Do ultra precise brew temperatures really matter? - Page 2

[RapidCoffee]

Much more interesting (at least to me) is the related question: is a flat temperature profile more desirable than the humped temperature profile produced by many HX machines? I'm sure that brew temperature differences can be tasted in the cup. But do you get a better extraction when the temperature is varied slightly during the shot?

Unfortunately a much more complicated hypothesis to test...

[Ken Fox]

Short answer.

Yes.

Having used a LM Linea for 15 months and then using a Synesso for 2+ years now, I can say not only does the stability matter, but the control over it matters as well. That's not to say that a specific declining temp profile may not do wonders as well, but for targeting select sweet spots in various espresso it makes a remarkable difference.

This statement by Malachi during his GS3 testing days has always stuck out to me.

You are right, it is a remarkable statement. And I doubt the ability of the equipment to actually deliver shots with that degree of brew temperature accuracy, and as well the capacity of the human tasting/smelling apparatus to detect it.

And I'm not talking about casual tasting when looking at some sort of temperature readout, I am talking about real and verifiable shot temperature measurements with that sort of accuracy, which I think the current crop of probes and digital thermometers cannot reliably deliver on a repeatable basis.

As to the human sensory capability of detecting that, I would personally require blind tasting studies before I would believe it, as I personally believe that this is beyond the capability of just about any human being I know of.

ken

EDIT: I posted this without reading the thoughtful posts from Dan Kehn and Andy Schecter, just above in this thread. My excuse is that there was a page break and I was too lazy to go back in the thread. So, although I have said much the same as this before, going back to the original GS3 threads, I see that I am merely repeating what they have said so I defer to their analysis.

[hbuchtel]

With regards to Chris (Malachi) 's quote about the GS3, there are two different questions, right? One is whether Chris or people in general are able to distinguish such small temp differences, and the other question is how well the little glowing number represents the temp of the water hitting the puck...

It doesn't seem unreasonable for a person to be able to distinguish between slightly different temps, especially when using a blend one is familiar with. In a familiar situation we can detect quite small changes... what is missing, what is new, etc.

I would love to see a long-term blind taste testing... a year or so of a couple blind shots a day would do it

Henry

[AndyS]

That is my exactly my point: Unless it can be demonstrated in a blind taste test, such statements should be treated with skepticism on the basis of a "thought experiment" alone.

OK, we surely agree. I'd just add what I said previously: almost all the interesting and surprising stuff has been the result of real experiments. The so-called thought experiments normally add nothing more than a lot of boring, obvious commentary.

[luca]

Hey kids,

As you say Ken, these things are all a massive PITA. I have done a bunch of cuppings, blend testings, etc, but I haven't ever tried to make anything statistically significant. In that regard, I have a lot of respect for Jim and yourself.

There is a very small chance that my local LM distributor might be able to help us out on this one. I haven't asked yet, but they usually have a few machines sitting around and a swift and they're usually quite accomodating. The swift doesn't quite get the same sweetness into a shot that you would get from a Robur, but it does get you consistent shots quickly. I figure that if I could borrow a swift and something like an FB80 and a GS3 or whatever they have around, then get a few volunteers, I might be able to organise some sort of a test. Obviously it would be a very narrow test, but at least it would be something.

Thoughts?

Cheers,

Luca

[DavidMLewis]

And I'm not talking about casual tasting when looking at some sort of temperature readout, I am talking about real and verifiable shot temperature measurements with that sort of accuracy, which I think the current crop of probes and digital thermometers cannot reliably deliver on a repeatable basis.

Hi Ken,

I know, given your background, that you know this stuff, but it seems germane to review the basics and maybe be more precise in our terminology. When we're talking about something like temperature, even without getting into temporal variations during a shot or spatial variations within the puck, three things are important to distinguish: precision, accuracy, and repeatability. The first, precision, refers to how fine or coarse are the available measurements or settings. These may be different: my scale has grams on it to two digits after the decimal point, so it can display 0.01 g increments. It only does in fact display in 0.05 g increments, though, so that's its precision. Accuracy refers to how closely those measurements correlate with a standard, and in this case that's where the "current crop of probes and digital thermometers" fall down a bit. The third, which I contend is more important to the discussion, is repeatability: how closely can I get, with a given setting and ritual, to the same temperature every time? On my machine, for instance, I have no particular reason to believe that its output temperature is what Reneka tells me it is. But the probes are fast-responding RTDs, which drift slowly in their response to a given temperature. The circuitry is set by 1% metal-film resistors, which also drift slowly. And the ritual is fairly consistent because like many on this site I've learned to make OCD work for me as a vital component of my lifestyle. So if I change the temperature by what Reneka claims is 1° C, the precision, I figure it's changed by something fairly close to 1° C, even though I don't have any idea what it changed from or to (the accuracy). And when that change produces a far-from-subtle taste difference, over many SO coffees and many years, and when that taste changes less between shots than between temperature changes (the repeatability), then I conclude that I can taste a difference due to a 1° C, or so, temperature variation. Of course I can always be fooling myself, but I'd be happy to repeat the test for any H-B participant who cares to stop by my house, and over time come closer to a consensus. Note that I'm not saying anything here about the original question, which was at what point, for most people, these difference cease to become apparent or fall below the available repeatability in other aspects of pulling the shot.

Best,
David

[Ken Fox]

. . . . I conclude that I can taste a difference due to a 1° C, or so, temperature variation. Of course I can always be fooling myself, but I'd be happy to repeat the test for any H-B participant who cares to stop by my house, and over time come closer to a consensus. Note that I'm not saying anything here about the original question, which was at what point, for most people, these difference cease to become apparent or fall below the available repeatability in other aspects of pulling the shot.

Best,
David

A resolution of 1 degree Celsius is almost 2 degrees F.

Any of us who have equipment whose brew temperature we know how to adjust, has certainly had the experience of how some coffees taste differently with temperature adjustments. I myself have played around with this in the last couple of days with a particular coffee I roasted that I'm not very fond of, by changing the brew temp from about 198 to about 201F (it tasted differently, but I still didn't like it). So, I'm not doubting the thesis that brew temperature changes induce taste changes. What I'm doubting is the reliability and repeatability of this with SMALL changes, both as regards equipment limitations and the limitations of human tasting apparatus.

2 degrees F is probably a range that many or even most espresso tasters could detect, and certainly at least some of the current crop of equipment can deliver repeatable shots with that degree of temperature difference.

What I don't know is whether current equipment can reliably produce shots at repeatable temperature differences of 1 degree F. That would absolutely need to be established before any tasting studies could go forward. Assuming the equipment can do this, then one could test the potential of some tasters to detect this difference. Any brew temperature difference below 1 degree F probably cannot be accomplished with current equipment on a repeatable basis, and you'd have to count me as a doubter on that until I am proven wrong (which I'll acknowledge when I am).

ken

[Ken Fox]

Hey kids,

As you say Ken, these things are all a massive PITA. I have done a bunch of cuppings, blend testings, etc, but I haven't ever tried to make anything statistically significant. In that regard, I have a lot of respect for Jim and yourself.

There is a very small chance that my local LM distributor might be able to help us out on this one. I haven't asked yet, but they usually have a few machines sitting around and a swift and they're usually quite accomodating. The swift doesn't quite get the same sweetness into a shot that you would get from a Robur, but it does get you consistent shots quickly. I figure that if I could borrow a swift and something like an FB80 and a GS3 or whatever they have around, then get a few volunteers, I might be able to organise some sort of a test. Obviously it would be a very narrow test, but at least it would be something.

Thoughts?

Cheers,

Luca

Hi Luca,

I don't want to repeat what I typed in my response to David Lewis, so please read that response in addition to this one.

I welcome your willingness to look at this, which as you state, will not be an enjoyable experience. Before doing anything, however, I think we need to try to avoid the possibility of doing a study that gives an apparent but false result, which could happen if, say, shot curves overlap even though numerical readouts suggest high precision.

As a very first effort I would take a Scace device with a good digital datalogger and plot out, say, 25 shot curves taken at one intended temperature, then do another 25 at a temperature which you think will not produce curves overlapping with the first set. One would have to know to what degree the shot temperature curves are in fact distinct and not overlapping. My guess is that you would have to get the intended shot temp curves close to one degree C apart in order to have separation. If this is true, the hypothesis would not be worth testing because most of us would probably accept that many tasters could detect that degree of temperature difference, and you would just be "proving the obvious."

I have recently posted this set of shot curves from my old vibe Cimbali Junior:



While I did not do 25 shots at each temperature, I was just trying to establish what the degree of imprecision is, not the ability of the equipment to produce very fine temperature distinctions, which it is obvious that it CANNOT. What I can say on the basis of THIS graph is that, as I am using it, the machine can produce shots within about 1 degree F of either side of the temperature I would like to have, e.g. the shots occur within a "band" of about 1 degree C. This degree of precision is not adequate to test the hypothesis that we are discussing, e.g. the ability to produce and detect differences in shots at small incremental temperature differences.

If you can get reliable separation of the curves, without overlap of the temperatures, on the order of (say) 0.5 degree C, then the hypothesis would be worth testing and the results would be interesting.

Good luck!

ken

[Tristan]

This is an interesting thread. This discussion makes me think of a quote from an Italian humanist who lived in the 14th century named Petrarch. He said, "It's better to will the good than to know the truth." I'm not sure the truth will inspire us to make better coffee drinks.

I think sometimes dwelling too much on science can interfere with the enjoyment of the coffee. I think this is especially true if you don't have a pro-sumer set up (like me!). Still a noobie here , so I'm trying to stay as consistent as possible with my routine! Ignorance might be bliss!

This being said I would still be interested in the outcome of such a blind tasting study to determine if precise temperatures really make a significant impact on the final product. Maybe this will further the merit of higher end machines or possibly validate the use of PIDs?

[Ken Fox]

This is an interesting thread.

I would still be interested in the outcome of such a blind tasting study to determine if precise temperatures really make a significant impact on the final product. Maybe this will further the merit of higher end machines or possibly validate the use of PIDs?

I don't think there is any remaining need to "validate" the use of PIDs. If you take the most basic example, for example the use of them in a machine like a Silvia, they merely compensate for a very poor stock method of boiler temperature control on that machine, something that most would find simply unacceptable. The thermostat that comes with that machine is so poor that people have to "temperature surf" just in order to get a drinkable shot.

As to the use in more expensive machines, in lieu of a pressurestat, PIDs have obvious value that extends beyond the ability to make a "better" shot. Having PID'd my two single group Cimbali machines, I don't think I have ever claimed that having done so produces "better" shots. What I have said, and what has been said by others, is that with a PID one can better control the temperature of what is being controlled (the boiler in my machines) by eliminating the hysteresis of a pressurestat. One can also change temperatures easily, on the fly, something one cannot do with a pressurestat. Finally, pressurestats don't tend to last very long, with the typical Maters and CEMEs lasting at most 2 years. A PID installation should last a much longer time, another fairly obvious benefit.

ken

[Tristan]

I don't think there is any remaining need to "validate" the use of PIDs.

Apologies, I should chosen my words more carefully. My overall "noob-dumb" haunts me

You've sold me on the merit of PIDs! I didn't realize they had so many other benefits!

[timo888]

I apply the same layman's analysis to John's statement. The brew pressure at the top of the puck is 9 bar... and a lot less than 9 bar at the bottom of the puck. So a brew pressure spectrum varying from 9 bar to the exit brew pressure at the bottom of the puck is impacted by a 0.05 change in pressure? Yet again, intuitively I would say no.

I was under the (quite possibly mistaken) impression that pressure is a uniform continuum, and that "top and bottom of the puck" would not come into play. A loss of pressure in a closed system (e.g. a puncture in pressurized tank) causes the pressure everywhere in the system to drop. There aren't pockets or areas of differing pressure.

Perhaps Greg could interpret Illy's brew pressure equation for us lay folk? The brew pressure, IIRC, was a complex function of inlet pressure and outlet loss of pressure as the water flowed out, plus a few other variables.

Regards
Timo

[HB]

A loss of pressure in a closed system (e.g. a puncture in pressurized tank) causes the pressure everywhere in the system to drop. There aren't pockets or areas of differing pressure.

Sorry, I may be all wet. My two years of college physics was a long time ago and fluid dynamics was only a few chapters.

What you say makes sense for static (equalized) pressure like a balloon or water tank, but wouldn't a puck be more akin to an orifice? For example, if a 100' steel pipe was filled with sand and high-pressure water introduced in one end, I would expect the measured pressure against the walls of the pipe to be lower the last 10 feet of the pipe than the first 10 feet, assuming water is flowing. Wouldn't the same be true for a filter basket, on a much smaller scale?

BTW, I once had a similar discussion with my young son about a balloon and why the pressure was the same everywhere within it, even if you squeezed one side. I don't think that I convinced him. Corrections/explanations for either of us are welcome.

[ntwkgestapo]

Dan, you are correct! Just think, if the puck didn't supply varying resistance. and therefore a moderating effect to the pressure, thruout it's "length" you'd be getting espresso out of your bottomless P/F (or the spouts) @ 8-9BAR! Talk about a Portafilter SNEEZE!

[AndyS]

I was under the (quite possibly mistaken) impression that pressure is a uniform continuum, and that "top and bottom of the puck" would not come into play. A loss of pressure in a closed system (e.g. a puncture in pressurized tank) causes the pressure everywhere in the system to drop. There aren't pockets or areas of differing pressure.

If the pressure everywhere in the tank dropped uniformly, the air would have no motive force to rush to the side with the puncture, would it?

As far as the portafilter goes, the prevailing theory seems to be that there is a moderate pressure drop as you go down through the puck, and then a very severe pressure drop at the bottom where the fines accumulate.

[timo888]

If the pressure everywhere in the tank dropped uniformly, the air would have no motive force to rush to the side with the puncture, would it?

As far as the portafilter goes, the prevailing theory seems to be that there is a moderate pressure drop as you go down through the puck, and then a very severe pressure drop at the bottom where the fines accumulate.

The gas tank I suggested is probably not an accurate analogy for brew pressure in a percolation scenario. The rush of gases there is from inside to outside, since Nature loves equilibrium.

I can see that pressure would fall to atmospheric pressure where the coffee exits the filter, but I don't know how much difference in pressure there would be between the "top" of the puck, the "middle" of the puck, and the "bottom" region of the puck. It's not a very thick medium, after all. There is also what Illy calls the 'time-dependent geometry' of the puck, where migration of fines in the direction of flow towards the filter basket's perforations may be causing a damming effect lower in the puck, reducing the flow and counteracting the loss of pressure that goes hand in hand with the flow.

The pressure is quite complicated, judging from Illy's equation. There's the inlet pressure, the hydrostatic pressure, the flow of liquid through the compacted grains, and some other goings-on named after the scientists who discovered the laws. I don't have the book in front of me, but it would be interesting to have that equation teased out.

Regards
Timo

[erics]

Greetings Timo -

. . . but it would be interesting to have that equation teased out.

The "equation" (integration) you are referring to is represented by the area under the curves I pictured (from the book) in this other great post of Andy's: Playing with Pump Pressure: Parte Due

This equation simply(?) says that the area under the curves of flowrate (ml/sec) as a function of time (sec) is the volume of beverage in the cup. As I said in the aboved linked post, an integration of one of those curves yielded some unreasonable numbers for the time involved. Furthermore, the comments in the book that " But two observations that lie in clear contadiction . . ." is sorta misleading because the variation in resistance is not mentioned in the same argument.

But getting back to the original topic, certainly the ability to have repeatible temperatures (and pressures) is important. Its difficult to write about the temperatures and pressures during the extraction process because the temperature and pressure of the water presented to the puck are really the only values we have a good feel for.

[timo888]

Thanks for the link, Eric. The equation I am recalling from the Illy book had many more variables than are discussed in the thread there with respect to the interrelationship of pressure and flow. I was referring to that section of the book in this thread back in August of 2006:

Pressure on the cake does not remain constant during the percolation process, but varies as a function of the characteristics of the hydraulic circuit above the cake. This can be verified by continual pressure sensors: the recordings yield a function p = p(t) which exhibits an initial transient rise, increasing more or less slowly. The dry bed still lacks adequate cohesion and is susceptible to resettlement; therefore the initial phase appears to be decisive in percolation. After wetting, ground coffee particles swell up firmly interpenetrating each other, and percolation can follow its stationary course. This effect explains why...the flow is not constant during percolation, rather showing an 'asymptotic flow dependency'. .... Hydrodynamic experiments demonstrate that the average flow ceases to depend linearly on pressure in the proximity of 9 atmospheres and that an increase in pressure actually causes a decrease in the average flow....

Regards
Timo

[erics]

Timo -

We are referring to the same "equation" as the graphs I posted from the book describe your quote from Illy. I am referring to the 2nd edition in which Chapter 7 has the information you are referring to in Chapter 8.

If you don't have the book handy, you can fo a "google" on 'Espresso the Science of Quality' and Amazon will let you search the pages for "pressure." Send me an email at erics@erols.com and I will send you my explanation of the equation as it is beyond the scope of this topic.

[bernie]

Has any work been done on the relative importance of other variables in brewing espresso which is as precise as the temperature studies we have seen? I ask because it appears at first blush that the degree (pun intended) to which temperature studies are beaten somewhat exceeds the degree to which they impact the results of the studies given the lack of work on other variables. The first thing that comes to mind is the effect of the exposure of the dry puck to the heat of the group head once the pf is locked. At what point does the difference in one degree F. increments become less of an impact than that dwell-time? If I look at it in terms of percentages the difference between 199F and 200F is one-half of a percent. But if you look at the dwell time of exposing the dry puck to the group head of just a couple of seconds the difference can be 200 percent. Is exposing the puck to a temp of 200F for twice the amount of time as important to consider as one-half percent difference in temperature? It seems so to me. Just looking at .5 and 200 makes me think it is becoming more important the more we drill down on the temp studies.
Bernie