I'm trying to make comparison between singles pulled with two machines above.
I mean about 8g coffee and single basket.
My Bezzera has OPV set at 12 bar. I did not lower it yet because Elektra has not OPV and in my head I think that only in this way they can compete in a fair way.
Boilers are at 1.1-1.2 bar pressure in both cases, Ulka Pumps were both replaced recently (last week on the Bezzera and a couple of months ago on the Semi) and grinder is the same.

What I find with Bezzera is that it is almost impossible to lower the brewing pressure at 9-10 bar with grinding and tamping. Moreover, after the shot I find my portafilter (under the filter) coated by a very very thin black powder. This mean that grinding is too fine, in my opinion (actually it could also mean that I should definitely upgrade my grinder, but I prefer to ignore this point). Grinding coarser results obtained are not exactly what I want.
Jim in an old post (I still don't get it: Why adjust the OPV?) wrote:

You can adjust your grind and tamp to pull a 9 to 10 bar double; but for singles and ristrettos, you can't. The Italian spec for vibe pumps is to set it to 11 bar on a blind filter. If you can see the pressure during a shot, adjust it while pulling a single or ristretto, so you get 9 to 10 bar.

Well, it make sense and is what I'm finding here.

Looking at SemiAutomatica, I find relatively easier to obtain good singles. I can't say what's the brewing pressure, but I suppose that It should be not so much different from Bezzera.
Again, Jim in its review (/elektra-se ... eview.html) wrote:

The Elektra has no overpressure valve (OPV); so its pressure cannot be adjusted independently of the flow rate, and singles extract at 13 to 14 bar. Quite frankly, a properly adjusted OPV should be on a machine at this price. There is sufficient room in the base and the waste water can be fed directly back into the pump, so a second hose is not required. However, that being said, the missing OPV, quite amazingly, does not affect the quality of the espresso. Machines without OPVs generally make very poor singles, whereas the Elektra's are among the best espresso I've ever tasted.

Again it seems what I'm finding here.

My question is: why this difference?
I admit that Jim's review conclusions "Why is the Elektra Semiautomatica So Good?" doesn't give me the complete answer.
Alberto

That's really odd, since the BZ10's group is very similar to the Elektra's.

My suggestion is to follow another one of my rules: "grind setting, not dose." Use the same grind setting on the BZ10 as on the Elektra and adjust the dose so the flow is correct. That should get you close, or at least closer, to the same taste. I use this trick when comparing different machines or baskets. (When comparing grinders, this doesn't work. To find the equivalent grind setting, adjust the new one to get the same flow at the same dose of the same coffee on the same basket and machine)

I still don't know why the OPV has so little influence on the Semi. I put one in; but setting up an OPV to feed back the water into the pump intake, rather than all the back to the tank, makes the system annoyingly noisy. I was happy I could remove it without ill effect.

What I' m missing on the semiautomatica, mainly in comparison like this, is a brewing pressure manometer.
I'm wondering if some add-on kit could be available to install one on the semi.

For that sot of tech stuff; you may want a different machine. The Semi's style is more seat of the pants.

Finally I lowered the OPV on the bezzera.
I was not able to manage native pressures from the pump at singles flow rate.
Now I'm thinking that perhaps I could have investigated more the effect of brewing temperature.
Pstats were set approx to the same values, but it could be that brewing temperatures were not.
My question is: what should be effects of brewing temperatures little too high or cold? Bezzera singles were all with less body, even if they dropped for 40 seconds from the portafilter. I mean that viscosity of the liquid in the cup was always too low. In italy we think that coffee in the cup have to support sugar for a while. Bezzera's singles never did it. Semi's do.
Alberto

To tell you the truth; the Semi is the only machine on which it was easier to for me, when it was new, to pull good single than doubles. I had to relearn a lot to pull good doubles. But US espresso culture is so overwhelmingly double shot oriented that I put in the time. For some reason, no other machine I've used has been like that. Instead, doubles were always easier than singles. So, in the US, there was no incentive learning thow to make good singles -- nobody was interested.

I'm hoping that as an Italian dude, from the land of singles, you will work harder at them, and then tell us their secrets

Sure I will do.
Actually process optimisation is my work.
But in a real plant I would immediately ask for instrumentations. For example I would like to have data from flowmeter, some temperatures and some pressure gauges.
My feeling ia that I'm really under-instrumented.
Could you tell me something more on the modificationa needed on the semi to get good doubles starting from a good singles procedure?
I could try to learn something in a sort of reverse engineering.
Alberto

algue wrote:Could you tell me something more on the modificationa needed on the semi to get good doubles starting from a good singles procedure?

I had to break my US habits and leave lots of headroom in the double basket. If you see the imprint of the screw that holds in the shower screen, the shot will be bad.

Yesterday I went to one of my favourite bar.
It is a shop owned by a big roasting company.
I bought some grounded coffee. The same grinding they use in their commercial machine at the bar, ground with their commercial grinder.
Now I just tested it on bezzera. Too much flow.
3 bar pressure and 5-6 seconds extraction time.
Machine needs some urgent setting, I would say.
I'm probably going to lower boiler pressure to lower brewing temperature and maybe OPV too.
Alberto

Take a look at the group jet. Is it there? Is it the right size? When I was testing the BZ07, it ran on the same dose and grind as the Semi.