to pass from one particle to another across an air gap, but would soak easily between touching particle, meaning that the water would soak through a tamped puck more quickly.

...maybe.

Randy G. wrote:A few years ago, during an early, sleep-fogged prep, I was refilling Silvia's reservoir and nearly poured the water into Rocky's bean hopper!

Eep! Not the way to start the day!

darrensandford wrote:The machine is a cleaned-up used Rancilio Epoca, HX with a vibe pump and tank. It doesn't pre-infuse, but it does go a good 6-7 seconds from pump-on before you can hear the pump quieten from the pressure build-up and coffee start to appear on a normal extraction. The beans are about 4 days from roasting, and are no where near darkly roasted.

I hadn't considered that what I thought was a good pour was actually a choke with a bit of chanelling all adding up to a 25 second extraction. I think I need to try and replicate all this with my naked portafilter, but I think I will need a good few more beans first!

Diagnosing extraction and playing with variables I find hooked me on espresso and makes it really fun.

I don't know the design of the Epoca but I wouldn't be surprised if it has a solenoid to control preinfusion. 6-7 sec is about what I get with what I believe is the lever actuated preinfusion of the Vetrano I've got.

As far as too fine and controlled 25 sec choke I've wondered about that when looking at my pucks after extraction. Even stopped before any naked pf squirting or significant blonding I find signs of channeling, mostly holes near the center of the puck. When I don't see holes is when a once in a blue moon shot chokes with no flow or the extraction tends to a deep charactered ristretto where it once was an average tasting normale.

Could be a it's a God Shot factor where God Shot is just variables that need to be tweaked more precisely come together every once in a while by chance. Something to have fun with for sure.

Randy G. wrote:A few years ago, during an early, sleep-fogged prep, I was refilling Silvia's reservoir and nearly poured the water into Rocky's bean hopper!

I was cleaning the grouphead with a wet toothbrush, and then sleepily poked the same dirty, wet thing up the clean, dry spout of my grinder. Swearing and scrubbing ensued.