I've had a Barista Pro for quite a while now and for all this time I was trying different coffees every week to see what I like more. Never really had problems with dialing-in, I follow some specific guidelines and try to adjust to taste, I get a very decent result but still I've gotten used to the fact that I'll never be able to match the flavor of the same bean from a coffee shop.

Lately, I've decided that I really love Ethiopian beans. So I got me a bag of some freshly-roasted Ethiopia Gigesa. Tried with 17.5g in, aiming at 40-50g out (for iced espresso) at around 28s (including 8s pre-infusion). After dialing-in, I finally found the settings for a very acceptable coffee, that still was kind of bitter (muddy?) that still had many differences compared to the same coffee I drank at a shop.

One day, after talking with a barista, I tried with 18g in, 40g out at around 23s (Temperature at one click lower than the default). The result was the best coffee I've ever tasted, rivaling even the one from the shop. It was sweet, tea-like, fruity, even some florals came through. From that day, I cannot for the life of me repeat this extraction. Tamping-distribution are out of the equation here since I've taken steps to try and keep them as constant as possible between shots, so it has to be some other factor. Right now, with the same settings (18g->40g, 23s) I'm getting a coffee that's bitter, not-at-all bright, kind of muddy, while acidity is replaced by saltiness (Savory?), no fruit and definitely no florals. The body also tastes fuller than the tea-like quality of my best result.

This inconsistency is driving me nuts. If I lower the dose, it flows very fast and is very acidic, not in a good way. If I lower the grind or increase the dose, it starts getting muddy and bitter, like it's over-extracted. If I let it flow for less time, it gets acidic and under developed. If I let it flow for more time, it gets bitter and burnt. If I raise the temperature, it gets bitter and tastes burnt. If I lower it more, it's way under-developed. It feels like there's no sweet spot, but I know there is since I hit it the other day (best coffee ever).

Could someone provide any insight as to why this may be happening or what I should do to combat it?

More information: I'm using a bottomless portafilter that shows no channeling (apart from the first couple of seconds after pre-infusion), the flow rate looks satisfactory, there are no jets spewing coffee all over my kitchen, I use WDT to distribute the coffee + a couple of taps, tamp weight is always the same (palm tamper with depth configuration), I take 2 empty shots with the portafilter on to get everything up-to-temperature, my puck is kinda watery/muddy on top but very firm and ejects in its entirety with one small tap on the trash can. Also, I use tap water and I should have replaced my water filter 2 months ago.

Thanks for the long read!

Rookie home barista