I am a german user having the problem, that the taste and consistency of espresso in both cups are quite different. The machine is leveled, brewing ratio 2:1, the result tasty but clearly different left and right.

It appears as if due to (eventual) channeling an uneven flow containing two streams enters the common central hole and these "streams" do not get mixed on the way to the two outlets. Very strange from the technical point of view, or has anybody experienced something like this?

Thanks!

There should be no difference. Does equal amount of espresso flow to each side (based on weight, not visually)? If no, that's an issue, indicating channeling. You need to figure out why this is happening.

If you have a bottomless portafilter, that helps diagnose. You have to improve puck prep. Let us know how you prepare a shot.

Yes, logically there should be no difference.
There is indeed some height difference of the machine but really minimal. And a little diff. In the height in the cups. As there is just ONE hole for total flow, at latest after these 4-5 milimeters of the way through it any fluid should be homogen - I think independent of the machine position.

I have to supply a bottomless portafilter and see if I will be able to explain the phenomenon. I will keep you informed, as it will take some time to buy the PF.

Preparation: the powder directly in the portafilter of the integrated mill (lelit PL042TEMD) and measuring the weight, then WDT and tamper. Here I still have difficulty to hold straight. Cups on the scale and measure time/output.

Edit: the portafilter cannot be fully inserted, just about 45 degrees. Everythig perfectly tight.

I have sometimes noted that the flow into the two spouts differ over time. So that in the beginning of the shot one of them gets more coffee and in the end the other one gets most of it. I guess that would also have an impact on the taste, although I have never tried it.
Nowadays I always use my naked portafilter and if I want two singles I will just do two shots after each other using my vst 7g basket instead splitting a double.

Hi Johan, what you describe may really be the explanation! Instead of "two streams simultaneously through one hole" we have different streams at different times of extraction which makes sense with strong channeling. This should be clearly visible wih a bottomless PF. So now I have another base for finding out what really hapens. Thank you so much, I already begun to think that I was talking of ghosts!

When I had just started my own home espresso journey, I got this problem all the time. I don't pull many shots this way anymore (just using a single basket in a bottomless portafilter now), so I'm not sure if things would be different now. But I agree with what's been said so far: it's most likely due to bad puck prep and what Johan said: the different cups get different parts of the extraction (most likely one will taste sourer than it should and the other one bitterer than it should).

Another thing to bear in mind is that the sweet spot in terms of grind size for many coffees can be really, really small. If the grind is too tight, the coffee may exit the basket in a really thin mousetail and, depending on how the portafilter spouts have been designed, there may just not be enough volume for the liquid to go through both of them. (I experience this with my ECM double portafilter which clearly is "internally" out of level, i.e. even if I level my machine and grouphead perfectly, the portafilter is still wonky.)

Henri, I could perfectly follow your experience. Back to my case:
Yes, if grind is too fine, first there will be some oily drops on one side. This is not the case, as I found out approx. the "right" grade. As to the visual observation, both spouts start at the same time and have apparently same appearance. But measuring the liquid in both cups indeed shows in average +/- 3 gramm difference (based of 35 gramm = 17.5 x 2 total.) Mostly the coffee taste in the more full cup is better, yet not always. Makes crazy...

I hope that the not straight (30 degrees) position of the portafilter has no influence. It remains the preparation. Tampering really seems to be the issue. If there is portafilter "internal" problem, what can do, it is original Lelit one. It is not nice, when my wife and me instead of sitting and enjoying the espresso first must ask each other "how is your one" and eventually change the cups.

From many reports I know that single basket is difficult to handle and I am not ready to start experimenting from the very beginning. It really seems that the bottomless porta will give better indication.

I find this to be an intriguing question, and one for which not much data is necessarily available, since most home users drink doubles anyway and cafés that serve singles don't necessarily aim for the kind of perfection that you are after. +/-3 grams, is that much? Quantity-wise, it seems little, but as we know, in the world of espresso, even a single gram can make a difference in taste! Sometimes it can be maddening indeed.

Standard single baskets are indeed frustrating to use - there's a reason why many people immediately throw them in the bin. If you're serious about giving single shots a try, however, I can warmly recommend the straight-walled La Marzocco 7g basket or one of its derivatives, together with a dosing funnel and a matching tamper. See this long thread for more. Having used one for about a year, I now find it easier to pull singles than doubles.

3 grams, maybe 4, are 10 % of a total of 35 grams which are the target to obtain from 17-17.5 grams. I think it is not a difference to be ignored. It seems to be the evidence for a wonky component in my system possibly having been localized in your setup as a "poor" portafilter.

On another hand I can not imagine that an ECM portafilter as in your case features poor quality! Have you ever tried another PF ?