HOW I ELIMINATED channeling.
1-This is JUST my experience on my equipment but it might help. I chose to experiment with ideas I heard of no matter what science says should or shouldn't happen in a puck. It's results that count. I only make 2 espresso's a day for myself unless we have guests. (And that won't happen untill covid19 lockdown ends)
- Mazzer super jolly custom modified for single dose.
- 1980's LaPavoni pub single group commercial machine (the volumetric model with large boiler and external pump.)
- Naked portafilter.
- IMs shower MA200NT
- IMS basket E&B B702TFH26 - 18-20g
3- Recipe. in this day of 2+:1 recipes with larger yields I'm a bit old school and go for the thick syrupy espresso. No milk ever. So it's currently 19.5 dose 28 yield in 28 seconds. I have found using a dose on the higher end of the baskets recommendation where the grounds just touch the shower actually gets the BETTER pour with less channeling. Obviously I can't see exactly what goes on in the portafilter during extraction but I see faint marks of the shower sometimes and always see a mark from the shower screw.
4-PROCESS: this seems long winded. I only make 2 a day so I don't care. It works for me. All these steps get me the best pour without channeling and the best espresso in cup to my taste.
A- fresh beans. You'll work out when the best period for your roaster is but for me curently it's between 2-9 days from roast. If your roaster won't date the roast go elsewhere.
B- I weigh the beans into a dosing cup as I don't want to waste. I spray the beans with a tiny amount of water with a small spray bottle to eliminate static (RDT). When doing this I see the grounds flying out of the grinder, loose compared to a little clumpier when I don't.
C- Grind. I won't go into dialing here but the jolly is a reasonable flat burr and I've done some modifications to enable less retention of old grinds and better grinding of a single dose without a hopper. I can put in 20g beans, get 19.5 grounds and flush out 0.5g grounds consistently.
D- I grind into a dosing cup. I've found for whatever reason, even with WDT it seems to be better with this intermediate step.
E- Weigh and adjust dose here. I POUR the grinds into the portafilter and find how I do this doesnt matter. However if I try to upend the dosing cup on the portafilter upside down and rotate as described here http://www.youtube.com/watch?v=C9u9S_-PcwQ
I get bad results. It seems to be something to do with the density of grounds at the bottom of the puck compared to the bottom. I'd love this shaking technique to work for me.
F- Hand tap to level the grounds. I use a dosing ring
G- WDT. I use a paperclip straightened out. I know what they say about scratching the basket etc but a toothpick leaves large hollows in the puck..at least for me
H- Tap the bottom of the portafilter on the bench. I find how this step is done, makes a big difference to the pour. If too hard you can feel when tamping that the top is soft and the bottom dense. Also after tamping sometimes the level grounds go unlevel. If this happens I scrape some grounds around a bit on top with the paperclip, otherwise the pour is uneven.
I- I use a wedge style grooming tool. I don't believe these tools really distribute well especially low down but they do give a great level puck to make level tamping easy with a regular tamper.
J- Tamping. I find with all this prep to this stage it's really easy to get the pressure right. You can feel easily when the compacting stops.
K- Pre infusion? My machine does not have pre infusion. I've been following the development of the decent espresso machine and on John's blog (one of the decent founders) he mentioned their staff have a competition for the best pour each day and someone sprayd the puck with cold water with excellent results and showed the difference in the spread of water hitting a pre wet puck vs a dry puck. I tried this and it was a game changer. I use the same sprayer I use for RDT. I hold the portafilter about 200mm away and move it about (to get even coverage) while I give it about 6 pumps on the sprayer. I've tried different amounts and this seems right for my sprayer and grounds. It's not a lot of water at all and it's a fine mist.. After trying and using all the other techniques this made the BIGGEST DIFFERENCE to the pour and channeling than anything!!!!!! While I do this I'm flushing the group
L-Make sure you don't slam the portafilter into the group as I've found this can unseat the puck in the basket.
M- Even though my machine is volumetric I'm always starting and stopping the pour with the manual button my machine has. I'm weighing and timing the pour.
OMG that seems like a lot of steps when separated out and written down but every time I remove a step the espresso is not as good. It has to be as good as the best cafe/barista I know can make it.