Equipment:
Expobar Brewtus II
Expobar bottomless portafilter
MACAP M4 Stepless Espresso Grinder
Digital scale accurate to 0.1g
Reg Barber Flat Tamper

Everything seems to be fine about brewing but I am unable to consistently get pinhole-less shots. Usually it's one or two annoying pinholes that do not affect the quality, volume or timing of the shot but they are there. It's driving me nuts! It really can't be that hard to get ride of these pin holes? Can it?

As you read through this post, I would love it if you could spot or suggest potential technique problems that could cause my pinhole leaks. Sorry no home video equipment.

I know the pinhole leaks indicate a tamping/distribution problem. That is, there is some small amount of channeling going on in my puck. And once in a while I will get a small (read small) leak around the edge of the basket that bridges over to the bottom edge of the PF holder. This shot usually has more than its share of pinholes as well. [I realize that this is probably due to an improper edge seal on the puck in that area in addition to some other channeling nearer the middle of the puck.]

I think I have everything setup as it should be. The new Macap stepless grinder (great) and the new Expobar bottomless portafilter as well as some good espresso blends. My favorite so far (although it may be a bit cliche) is the Intelligentsia Black Cat blend. I am a well within the 14 day limit. More like in the 3-9 day range.

I got my bottomless PF in about two weeks ago and from the get go was pulling good shots. Guess my dosing (15.0 g ± 0.2 g on a digital scale) and tamping is fairly close. I am consistently pulling 1.75 oz to 2.0 oz shots right around 23-28 seconds for a 15g dose (more often in the 1.75 oz range and 28 secs, sometimes even into the 1.5 oz range). Nice black drops all around to start (although it starts with a bit of a doughnut shape and then a full set of black drops). Then a good caramel stream with tiger striping (usually two or three merging into one stream). The tiger strips eventually thin and go away around 20 to 25 seconds. I assume blonding refers to when the tiger striping eventually stops. Although I guess that it is up to taste and user discretion exactly where to stop as there is no "exact point."

I have nice dark crema out the wazoo. It sometimes approaches ½ to ¾ the volume of the shot. I think the bottomless PF really helps here (and I suspect that the Black Cat may have a portion of HQ Robusta in the blend for crema).

But... no matter what I do I can't stop from getting a few pinhole leaks. They usually start around 15 seconds. I have tried about everything I can think of:

1) Half dosing the basket and evening out the grids, then dosing the rest of the basket and evening out the grids again before tamping. I focus on getting a bit more grounds around the edges for a good side seal.
2) Trying the Weiss Distribution technique (no improvement)
3) Using a nutating motion to get a better distribution/edge seal before a final tamp
4) Trying a finer grind and less tamping pressure (just seemed to screw everything up and I abandoned the experiment)

What I have found out so far:

1) Tapping the edge of the PF AFTER the final hard tamp to get the grounds off the sides of the basket (like David Schomer suggests) seems to worsen channeling problems. Difficulty here is that the grounds are tightly adhered to the side of the basket and require a strong tap to dislodge them. I think the tap is hard enough to at times disturb the puck.
2) I need to start my final hard tamp with the tamper level and keep it level through tamping. If the final hard tamp is not level, then re-tamping to level the puck seems to worsen channeling. I assume by cracking the puck. (Has anyone else had this experience?).

In general, I have the best (but not perfect) results from half dosing the basket, evening out the grids, then dosing the rest of the basket and evening out the grids again before tamping. I use an initial light nutating motion to make a final ground distribution and to improve edge seal, a light tap to dislodge grounds from the side of the PF, then I make sure the tamper is level and make a final 30-40 lb tamp.

What I haven't tried is just distributing the grounds as evenly as I can and then making one good 30 lb tamp in a single move--no nutation and no side tapping. I doubt this will help but I guess I need to try it tomorrow morning.

I guess the other option is to go back to a standard PF and not to worry about a few pinholes as they don't seem to significantly affect the quality of the shot.

-A

Hello,

Thank you for the detailed write up, it should make it easier for others to help. I'll try to help too if I can:

It sounds like you need to simplify things. Try your idea of dosing, leveling and level straight tamping with nothing else. I don't knock the basket at all (those stray grounds don't seem to hurt anything) and besides your taking a large risk for a very minor improvement (if any at all).

Another question I have is that I wonder what brew pressure your machine is running at, any way to tell? First though is to work on your technique.

Hang in there; sometimes these things just take practice.

My machine has a brew pressure gage.

Last time I checked, it was running right around 9 bar but it's been a while since I closely watched the gage. I will take a closer look tomorrow morning.

DCAD wrote:1) Tapping the edge of the PF AFTER the final hard tamp to get the grounds off the sides of the basket (like David Schomer suggests) seems to worsen channeling problems. Difficulty here is that the grounds are tightly adhered to the side of the basket and require a strong tap to dislodge them. I think the tap is hard enough to at times disturb the puck.
2) I need to start my final hard tamp with the tamper level and keep it level through tamping. If the final hard tamp is not level, then re-tamping to level the puck seems to worsen channeling. I assume by cracking the puck. (Has anyone else had this experience?).

I think tapping is unnecessary, but a gentle tap to the side or a tap down to the edge of the basket shouldn't be too detrimental.

If your tamp is not level and you've done a firm tamp, you really can't correct. You can knock it out and start over or if you do the WDT, you can break it up and use the grounds again. It is amazing to me how firmly locked the coffee puck is after a hard tamp.... when you re-WDT one you'll see.

You should try your straight down, no muss, no fuss tamp.... it should work as well.

I guess the other option is to go back to a standard PF and not to worry about a few pinholes as they don't seem to significantly affect the quality of the shot.

Sure enough, this is a valid approach. Give yourself some more time to establish consistency in your routine. I assume your are new to all of this? I bet that those pinholes will disappear after some more time.

For side channeling (and better results in general), I didn't want to believe it, but I do think convex tampers help.

TimEggers wrote:It sounds like you need to simplify things. Try your idea of dosing, leveling and level straight tamping with nothing else. I don't knock the basket at all (those stray grounds don't seem to hurt anything) and besides your taking a large risk for a very minor improvement (if any at all).

Another question I have is that I wonder what brew pressure your machine is running at, any way to tell? First though is to work on your technique.Hang in there; sometimes these things just take practice.

Tim raises a good point about pressure, the UK supplied Expobar Brewtus IIs are running at around 14 bar+! This does make things a little more challenging. Also when you pull a small amount of water from the group with the portafilter NOT loaded , does the water flash off to steam at all?.....im just wondering if the temperature and the offset are set correctly on your controller. The offset is the difference between the diplayed temperature and the actual temperature in the brew boiler. It's a long shot, but you never know, sometimes high temperatures can crater the puck a little.

If you decide you might adjust the OPV to bring your pressure down....2 things

1. On one expobar I checked the Gauge was 2 bar out, on another about 1 bar. It doesn't mean yours is, it's just worth bearing that in mind
2. If you have the OPV with the white nylon adjustment screw, it might not be a good idea to adjust it. See here

Again as Tim said, it could just be more practice....good luck

DCAD wrote:1) Tapping the edge of the PF AFTER the final hard tamp to get the grounds off the sides of the basket (like David Schomer suggests) seems to worsen channeling problems. Difficulty here is that the grounds are tightly adhered to the side of the basket and require a strong tap to dislodge them. I think the tap is hard enough to at times disturb the puck.
2) I need to start my final hard tamp with the tamper level and keep it level through tamping. If the final hard tamp is not level, then re-tamping to level the puck seems to worsen channeling. I assume by cracking the puck. (Has anyone else had this experience?).

Don't get too hung up on pinholes if the espresso itself tastes great.

From what I've read, after the hard tamp (~40 lbs), do a light tap on the PF. Do another hard tamp easing up to 20 lbs of pressure and do a finishing twist to give the grounds a good polish. Hopefully, that will help.

Good luck.

Hi,

My pinhole channeling went away :

(1) When I stopped tapping to remove loose grounds (unnecessary)
(2) When I started tapping the pf on the counter gently to settle the grounds after distributing but before tamping
(3) with practice

DCAD wrote:2) I need to start my final hard tamp with the tamper level and keep it level through tamping. If the final hard tamp is not level, then re-tamping to level the puck seems to worsen channeling. I assume by cracking the puck. (Has anyone else had this experience?).
-A

Yeah this was a problem I had for a while: I became obsessed with having a super-level puck, and so corrected after the hard tamp. All this did was break the seal between puck and basket and worsen channeling. If you're not happy, dump the puck, stir it up again and re-dose. Tamping with your elbow at 90 degrees on a non-slip surface helps keep it level.

Don't obsess over the puck being dead-level, it won't impact all that much on taste.

Just my experience

After reading some good articles on tamping, I tried using a slightly different method than when I started and it did help with any channeling for me. It was a two part tamp - dosing half the coffee, distribute, tamp lightly, then dose the rest and distribute, tamp, polish. If you tamp too hard on the bottom half you might choke the machine, but for me this worked great before I started using the WDT.

There was a point a little while back when I was almost about to give it all up. I was getting undrinkable results that were excessively harsh and bitter and not tasty at all. This was after an extensive modification to the machine including a pressure relief valve and gauge, PID, boiler insulation, etc. I figured I could control variables with little difficulty that I didn't have control over before. I wanted to blame the machine but like everyone kept preaching, it was user error. Not necessarily dosing/tamping, but I think it had a lot to do with the temperature. For some reason my instruments had failed me and no matter what the display temperature was constantly way below the actual temperature, causing everything to taste too hot and overextracted.
I hate to say it but when I switched to using my Mininova I got instantly better results. I think it's true that the E61 design is more forgiving than others in the sense that you can still make a good espresso with a relatively (!) wide margin of error.
Anyway, for your case, I would recommend taking a step back like I did and thinking about what is really significant. If you say you're getting tasty shots, what's the problem? So what if you get pinhole jets every now and then? I know you feel like you're not reaching the full potential of the coffee. But then you have people with Versalab M3's and double boiler digitally controlled LM GS3's that have been pulling shots for more than a decade who still aren't satisfied. There's really no other explanation other than the human desire to improve on a learned skill. It's the reason why we're here on these forums.

Excuse my existentialism but I've just been trying to put the whole espresso world into a broader perspective and stop looking at fussy details lately, and I think it's helping my shots taste better for some reason.

Given that you've tried the WDT already, based on personal experience, I would say:

1. Brew pressure too high
2. Brew temperature too high
3. Try a mildly convex tamper (like the RB US curve, which is what I use these days) I too was skeptical, but I do think a bit of convex helps.

The only other thing I'll add, is that, using the WDT has made all my extractions start uniformly across the basket, no donut shapes at all. This doesn't seem to concur with your experience, so it might be worth revisiting this. The first time I tried it in desperation I didn't think it helped, but, in the face of vast forum experience to the contrary, I tried again, and I've never really looked back. Or rather, it's helped me realise that I was doing absolutely everything else wrong It also made me realise that even the thwack-thwack of the doser lever on my Mazzer Mini was not breaking up the grounds as well as I expected, especially on 3-4 day old beans.

I'm still finding it an uphill struggle at times, but I think everyone does. I too was ready to jack it all in.

EDIT: I suppose I should have added my actual routine:

Grind and dose 16g into basket in portafilter, rotating to even things out
Stir grounds vigourously in the basket with a small pin, I don't use a funnel, with upto 16g I can contain the fluffed grounds in the basket
Slight tap on the bench or the grinder forks to settle and check the levels
Gently apply RB US curve tamper into basket, using finger ends to ensure top of tamper is levelling relative to the basket top
Single 30lb tamp, plus gentle twist to polish
Gentle blow to cleanup stray grounds