By the time you see channeling, it's too late.

If you're regularly seeing channeling, it is likely that you're getting channeling at lower levels much more often. Check if you're under- or over-dosing the basket for your machine and coffee, if your extraction pressure is set too high, if your beans are low quality or very stale, and the quality of your grinder. If you find it isn't one of those things, then it is probably your prep.

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PIXIllate wrote:In my experience the use of a flow control to mitigate POTENTIAL channels is mainly about the phase in which you use it.

If you use a pressure hold around 2-3bar/zero flow stage at the beginning of the shot then the puck does seem to have an opportunity to saturate and swell which can ameliorate potential weak spots in the bed BEFORE they become channels.

Once you are at full pressure and the water is flowing through a channel there is most likely little to be done except minimize the mess.

Jeff wrote:If you're regularly seeing channeling, it is likely that you're getting channeling at lower levels much more often. Check if you're under- or over-dosing the basket for your machine and coffee, if your extraction pressure is set too high, if your beans are low quality or very stale, and the quality of your grinder. If you find it isn't one of those things, then it is probably your prep.

thanks a bunch, I'm finding these especially helpful...

PIX - With an E61 machine, can't you get that 2-3bar/zero flow stage by partially raising the lever (open flow without engaging pump), and give that an extended pre-infusion to achieve the same end?

Jeff - one of the mistakes I made with my first machine was keeping the pressure set on the high side, exacerbating other problems that might have been going on and giving me more channeling...I've been reacting to that realization by seeing flow control as a potential way of keeping things on the tame side (which may or may not make a big difference, esp. if everything else is spot on)...

Appreciate the conversation...

If your machine is plumbed in and you have your line pressure set to 2-3 bar then yes, kind of.

If your using the tank then no, not at all.

Here's the technique I developed to give me maximum control and response time. You can easily modify the soak time to suit different roast levels ranging from filter roasts with a 20-30 second zero flow/soak to a darker espresso roast where you might skip that phase altogether as the bed holds together much better.

An Even MORE Considered Approach to E61 Flow Control (now with video)

If your machine is plumbed in and you have your line pressure set to 2-3 bar then yes, kind of. If your using the tank then no, not at all.

Actually, one can presoak/infuse at any given pressure on a reservoir machine. I have done it for years. Simply raise the lever far enough to engage the pump, then lower it to the mid-position. It helps to have a manometer on the e61 group head, but on my HX, which used the hole for a thermometer, through experimentation, I found that about 5-seconds of pump would yield about two bar of pressure YMMV. You don't want to go too long, else the e61 preinfusion spring causes a rapid rise...that's at about 4-bar. It's kind of mesmerizing to watch it on the manometer. The pressure rises above the target level, then when the lever is moved to the mid-position, the pressure will gradually drop as air is expelled from the puck. Once the air is gone, the puck swells and the pressure stops dropping. Get your timing right, and you can make it sit there at one or two bar for quite a long time. Eventually, a few drops of coffee will begin to emerge. I've played with insanely long infusion times, but find that 10 or 15 seconds is about the longest I like, or odd flavours occur in the cup.

Nunas wrote:I found that about 5-seconds of pump would yield about two bar of pressure YMMV.

this depends on basket shape and gap between screen and puck.
bigger screen to puck gap= longer to build pressure.
slower pressure ramp = longer. (rotary is very fast here)
lower temp = longer.

interestingly enough, this doesnt necessarily correlates to puck saturation.
with small gap, water soaks into puck while its building pressure. despite fast pressure ramp, more puck is saturated together with the pressure buildup.

with more gaps, the puck will be compressed more by the pressure and build resistance first instead of saturating, hence most of upper puck will be extracted, leaving bottom puck less extracted.
doing a slow ramp may help this, but too long ramp and preinfusion you may have shots running before it hits max pressure.

note that contradictingly, lower pressure requires finer grind, because puck compress less and allow water to pass thru faster. preinfusion is a low pressure flow, and longer preinfusion results in shorter brew time due to fast flow.
of course u can grind finer to prevent this, but then u'll need to be more meticulous with puck prep to avoid channeling and maybe also hit the issue of upper puck extraction.

end of the day its still a balancing act, and still require learning consistent good puck prep. but then u'd have one more item to balance (unless this can be automated).

My best pours, consistently come with preinfusion followed by peak extraction pressure (usually 9 bar or slightly under), and then flow control at level or less flow. I'm a believer that flow control helps prevent channeling and provides, when used appropriately, the best shots.