Having reduced the brew pressure by adjusting my OPV to just under 7 Bar, I'm now experimenting with grind and dose, getting some much improved and very nice naked portafilter extractions (35s - 45s range). While I can't do real time pressure profiling on my expobar, I am noticing more flavor notes in my home roasted SO coffee. Thank you for all the helpful tips and suggestions - I'm now at a new level in the coffee universe.

I've been using the Rossa PG Air Espresso for several weeks and I enjoy experimenting with pressure profiling. I've managed some very tasty shots at 5 bar. This device allows real time adjustments and very precise control.

I can make a distinct pre-infusion pause at .5 bar and then quickly ramp the pressure up to 5 bar. I can do a slow and steady ramp up to 6 bar with no pre-infusion pause. I may decide I want to try a certain profile but alter the pressure real time based on the flow rate I see and hear. Another bonus is precise control over temperature without doing the water dance.

I like the fact that I am working in a largely unknown world of variable pressure control. My Rocket Giotto Evoluzione now serves as a very expensive milk frother.

another_jim wrote:I've been using the Bezzera Strega, a pump/lever hyprid for about two years now; and have become convinced that declining pressure throughout the shot, after the flow starts, improves shot quality. If one uses a pump, the flow accelerates and gushes by the end of the shot. If you can lower the pressure smoothly, the flow remains even. Doing this manually rather than using a preset program allows for perfectly even flow; but even a preprogrammed declining profile will get close to maintaining even flow.

Some of the participants in this thread have said they got good results by lowering the pump pressure on their non-profiling machines. But I remember reading threads several years ago about attempts to do that, with inconclusive or unsatisfactory results. It would seem that it's not just a matter of using a lower constant extraction pressure, but of steadily lowering the pressure through the course of the shot. After all, if it was that easy we wouldn't need fancy machines to do pressure profiling!

From your description, it sounds like flow rate is the key. Variable flow rate (or really an accelerating flow rate), which you'll get with constant pressure, doesn't work as well for some coffees as varying the pressure to keep the flow rate constant. It sure would be nice to know what's going on in the coffee to make this true.

One question: Is it really that a constant flow rate works better for SOs, or is it because the SOs we tend to drink are typically roasted lighter than blends, and it's the roast level that makes the difference?

I have adjusted the pressure on my Vetrano pump down to 7.8 - 8 bar and I've found I like the flavors there, better than at 9 bar. I can tell a difference, even though I'm not lowering pressure towards the end of the shot. FWIW, I get more chocolate flavors from the lower pressures. The mouthfeel is more "airy" for me at the lower pressure too. My flow rate at the end of the shot is slower, too, compared to 9 bar.

The one caveat, and it's been mentioned before is that lowering the pressure slows the flow rate and on some machines that can lead to increased brew temps as the shot runs since it will run longer and slower. I've had some shots run almost a minute!

It's always interesting to read Jim's insights on these questions. The only evidence I have to backup Jim's hypothesis is six years of great tasting espresso from a spring home lever machine (probably peaks below 9 bar before declining). I've long noticed that these shots take longer, and that overheating is not an issue during this extended time.

An interesting variation with the home lever is that one typically uses two or more pressure cycles to extract a 15g:30g shot. Not sure if many other people experiment with two or more pressure peaks.

PC

another_jim wrote:I've been using the Bezzera Strega, a pump/lever hyprid for about two years now; and have become convinced that declining pressure throughout the shot, after the flow starts, improves shot quality. If one uses a pump, the flow accelerates and gushes by the end of the shot. If you can lower the pressure smoothly, the flow remains even. Doing this manually rather than using a preset program allows for perfectly even flow; but even a preprogrammed declining profile will get close to maintaining even flow.

I agree with this from experience. Once you raise the pressure to a desired level on the Rossa PG and do nothing, the pressure will reduce automatically during the shot. I have also experimented with maintaining a constant pressure by slowly opening the valve. I've also closed the valve slowly and quickly to accelerate the pressure ramp down. I've also experimented with two pressure peaks.

another_jim wrote:The effect on taste is simple. Espresso blend traditionally have muted acidity and roast flavors, so the coffees taste somewhat dull when brewed normally. This is because in espresso these high and ow flavors are amplified and distorted. This effect disapears when you drop the brew pressure and maintain even flow. The upshot is that you can use a much wider range of coffees and roasts for making shots. If SO espresso becomes more common, you will see most high end cafes that use them going to profiling machines.

+1 Same SO beans, same roast, same dose, same grind -reducing pressure to maintain even flow tastes better than maintaing a constant pressure IMO.

another_jim wrote:There is a caveat here. Profiling to keep the flow steady extends the length of the shot from about 25 seconds to about 35 to 40 seconds. In most HX machines, the water would be overheated by the end of so long a shot; so this requires either a double boiler or classic lever machine (or a specialized group that holds the two ounces of water used for the shot).

I would add a third device to that list. You can do very precise pressure profiling with the Rossa PG Air. I'll never go back to using my E61 machine. I can preheat the device to maintain a constant temp or allow a gradual decrease in temperature but overheating is never an issue. After using this completely manual system and experimenting with variable pressure I sort of understand the "lever guy" thing however I may have more precise control over the entire process. I used this information to get started and the pressure variations I make now are based on personal taste.

Having learned about the Rossa HC from coffeedom on this thread, I took the plunge and now am enjoying pressure profiled shots from this amazing machine - this is really a great option for the home brewer. I'm in the early stages of exploration but thought I'd provide a few insights and results to date. I've found that the unit requires three pre-heat cycles in order to get the brew temperature up above 190 F. Each one of these cycles involves filling the unit with boiling water and waiting for 40sec. With a starting temperature of 64F for the Rossa and using a low mass type K thermocouple to measure the water temperature inside the plunger, I got the following results for the temperature of the water in the Rossa at the end of each 40sec hot water fill cycle....

Cycle 1 - 151F
Cycle 2 - 176F
Cycle 3 - 186F


Below is an image of a naked portafilter shot extracted from 18gm of Highwire's Papua New Guinea Sigri SO coffee. This was done with a grind of 5 on the Rosco handgrinder (pretty fine), with a 15 sec preinfusion at 3bar, followed by a short ramp up to 8bar and then back down to 5-6bar keeping the flow as constant as possible (thin ristretto-like stream). The extraction time after getting up to 8bar was about 50 sec. The shot flavor was complex, smooth and syrupy.





mitch236 wrote:The one caveat, and it's been mentioned before is that lowering the pressure slows the flow rate and on some machines that can lead to increased brew temps as the shot runs since it will run longer and slower. I've had some shots run almost a minute!

This makes good sense and I'm sure there are a lot of variables involved. My experience has been, on my machine with no change in grind, an increase in my 2 oz. shot time from 25 to 30 seconds - but never a minute. I'm willing to live with that difference for the better flavor. I'm using Kenya Nyeri AB Gatomboya SO.