another_jim wrote:I just wait for the coffee to start flowing, than drop the pressure very fast, so the flow stays slow and steady, 3 to 5 bars as far as I can guess. This "profile" is not rocket science; to automate it, all that is required is to detect the start of the flow, and drop the pressure then. The timing of this event is very unstable, so time/pressure profiles, no matter how elaborately done, will not deliver consistent performance.

I see this as the central idea: varying brew pressure to maintain a constant flow rate throughout the extraction. (Most pump machines apply constant brew pressure, resulting in variable flow rates during extraction.)

Presumably this could be automated using a flowmeter (to monitor either the water flowing through the group into the puck) or a scale (weighing the the extracted liquid). That would eliminate the need for any sort of elaborate pressure profiling schemes.

I like the flowmeter idea since I already have one built in!! It should be straightforward to design a system to keep flow steady using a variable pump and a flowmeter!! Call it the WFS, the Weiss Flow System!!

Make sure not to use a constant flow control until you see flow. The early part of the shot, when the puck soaks and fines migrate probably just need fixed pressure or a steady ramp up. If you use a constant flow control at this stage, you'll probably just max out the pump and blow out the gasket.

We are just at the start of all this; and my guess is there will be lots of ways to skin this cat. I got the Strega because the either stupid or inspired combo of 9 bar pump and lever allowed for this sort of experiment.

The odd thing is that I didn't realize until later, as I was pulling 40 and 45 second shots, that having all the water in the 90C group, rather than in a 120C HX, was an absolute requirement for this type of profiling. It requires that the water doesn't overheat, but rather sits at somewhat lower than usual temperatures to compensate for the lengthened brew time. Profiling is a natural addition to dual boilers, but may be problematic with an HX. This is probably why I never got anywhere using a dimmer on the pumps of my HX machines.

I guess there will always need to be manual input to change the profile from say 9 bar during puck saturation to constant flow once the puck is fully saturated. Still, I am intrigued by the flometer idea.

Getting back to pressure profiling, are you suggesting that the reason my earlier attempt at pressure control failed because I should have been reducing the pressure after the shot flowed as opposed to me using lower pressure until the flow started?

Starting slow doesn't do a thing for taste. In low dose shots, the pucks are largely self repairing, and you don't need it either. But when you overload the basket, it's much easier to get a decent flowing shot if it starts soft.

Jim,
Another great post, well thought out, that makes me wish I knew more about coffee..

But speaking for myself and based on my own home experience, with the arrival of the VBM Double here, and paired with the Kony, and applying manual preinfusion to every shot, I have seen dramatic improvement in my espresso, not only in consistency, but also in flavor. Small changes in dose (as little as .2 to .3 grams), and changes in grind setting (like one-half of an increment on the Kony), can be easily tasted in the straight espresso as well as in a cappa. Pressure profiling would be an interesting next step, even if as simple as a timer that drops the pressure after X seconds of the start of the pump, with programmable delay time.

Another solution could be an infrared sensor that would "see" the first drops of coffee from the portafilter and drop the pressure (or adjust the flow rate) accordingly.

We all make excellent espresso (or at least, we've been at it so long that we'd need to check into a loony bin if we weren't); but we are still not at the point were you can pull as good or better tasting shots than brews from every coffee and roast out there. I think these pressure games may be one more step in that direction. Since my personal bugaboo is not being able to make shots from all coffees I like brewed, this interests me a lot.

another_jim wrote: Since my personal bugaboo is not being able to make shots from all coffees I like brewed, this interests me a lot.

Now that would be progress!

another_jim wrote:In the past ten years, it has become clear that when making higher dose shots in the PNW style, the larger planar grinders and conicals do fairly well, while the smaller planar grinders often produce excessively bitter or sour shots.

I don't disagree with this, but my feeling is that it's the lesser problem with smaller grinders. With a few exceptions, like the Baratza Vario (mostly), smaller grinders lack consistency. Even if they were capable working well at coarser grind settings, dialing in with an inconsistent grinder is a painful process, and then producing the same shot every time isn't likely.

If there's any area of espresso technology that needs more attention, it's production of consistent grinders at a lower price point! That may not solve the coarse grind problem, but at least entry-level home baristas will be able to produce good non-PNW shots more reliably.

another_jim wrote:Starting slow doesn't do a thing for taste. In low dose shots, the pucks are largely self repairing, and you don't need it either. But when you overload the basket, it's much easier to get a decent flowing shot if it starts soft.

Maybe my technique is flawed, but sometimes I find that a given coffee will taste better, or worse, if I do line-pressure preinfusion. I've found this to be true of low and high dose shots, varying with the coffee and the flow rate I'm trying to achieve. I haven't been able to determine any pattern on this, just which coffees benefit and which don't.

I've noticed that doses at the very high end (20g-22g, which is rare for me) do tend to flow better with line-pressure pre-infusion, so on that part we agree.

Also, in my very limited production of singles, I find line-pressure preinfusion tends to minimize gushers. That probably has more to do with my bad singles technique and/or basket geometry.

I've experimented with dropping to line-pressure towards the end of the shot, but this has had consistently poor results. Sounds like it's way too late by that time.

I don't think it would work to drop the pressure to 3 BAR after the puck is saturated, but I'll give that a try. It might exceed the 50 second shot limit on the GS/3!