Please keep us updated on your progress. I'm interested to hear if you ever fully replicate the flavors found at your local shop and what technique did the trick.

So now I tried to reduce the pump pressure from 10 to 7 bar, same temperature (90 oC), hoping to grind the same dose coarser (19 grams) while keeping the same extraction time (around 23 seconds), and increasing the ratio in steps from 1:1.5 to 1:2. The objective is to avoid the bitterness while obtaining a softer body. The results until now have not been promising, but I think I did not let my machine recover enough after changing the pressure (and cycling a lot of water through it in the process).

Maybe my water debit is too high at 110 mL/10 seconds... But I suspect that a lower water debit would only benefit lighter roasts (longer pre-infusions). Well, I will keep you posted.

An easy way to test your water debit theory is with the pre-infusion mode. Set the pre-infusion duration to max (60s?) and then adjust the pressure % down until you reach the desired flow rate. Now pull the full shot during the pre-infusion window.

I have tried everything... Same harsh, unpleasant taste regardless of the recipe. My current beans produce unpalatable espresso (40% washed from Guatemala, 30% natural from Brazil, 30% Robusta from Ecuador, dark roasted, roasted 1 week ago). I tried from dosing low (12g) and grinding finer with a low ratio (1:2), to dosing high (19g) and grinding coarse with a high ratio (1:3), same 30s time, temperatures from 92 to 96°C, and the shots are basically the same - harsh, undrinkable.

That after opening my grinder and cleaning it thoroughly, and backflushing my machine.

There must be something wrong with my equipment... I have had much better shots from similar equipment and much poorer technique (not flushing properly, arbitrary dose, tamping without leveling, no WDT).

What to replace? Grinder or machine?

The robusta might be contributing to the harsh taste unless of course you have in the past got some good shots from it


Randy

I observed the following when visiting a local coffee house that produces amazing espresso with dark-roasted beans:
1. Large baskets and large doses (beyond 18 grams)
2. Shot times on the lower side (23-25 seconds)
3. High flow throughout the shot (large dose, low time => relatively large particle size => high flow)

I have managed to get sweet, heavy-bodied shots this way. Definitely enjoyable, and the best cappuccinos ever according to my wife.
I still can't reach the body and notes that I want for straight shots, though. My ideal shot would have a lighter body and a dried fruits aroma. For more flavor separation and less noise, I'll probably need a better grinder.

Do you know what equipment they are using in the local shop?

drH wrote: Do you know what equipment they are using in the local shop?

Top-notch machine... VA Black Eagle. The grinder is a Eureka Atom.

I was finally able to lower the harshness by doing two things:
(1) decreasing the water debit from 110 mL/10 s to 70 mL/10 s (I actually sold my Rocket Mozzafiato R and got a Lelit Bianca, but this is the only difference in the machine settings).
(2) increasing the dose, therefore increasing particle size.

The shots are still heavy-bodied, but markedly sweeter and fruitier. Enjoyable, but still not what I am looking for - less body, more chocolate and caramel. I am unable to reach that character with my Eureka Specialità, after trying every possibility in the past years. I will try using another grinder with a radically different burr geometry - a Weber HG-1.

Bitterness can be a sign of over-extraction. That you have been able to get better results by both shortening the ratio (less than 1:2, more ristretto) and shortening the time would seem to verify this. If you extract beans too long, you begin to extract the plant fibers, leading to bitterness. Grinding finer, lowering the ratio, and keeping the time between 25-35 seconds are ways to make sure you're not venturing into bitterness. Over time, extraction looks like this: salt/acid----sugars---plant fibers/bitter. So you want to extract long enough to release sugars (not too much acid) but not so long that bitters (some taste this as "cardboard") are released. Lower temperatures can also emphasize more sweetness and less bitter. If your machine is clean and you've tried all of the above, the only other culprit could be the coffee. But it sounds like by your results you're on the right track:).

With most coffees, I find a darker roast tends to benefit from a shorter pull (somewhere between 1:1 and 1:2; shorter results in more body and sweetness. Lighter roasts often need larger ratios (1:2 to 1:3 or more), and often benefit from a hotter brewing temperature, as the lighter roasted beans are less broken down by roasting and are harder to extract.