Hi!
I'm a real Italian home-barista living in Turin, Italy. About one year ago I bought myself a Vibiemme Domobar Junior with heat exchanger and a professional coffee grinder hoping to brew the perfect shot. After several trials, my espressos are not as good as I would like them to be. In the family we all drink espresso without sugar and appreciate the "creamy and tasty but mild" espresso shots, but I am unable to achieve this. Although my shots are actually better than most espressos you drink in the average Italian bar, I keep getting some bitterness in the background.

I basically tried everything. I tried thinner and coarser grinding, I tried to increase/decrease the amount of powder, I played with the water temperature in the boiler and the brew pressure, but I cannot seem to get the perfect shot. So far, the best shots have been pulled with powder on the thin side and dose on the low side, but the 25 ml are brewed a lot faster than 25 sec. and coffee is a little watery.

Has anyone suggestions?

Fulvio

Without knowing what sort of beans you are using it will be difficult also...bitter is subjective, coffee always has some bitters in it. Do you have a experience in mind as goal for taste,, or is it that you just want as little bitter as possible?
I'd suggest to find a supplier of fresh roasted beans ( less than a week post roast date) and try some fairly lightly roasted beans, most italian blends contain robusta, and or are very dark roasts and I suspect changing the software may just do the trick for you.
What you describe as flow speed also sounds as beans that are too old for good espresso.

What coffee do you use?

Edit: Looks like Marcel beat me to this while I took a shower, but that is the first thing that comes to mind (not the shower, but the coffee beans). Have you tried fresh beans (about a week from roasting date), or non-Italian roasters?

i heard people like higher brew ratios like 1:3 in italy.
have you tried pulling a shot shorter? with 1:2~2.5 brew ratio maybe?

Marcelnl wrote:Without knowing what sort of beans you are using it will be difficult also...bitter is subjective, coffee always has some bitters in it. Do you have a experience in mind as goal for taste,, or is it that you just want as little bitter as possible?
I'd suggest to find a supplier of fresh roasted beans ( less than a week post roast date) and try some fairly lightly roasted beans, most italian blends contain robusta, and or are very dark roasts and I suspect changing the software may just do the trick for you.
What you describe as flow speed also sounds as beans that are too old for good espresso.

Thanks Marceini and Nick and you all. I'm currently using freshly roasted beans from a nation-wide known roaster (who is also a friend of mine). I buy Harenna Forest from Ethiopia, which is 100% arabic. Experience is, even if I use the same beans as the bar is using, I get more bitterness than I find at the bar. I do have an experience in mind as a goal for taste, which is a bar downtown, in fact that's where I got their beans. Some bars can get creaminess and richness without bitterness while it seems to me that if I get rid of the bitterness the creamy&rich is gone as well. Regarding the brew ratio, I think the extra short ristrettos are probably best for those who add sugar to their coffee, which is not my case. I'll experiment more...

Excessive bitterness is a result of over-extraction. We know that there are three ways to affect your extraction: time, grind and temperature.

I think the suggestion given above to do a shorter shot could be just what you need. Give it a try and let us know if it helped...

Also I wonder what kind of a dose you're using? Are you using a single basket? Usually it is regarded that a double basket will give you better results, or at least it is easier.

And the grinder makes a difference, if you compare your shots to the ones in the cafe...

Agree that the double basket makes a difference but I often need a single espresso (Italians never drink double shots...). I'll come back with the dose I'm using, although i've measured it several times and I'm positive it is in the 7,8-8 g range. Experimenting with shorter pull, getting better

If your machine is a heat exchanger have you tried varying your cooling flush routine? I know you mentioned varying your boiler pressure but didn't see anything about your flush/rebound times.

I'm not familiar with your machine so don't know if it has a reputation for needing much of a cooling flush.

lozava wrote:Agree that the double basket makes a difference but I often need a single espresso (Italians never drink double shots...). I'll come back with the dose I'm using, although i've measured it several times and I'm positive it is in the 7,8-8 g range. Experimenting with shorter pull, getting better

Yes, I know about Italians only drinking single shots. That's why I was asking...

The rest of the World (ok, that is exaggerating, but maybe the speciality coffee people) use mostly double baskets (at least the way I see it, don't shoot me if someone disagrees).
What you could try, is to dose into a double basket (something between 14-18g) and pulling only the size of a single shot. Keeping the ratio no more than 1:2.
I obviously don't know much about the roast level your beans, but since you are using Ethiopian (which often is not at it's best when roasted dark) this might work.
Have you asked from the cafe what kind of a dose they use?

What kind of cooling flush routine do you use?

What kind of water quality do you have?

Have you cleaned your grinder recently? A dirty grinder can contribute to off tastes.

Do you regularly clean and back flush your espresso machine? You should do plain water backflushing every day. And detergent backflushing every few weeks depending on your use. Lots of bad tasting gunk and oils can buildup in your machine leading to bad tastes.

As mentioned, use a double basket. They're much, much easier to work with.