A past thread(s) on backflushing, cleaning, and maintenance of the E-61 motivated me to do an impromptu, unscientific test. I went about two months without a chemical backflush. During that time, at the end of each session, I flushed until no coffee showed in the stream (to clean the screen), then used the stream to wash the portafilter and basket. I then locked in the blind PF, did a wiggle to clean the gasket and upper areas of the group, and then did two, full-pressure, clear-water backflushes. Once or twice every two weeks I ran a towel around the gasket groove, but no other cleaning was done to the group. At the end of that time I removed the screen, gasket, and dispersion disc and found them to be exceptionally clean. A wipe of the grouphead under the screen showed almost no coffee residue there and even the inside of the screen itself was very clean.

My motivation behind this was that using detergent on an E-61 removes any lubricating film and causes excess friction where the cam moves the brew and infusion valves. That continues until oils build up there to act as a lubricant. In another couple of months (to give it an extended test period) I will disassemble the group and remove all the valves to examine all parts to test the effectiveness of this level (or lack thereof) of maintenance.

Very interesting. Thanks for posting this.

So how many shots per day are you pulling? I pull around four or five shots a day, so going two months would be around 240 - 300 shots before chemical cleaning. I think most sellers recommend chemical backflushing every 50 shots or so, so your experiment is well outside the recommended regimen. But it's possible that there's no real advantage to frequent chemical cleanings, unless you're running a shop and pulling dozens of shots a day.

interesting experiment Randy. Here's my one data point:

On my VBM DB Jr, after 2 shots each morning, I also ran the group to brush the screen, wipe the group
and one clear water backflush afterward. I'd do a chemical backflush every 2-3 weeks and
the water that comes out of the drain spout is nasty every time. Perhaps 2 does the trick...

I think that when I pull the group apart next time I will have more specific info. I will want to find out if the coffee crud (as you are seeing being rinsed out) is in the infusion chamber or in the exhaust valve area. I will separate and wash those parts separately to see.

If you don't mind replacing the cam and the two valves occasionally (or theoretically, somewhat more often) , then chemical backflushing is nothing to worry about in terms of machine life.

Function and taste of coffee will then be discussed after I do the cleaning experiment. Probably the end of February.

Randy G. wrote:... At the end of that time I removed the screen, gasket, and dispersion disc and found them to be exceptionally clean. A wipe of the grouphead under the screen showed almost no coffee residue there and even the inside of the screen itself was very clean.

You're not the first to say something like this Randy. It amazes me to hear it - I always see a noticeable accumulation of black glick inside the screen after a few days of use even though I rinse no less than you as far as I can tell.

I've noticed that the roast and the bean will make a difference. Darker, softer beans leave more residue than lighter harder ones - other than that I just don't know why the variation in oil accumulation inside the screen should be what it seems to be.

Not an e-61 here but I thought I'd add my regimen. I generally brew beans full city and lighter. I pull 2-4 shots a day. After each shot I rinse the portafilter under the group flush. Then wipe out the portafilter and the shower screen. I chemical backflush about once a month or so. I have removed the shower screen after this period before chem backflushing and really didn't notice any unacceptable amount of grime. I don't know, maybe the group really makes a huge difference or I'm just pretty casual about the whole thing. ymmv

There are participants in the forum far more knowledgeable than I, but it could be that a darker roast creates more fines that more easily get past the screen. I roast about 10-15 seconds into second crack. No oil showing save a stray droplet here or there that disappear after the beans cool. I wonder if water content has an effect as well? Dose and head room as well? Just spitballing.

Randy G. wrote:There are participants in the forum far more knowledgeable than I, but it could be that a darker roast creates more fines that more easily get past the screen. I roast about 10-15 seconds into second crack. No oil showing save a stray droplet here or there that disappear after the beans cool. I wonder if water content has an effect as well? Dose and head room as well? Just spitballing.

The darkest roast I run through my machine would be Klatch Belle - darker than many that people brew here but not what I would normally call a "dark roast" by any means. So...I dunno.