(mod's note: Moved from Bricoletta's Bench thread)

malachi wrote: I checked brew pressure on the machine and it was higher than I like (10.25BAR). But I didn't really want to bother with it. Today I decided to suck it up and dial the brew pressure in to where I like it (right between 9BAR and 9.25BAR).

So even with the Flojet pressure variations (described in the "Flojet and rotary pump questions" thread), with this setup you are able to dial in the brew pressure and maintain it within 0.25 bar?

malachi wrote:I got it dialed in and pulled a shot of the Hairbender that was all I wanted it to be. Dense, rich, heavy in chocolate but with all the fruit and acidity desirable. Layered and complex but with great definition of flavour.
Wow!!
And Hmmm...

After some more work I had an idea. I did a quick re-plumb to get rid of the FloJet and the water filtration unit. Clarity gone. I then hooked up the FloJet without the water filtration unity. Ah Hah!!! Clarity still gone!! Excited now, I replumbed with no FloJet and no filtration and logged brew pressure. Flutter!! Same with the FloJet and no filtration!! And then with the FloJet and the filtration unit... No Flutter!!!! And clarity!!!

So... new theory (just waiting for Jim or Barry or someone to disprove it) is that it's the combination of brew temp profile and consistent brew pressure profile that creates this clarity.

In trying to understand your theory...do I understand you correctly that you are talking about two distinct pressure parameters:
1. brew pressure profile, a curve that defines the nominal brew pressure value through the course of a shot
2. brew pressure flutter, a description of the fraction-of-a-second water pressure vibrations produced by the pump?

Concerning flutter, vibe pumps produce their eponymous pressure waves at 60 hz. Rotary pumps produce pressure pulses each time a vane passes by the outlet pipe. This works out (in N America) to be about 115 times a second (115 hz).

It's possible to greatly reduce flutter using a "water hammer arrestor" (part number 2522K14 at Mcmaster.com). Also, running the brew water through a gicleur reduces flutter.

With this setup, I was able to maintain pressure to a tolerance of more like 0.10 BAR. Keep in mind that I'm isolated from the water lines so no changes due to flushing toilets or the like and that I have a rather large water filtration canister inline.

Actually, I'd say there are two parameters and one "condition".

1) starting brew pressure (how consistent and accurate is the brew pressure at the time a shot starts - also could be called inter-shot brew pressure consistency).
2) brew pressure profile (what is the brew pressure over time during the extraction of the shot - also could be called intra-shot brew pressure profile or the like)

Condition - rapid oscilation in the pressure during a shot. In other words, is there "flutter" in the brew pressure profile or is it stable through the profile (or along the profile).

I think that there are probably going to be a number of effective strategies for managing brew pressure and the pressure profile over the course of a shot on various kinds of machines and on various pumps. And I think they're going to be very important.

malachi wrote:I think that there are probably going to be a number of effective strategies for managing brew pressure and the pressure profile over the course of a shot on various kinds of machines and on various pumps. And I think they're going to be very important.

The Versalab machine addresses the problem of managing brew pressure with an active control system. John Bicht told me that he was shocked to find that changes of 0.1 bar made a difference in flavor.

It really isn't that difficult to PID the pressure loop on your espresso machine using existing technology. This would give you the ability to accurately "sculpt" the profile if you wanted the pressure to rise or decline during a shot. Currently the implementation is relatively expensive, but if everyone insisted upon having this, the price would go down considerably.

Meanwhile, installing a water hammer arrestor to reduce "flutter" is dirt cheap. I've got one on my machine, but I haven't played with it in a while. Your comments have made me itching to compare results with and without it. I'm just not sure that the difference will be discernible amid the "noise" of my amateur dose/distribution techniques.

That's an interesting point.
I wonder where the threshold is. Honestly, I expect that trying to manage (in some way) your brew temp profile and brew pressure profile is going to result in some amazing results for a lot of people.

I had three shots this morning... clarity. In all three.

It feels so good.

What is interesting is that either, alone, seems to have minimal results when it comes to this ellusive and desired attribute. Temp stability without pressure control doesn't result in it and pressure control without temp stability doesn't either.

In addition, I've noticed that the so called "flutter" is greater with the FloJet and no filtration than without the Flojet or filtration. But even with the latter there is no clarity.

Today I'm going to go and check out espresso from three different Mistrals. One isn't temp modified and doesn't have any sort of pressure "isolation", one is temp modified by doesn't have isolation and the third has both.

A definition of "clarity"...

The experience of tasting an espresso blend and being able to taste not only each bean in the blend, but all of the component flavours of each bean - and having each flavour be clearly defined on the palate.

Imagine a range of colours all together and seeing each colour distinctly rather than having the colours blended together into a flowing gradient of browns to greys.

This is not to say that "clarity" is a required attribute for good tasting espresso. It's an abstract concept and one that I honestly don't know matters to a lot of people.

I'm working on tweaks to brew pressure to see what the results are. One thing I'm beginning to note is that it is possible (perhaps even likely) that there is going to be an optimal pressure profile for each coffee just as there is an optimal temp profile for each one. Now that I've said it it seems downright obvious and I'm sure millions of people have thought of it before.

But it's new to me in the sense that not only is the stability and accuracy of the profile required, the degree of accuracy required is quite fine indeed.

Given the inherent lack of control in the (very manual, very mechanical) adjustment of brew pressure, experimentation is proving to be time consuming.

malachi wrote:A definition of "clarity"...

The experience of tasting an espresso blend and being able to taste not only each bean in the blend, but all of the component flavours of each bean - and having each flavour be clearly defined on the palate.

I think I know what you mean. At the 2004 SCAA show I tried coffee from the Versalab machine. Afterwards, I wrote this comment on alt.coffee:

As far as the flavor goes, the word that came to mind was "transparency." It
seemed like you could look into the blend clearly and taste whatever was there
to be tasted.

Sadly, they screwed things up at the Seattle SCAA, and the coffee was nothing special.

malachi wrote:I'm working on tweaks to brew pressure to see what the results are. One thing I'm beginning to note is that it is possible (perhaps even likely) that there is going to be an optimal pressure profile for each coffee just as there is an optimal temp profile for each one.

Just a related point to throw into the discussion: in my experience, the speed with which the pressure ramps up at the beginning of the shot is a significant part of the pressure profile. This isn't regulated by the Procon pump itself, it's regulated by using a gicleur or a needle valve downstream of the pump. On my machine, a near-instantaneous pressure rampup (as on many gicleur-less Linea AV machines) required a coarser grind adjustment (to maintain shot timing) as compared to the grind needed with a more gradual (~4 sec) pressure rampup.

Excellent point.
I think all the machines I've experienced this "clarity" on either have a slow ramp up through some pre-infusion methodolgy or have downsized to the .8 or even .6 jet.

I'm sure this has been asked before, but why do you guys use a tank and flojet before the pump to keep it stable rather than a simple pressure regulator?

thanks

Keith