endlesscycles wrote:Solubility of solids is unrelated to pressure.
Pressure has no impact on the solubility of solids.
Got it?

Pressure is one way to control flow rate which is what ultimately has an impact on extraction.

Flow rate through the puck, after preinfusion, didn't have a noticeable relationship to extraction in the shots we logged, however there did seem to be a more tangible relationship between overall shot time & brew ratio.

Look at the two shots at 2.44:1 ("24.4" on chart), one took 31sec total with 10sec pre-infusion & slow ramp to 9BAR, the other 30sec total 15sec pre-infusion then flat 9BAR.
One had an average rate of flow through the puck of 3g/sec, the other 2g/sec, but very similar overall shot time and yield. Similarly, the 2 shots at 2.3:1 ("23.1" on chart) had average flow rates of 1.86g/sec & 2.42g/sec but, again, very similar in the other respects.

A factor that did seem to have some relationship to target shots was total shot time vs brew ratio. In a time vs mass context, this could be expressed as: Total shot time/brew ratio, e.g. 34sec/2.48:1 = 13.7sec.

All MrBoots' shots that fell in the target zone (21%EY+) were between 9.6sec & 14.6sec. (Caveat: for brew ratios between 2.24:1 & 2.62:1.)
The two 2.44:1 shots were 12.3 & 12.7sec in this respect.
The two 2.3:1 shots were 12.6 & 13.9sec in this respect.

endlesscycles wrote:Solubility of solids is unrelated to pressure. Pressure has no impact on the solubility of solids.

True pretty much. However, pressure does make quite a difference for the solubility of gasses, and gasses are an important part of espresso, e.g., crema.

And while we're talking about flow rate, we have to bear in mind that "solubility" and "rate of dissolution" which is also at issue in a timed shot (rate = volume/time) are related but different things.

Pressure is one way to control flow rate which is what ultimately has an impact on extraction.

You're carrying the limitations on pressure too far. For instance, we're all familiar with the paradigm of a machine running over pressure which requires an OPV adjustment in the case of a vibe pump or a pump adjustment for a rotary. That is, a shot extracted at a pressure greater than 10 bar tastes differently from a shot extracted at 9 bar at the same flow rate, tending to bear aromatic and flavor hallmarks of over extraction.

Since the 10+ bar shot at a given flow rate represents a greater load on the pump circuit, we can speculate that a difference in grind (finer grind = greater surface area = faster rate of dissolution; finer grind + given dose = greater load) makes the difference in taste and pressure per se; but in any case, this widely experienced phenomenon runs counter to your argument that flow rate alone is responsible for the differences in taste.

Rich

I think spring levers have it right. Low pressure preinfusion to wet and degass the coffee, followed by high flow rate of fresh solvent, smoothly decreasing to lower flow of fresh solvent. Assuming the goal is the strongest coffee of the desired extraction... and if it isn't, then I don't know what espresso is supposed to be at all.

Having tried coffee from a range of different roasters and regions, I find that sometimes the spring level profile works well, sometimes it doesn't.

endlesscycles wrote:I think spring levers have it right. Low pressure preinfusion to wet and degass the coffee, followed by high flow rate of fresh solvent, smoothly decreasing to lower flow of fresh solvent. Assuming the goal is the strongest coffee of the desired extraction... and if it isn't, then I don't know what espresso is supposed to be at all.

I like the theory of this... however I like the ability of a pump to emulsify coffee bean oils and produce that extra something in terms of mouthfeel.

I did make a post last night to this thread, but it appears to have disappeared....was it moderated out, I can't think why it would have been? Luckily Lazarus is my friend in these situations, so the text recovery is below....addition. Looks like I might have pressed preview instead of submit, have been informed nothing was moderated...<i must be getting old>
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I think the difficulty here is the possible confusion between the pressure/flow relationship.

1. Flow profiling is not pressure profiling and vice versa....they have an impact on each other, but are not 2 different ways to skin the same cat!
2. How the pressure is applied, rate of increase makes a big difference...
3. The length of preinfusion makes a big difference...

For the next machine I am helping design, I have made some specific specifications that does go some way to address the issues of pressure vs flow, but don't feel I can say any more at this time.

Ultimately the arbiter is taste, I know people love the machines and the science, but I know what looks good and tastes good and at the end of the day, that's all that matters. on a Vesuvius, with the same coffee, some profiles taste bad, some taste good...and these can be very similar profiles, not necessarily massive differences. The ability to control pressure also seems to increase the number of successful shots (by this I mean the very good ones), but it does need a really good grinder. Without a really good grinder, you run into problems when grinding really fine. It also makes comparisons between standard machines very difficult, because you can't use the same grind in both....if you are able to, then perhaps you need to look at the Vesuvius profile.

For me it was all about being able to grind as fine as possible, but not over extract the final product...to get the good flavour and as much of it as I could, whilst leaving the undesirables behind....certainly reducing pressure towards the back end of the shot has always seemed to help with this....as does the very gentle application of full pressure at the front end of the shot.

pizzaman383 wrote:Flow rate and preinfusion time also have an impact on temperature at least on some espresso machines. That may be the source of some of the flavor differences because we know that solubility of the taste compounds changes with temperature.

Maybe we need to measure and graph the actual puck temperature and the weight (as a proxy for flow rate) during the different profile shots.

I'm with you. To me it seems like any discussion of pressure profiling on taste can only be complete with thermometric data, especially because it appears from the data and anecdotes presented here that the effects of pressure on taste are not nearly as sensitive as the effects of temperature on taste. Regardless of machine design, the actual puck temperature will be changing, from room temp to the brewing temperatures.

It seems like pressure profile could have two influences on the flavor extraction as a related to puck temperature. The pressure at a given time will govern the flow rate at a given time and the flow rate will govern both the temperature of the puck at that time and the amount of beverage through the puck at the temperature and time. You could imagine a simple concept that there would be a pressure profile that would lead to the greatest amount of beverage produced at the optimal temperature for that coffee.

sarpar wrote:How does Bar pressure affect taste in the espresso shot?

I"m not only thinking of pressure profiling ala Vesuvius, but how might 8 Bar taste (all other parameters the same) vs 10 bar?

I"m assuming you can get a higher extraction percentage with higher pressure but will that make for a more bitter shot, or a sweeter shot, or just more intense?

I guess I'll go try it out on my machine, but I figured you all out there could help me understand why.

Sarah

In my opinion, required reading if you haven't seen it already, which should explain the why (I hadn't seen it linked in the thread yet, but apologies if redundant):
Pressure profiling, flow profiling, and a new rule of thirds

After getting more experience with various profiles, I can give my impression. To me, more or less, exact pressures don't make a huge difference in shot taste. What profiling really opens up to you is the ability to grind much finer on lighter roasts, but still get a normal flow rate by using a very low pressure (1-2 bar) ~20-40s pre-infusion. Still a too quick ramp to full pressure after that pre-infusion will end up compressing the puck too much, I like to go up to full pressure over 5 seconds or so, rather than instantly.

Other factors certainly affect a shot, it's not all about pressure. Temp still matters, grind still matters. But being able to vary the pressure over the course of a shot certainly has it's benefits, especially with lighter roasts. FWIW, I usually don't use the long pre-infusion profile when pulling darker roasts, in that case a relatively fast ramp to a moderate full pressure ends up accentuating what little fruit flavors are left in dark roasts for me.

Also it's worth noting, all my testing has been with conicals, maybe an EK43 or so would be a lot different, I'm not too certain there.