About channeling, Do you see a difference when you use light or heavy tamps?

I do.

Since a few days, I have grind finer and use just little tamp pressure and experience less channeling.

How about barista pressing just a little on the tamper, are you experiencing less channeling?

I conquered channeling by tapping the basket after final distribution.

As far as light vs hard tamp I haven't noticed a difference (as long as the grind change is correct to compensate for the change in tamp pressure).

Tamp pressure is not a reason channeling occurs. Channeling is an a symptom of uneven flow through the puck, resulting in a less-than desirable cup. Whether you increase or decrease your tamp pressure doesn't fix the channels.. The reason you see less channeling is that the less restrictive flow may actually be hiding the uneven flow.

With my gaggia classic I saw a lot of channeling, Using an open PF (coffee stains everywhere from the gushers) I think saw a trend to most channeling with pre ground coffee (illy etc), less so with better stuff ground on a decent grinder in the coffeeshop but still a fair amount.
Since i'm using a mazzer SJ there is hardly any channeling anymore (recalling one small sprotzer at one point), in the period I was tinkering with the Faemina I did use the gaggia classic and was surprised how even the flow was ( and how nice the espresso came out of the filterbasket with tiger stripes and all that)...it also rekindled the search for a naked PF as I'd like to watch the flow on the Faemina every now and then.

By 2cts would be that the grinder has most impact on channeling, I used to do the WDT as I had to but I somehow expect I could skip it with my current setup.

The woulds best tamp will not fix a bad distribution, but a bad tamp will ruin a perfect distribution. Personally, I light tamp. Only 2 finger on the tamper, probably in the 15 pound range.

I suspect having a K10 makes it easier to do a light tamp.

Ditto Dave's tamp of 15 pounds. Occasionally go back to scales to insure 15 pound tamp. Haven't had channeling in years. Using either Vario or Pharos.
One mitigating factor in channeling is those that have 58mm portafilters.

Since my Cremina is 49 and La Spaz 53 they are not as likely to channel. The La Spaz double is really heaped at 16.5 grams and the Cremina at 14.5 prior to lightly tapping, leveling and tamping.
In leveling I like to retain half a finger above rim.

Might add all this is with roasts that are usually gone by day 10 or 11. By day 10 have had to tighten the grinder up noticeably.

weebit_nutty wrote:Tamp pressure is not a reason channeling occurs. Channeling is a symptom of uneven flow through the puck, resulting in a less-than desirable cup. Whether you increase or decrease your tamp pressure doesn't fix the channels.

Channeling -> Over extraction. Channeling results from poor distribution and "consolidation" (which includes inter alia even tamp pressure, a level puck surface, and a good seal of puck to basket all the way around the edge).

I think it's possible for preinfusion to homogenize and "glue" together a loose puck that's sufficiently coherent that it doesn't channel; but might have if not for preinfusion. In that sense, a soft tamp might allow the grinds to move around enough for preinfusion to homogenize the puck. Then, hypothetically, a soft tamp might make a positive difference.

The reason you see less channeling is that the less restrictive flow may actually be hiding the uneven flow.

• A. No; and
  B. It's a statement which makes no sense whatsoever if for no other reason than it's self-contradictory.

Unless the puck is made solid by tamp pressure so high that pump pressure isn't enough for the water to penetrate the puck; or the puck is so loose as a result of no tamp that, in an absence of effective preinfusion,* it morphs into a loose suspension during the initial rush of water, tamp pressure doesn't effect more than the first couple of seconds of flow. Grind size and water pressure mean a lot more to flow rate.

cannonfodder wrote:The woulds best tamp will not fix a bad distribution, but a bad tamp will ruin a perfect distribution. Personally, I light tamp. Only 2 finger on the tamper, probably in the 15 pound range.

+1. I'm also probably in the 15lb range with my heavy, conventional Hai Pham tampers with nutating and leveling. Lighter though -- maybe 5lbs -- with my Butterfly which is a very light disk, with no handle.

At the risk of repetition, grinder, grind size, distribution, consolidation and preinfusion are a lot more important than tamp pressure.

Rich

*Nuova Simonelli "SIS" preinfusion is famously good enough that an okay shot can be pulled without any tamping.