Many of you are perhaps familiar with the phenomenon of the first shot of the day on an espresso machine tasting slightly (or perhaps significantly worse) than subsequent shots, even with thorough grinder purging and using identical parameters for shot preparation.

It seems that most of us have come to the conclusion that this is related to residual coffee oils/particulates that coat the brew path between the 3-way valve and the grouphead. As a result, many of us advocate detergent backflushing on a very frequent basis. I personally do this after every session for my equipment. Others recommend the practice of just sinking the first shot to "dissolve" the rancid oils and/or detergent from the group.

I don't have too much to add to that discussion, but I did want to call out, for your consideration, that shower screens may be a significant contributor to this effect.

There's been a bit of buzz on the forums, here and there, around new shower screens that are built a little differently. Whereas normally screens are built by laying a coarse mesh screen over a perforated sheet of metal, these new screens are made from finely perforated/drilled single sheets of metal. For whatever reason, most manufacturers who promote these devices tout their superior infusion or even dispersion, making outlandish claim about improved extractions.

I can't say that I've ever witnessed evidence to give credence to any such claims, but hygiene-well. I recently posted a link from Jason Prefontaine's Instagram showing the exposed "inside" of a shower screen that looked scrubbed clean and pristine before it was cut open:


Source: Instagram

Now, that's pretty over-the-top disgusting. But it's also most likely from a commercial machine that was used very, very heavily, even if it was backflushed multiple times a day. I wondered what a screen from a home espresso machine that is meticulously cleaned might look like.

So I persuaded a very particular fellow home barista to switch out his ~6 month old screen and let me destroy his screen in the name of science. Paul backflushes often, though I don't think he uses detergent every time-still, much more often than the once a week suggested by some on this forum. I detergent backflushed my machine with his screen in my blind basket before shooting these pictures. Here's what I found:


Looks pretty good. Just a couple of stuck particles that can't be scrubbed out.


Totally pristine in the back of the screen.


MUCH cleaner than a commercial machine, as expected-but far from pristine.


The rim of the outer ring in particular traps coffee particles.

I wiped off a little sample of the dirt from the perforated backing sheet and licked it. I found that it tasted a bit like coffee chaff, for the most part. Kinda woody or grassy, and just a little bitter, but mostly just dull.

I thought I would share this with my fellow home baristas, and crowdsource the question-what does your screen look like when you take it apart as above? What's your cleaning routine like?

I do a detergent backflush only weekly, but I don't backflush with the screen in place. I've done it that way since 2009 and I can't remember the source of the advice to do so, but it seemed credible at the time.

However, I always soak the screen, dispersion screw, baskets and PF in hot water with at least a tablespoon of Jo Glo for 30 minutes.

Next time I do it, I'll chop the screen to see if the residue you found on yours is there.

I am still stuck on 'I wiped off some of the dirt and licked it' part. The stuff we do in the name of espresso.

Sorry... another post where I can't remember the reference... but speaking of the first shot being bad... One of the other HBers discovered that if you first put in the backflush disk and bring the machine to full pressure with water, then the first shot with coffee is much better. I have to confirm that I have tried it and it makes a huge difference on the first coffee shot with my machine too. YOu can see the difference on the pressure gauge too. Before the backfluch, the machine sits at almost 0 bar. After, it idles at 3 ish. Give it a try!

Jim

Some type of flushing routine (especially, as you say, a flow-restricted one) can be very helpful in bringing the group to temperature on machines that have groups that idle too cold or too hot, like most E61 machines. For very thermally stable machines with saturated groupheads or highly tuned heat exchangers (like a NS Aurelia), this flushing regimen is not helpful.

There may be any number of reasons that a given machine can taste off on the first shot. Thermal stability is definitely one for some machines. It's important to be familiar with the taste of too-cold/too-hot espresso. Espresso from a dirty group doesn't taste like this. It is usually muddy and has a dull bitterness. It can be very similar to an espresso that's too hot, but it's not the same.

Prefontaine's shower screen insides looks a lot like liquid coffee that has been dried and baked, rather than the tarry insolubles that clog the holes, and that our regular cleaning efforts address. If this is the case; people who simply flush the group after shots should have cleaner screens than ones who do not.

Good point; looking at it, I agree with you that it looks like coffee that dried in layers rather than actual coffee particles (fines, etc) stuck on the group.

The 6-month old sample I pulled out had virtually no residue like that (and I can confirm that it was water flushed after shots shortly after pulling, all the time), instead having a few particles stuck here and there in the space between the screen and the perforated backing plate.

It really makes me wonder if that buildup is due to improper maintenance (like failing to remove the portafilter and flush the group shortly after pulling a shot), or if it's just due to extremely high volume usage. I will try to follow up about that.

Schomer used to recommend knocking out the puck and flushing only immediately prior to making the next shot. This saves a step, so makes good sense for a cafe. But it would lead to liquid coffee drying wherever it might be.

Dried coffee is the same as instant coffee -- so some of it will redissolves and give an excessively bitter taste.

Finally, if dried coffee is on the shower screen, it might also be on the underside of the dispersion block.

Yes, that would work for him, because if I remember right, he also said he takes his brew heads off line for back flushing and cleaning every hour or so. This keeps them from having any stale coffee in them to contaminate the taste. During the day, he's constantly rotating them through a cleaning cycle.

I'm still using the same dispersal screen that came in my machine 14 years ago and it looks just the same now as it did the day I unpacked it. I'm sure mine doesn't get used anywhere near what many of ya'll do but I still knock my puck out and flush my screen as soon as I get through making my extraction. Afterwards, as soon as I get time, I take that little angled brush and run around all over it and around the gasket and flush it one more with the portafilter in. I usually back flush it for several seconds with just hot water before turning it off. I don't leave mine on because I don't use it regularly. About once a week I remove the dispersal screen and diffusion plate and back flush the machine with URNEX. I stick the dispersal screen, diffusion plate and head of the portafilter in an ultrasonic cleaner with a teaspoon of URNEX and hot water, and let it run for about a 1/2 hour, rinse everything off with hot water and put it back together. Everything in the brew head still looks brand new.

Also, if you look at the screen at the right angle and light, you can see the bright metal under it. If you are not seeing bright metal, you probably have a problem. I know sometimes when I've cleaned mine and looked, I could see small dark spots so I would stick in back in the ultrasonic cleaner, a second trip through it, and a good blowjob with 175 PSI of compressed air and it's looking brand new again, no dark spots anywhere.