AndyS wrote:If one considers a gentle preinfusion to be "pressure profiling," it is not hard to prove an effect on the extraction.

With a gentle preinfusion (say, 15 sec before 1st drop appears) as opposed to a minimal preinfusion (say, 5 sec before 1st drop appears), one can grind slightly finer and still achieve a comparable flow rate. The finer grind/preinfusion technique results in a slightly higher extraction yield (by maybe 0.5%) which is measurable via refractometer. I'm not sure if a 0.5% difference can be reliably tasted, but given the right coffee and the right tasters, it may be possible.

That's an interesting idea, and something I could easily do manually with my paddle machine. It's sufficiently interesting that when I have some more time I think I'll play around with it. I do (occasionally) go back to line pressure at the end of the shot, some of the time to "salvage" a briskly flowing shot, and sometimes because it looks cool. I have no evidence that this makes any difference whatsoever in shot quality.

ken

erics wrote:A lower flowrate increased dwell time a relatively higher extraction during the last stage.

That's the theory of the "thought experiment." But if one does the actual experiment, one finds it is very hard to get a significant and replicable change in extraction this way (leaving aside the matter of whether the change is desirable).

It also begs the question of whether a similar (or better) result could be achieved by say, raising the brew temperature a couple degrees F (higher temps dissolving more solids).

erics wrote:In the last stage of brewing, there is a noticeable decrease in the surface tension of the flow indicating (to me) that extraction has run its useful course. At this point, I stop the shot and the result has, for the most part, always produced a yummy beverage. A couple of years ago, there was a post on CoffeeGeek describing this surface tension reduction with a most appropriate term - only wish I could remember the word used now.

Reduction in viscosity?

Hoffman just did a post bout pressure profiling, here's the link:

http://www.jimseven.com/2010/11/14/wher...profiling/

WOW! This has been a long time coming. It's cool to see the debate going on here since there has been a whole bunch of talk throughout the years about profiling (pressure and temperature). Talk about passion for espresso!!!!!
The biggest thing I learned in this business is that everyone has an opinion. Since this is a sensory based experience each opinion must be taken seriously. And because we are talking about coffee most everyone has a different experience drinking the same coffee. Most however can agree on what tastes bad.
Here is my take on pressure profiling. Since early 2003 I have been involved with some sort of pressure profiling. In the beginning it was with a small gear pump made by fluid-o-tech and several things after. We actually brought an individual boiler machine with pressure profiling to the SCAA show in 03. It was to demonstrate the serviceability of a removable boiler a few saw the pressure profiling but I can't remember anyone who was really interested (most were looking a the new Hybrid-FB70 machine that we produced for Intelligentsia. I cannot remember that the increase in quality or taste was ever as huge as we saw with "temperature Stability" in the late 90's. However, there were a couple of roasters that ran with the technology and actually came up with a couple of profiles that worked with their coffee (after much experimentation). The thing about pressure profiling was its inability to be transferred across the board like temperature was. Each coffee worked better on a different profile, and you had to find that profile somehow. Not an easy, or inexpensive, task for a home-barista.
What I did find to my surprise what a few profiles that actually opened the "forgiveness band". Meaning that while using a given profile you could produce more consistent shots when other variables (namely tamp and grind) varied slightly. This is the topic that intrigued me the most especially as a home enthusiast.
I believe that any improvement is a good improvement. Some may be satisfied with what they have and not want anymore. Others will continue on their quest to find their best. Can't wait to see what 2011 holds.

One think I forgot to mention. What I have learned over the years is that the term "Stability" has been used very loosely. The most important task of an espresso machine (IMHO) is that it removes the variable of pressure and temperature from the process. In other words it is repeatable and consistent. On thing I have noticed with pressure profiled machines with electronic feedback (i.e. pressure sensor) is that they compensate (weather good or bad) for tamp and grind. Meaning that if you tamp loosely you will have the same pressure readings on the gauge as when you tamp really tight. Essentially the machine is performing differently for each shot you make (please remember I am only the messenger). This all has to do with the physical properties surrounding pressure and flow rate of water. They are both dependent upon each other so if you change one the other is affected.

Billc wrote:WOW! This has been a long time coming. It's cool to see the debate going on here since there has been a whole bunch of talk throughout the years about profiling (pressure and temperature). Talk about passion for espresso!!!!!
The biggest thing I learned in this business is that everyone has an opinion. Since this is a sensory based experience each opinion must be taken seriously. And because we are talking about coffee most everyone has a different experience drinking the same coffee. Most however can agree on what tastes bad.
Here is my take on pressure profiling.

(Snippage)

The thing about pressure profiling was its inability to be transferred across the board like temperature was. Each coffee worked better on a different profile, and you had to find that profile somehow. Not an easy, or inexpensive, task for a home-barista.

What I did find to my surprise what a few profiles that actually opened the "forgiveness band". Meaning that while using a given profile you could produce more consistent shots when other variables (namely tamp and grind) varied slightly. This is the topic that intrigued me the most especially as a home enthusiast.

Hi Bill,

Your post is just about the best summary I have read, of where we are with pressure profiling in late 2010. Thank you.

When you speak about "forgiveness band," (which I think that Dan K. here often calls "Forgiveness Factor" in machine reviews), and how pressure profiling effects it, would you agree that a big element, maybe the biggest part of such a profile, is the presence of a slow pressure ramp up, e.g. "pre-infusion," before the coffee puck is hit with the full-on pump pressure during the "main" part of the extraction?

This is the only aspect of "pressure profiling" that I have found personally to have consistently positive effects (regarding "forgiveness").

ken

AndyS wrote:Reduction in viscosity?

I'll guess that this all happens when you reach the "Yummy Point" (technically speaking - the exact point in time at which maximum yumminess has been achieved.)