HX versus Dual Boiler: I TAKE IT BACK!

[miKe mcKoffee]

Ya know, I've changed my mind. All else being equal, regardless if routinely changing shot temps between shots in series of shots, I'd no longer recommend HX over Dual Boiler for HX convenience of calling shot via flush & go or flush & wait. Flush the flash! What was I thinking! Dual Boiler more intra shot stable than HX and obviously easier to do a series same shots same temp. So what if lowering DB shot temp might be a bit slower than HX flush & go to get lower temp, reality is not that slower if using a flush the DB to lower temp then wait for it to come back up! It took forever flushing both group and steam boilers simultaneously on Barry's Brute simply because the HX boiler inlet water was/is too high, duh.

Now if between direct plumbed rotary HX versus tank vibe DB, it's maybe a tougher choice. But since tanks easily converted to auto-fill throw that out too. So it'd really only be rotary HX versus vibe DB. Then there's vibe to rotary conversion, or S1... (I won't bother mentioning GS3) Seems to me now, upon mucho further reflection, if DB in the budget that's the way to go. Period. End of story.

My apologies if I previously led anyone astray. I still love my Bric', just not as much. Part of this realization came last Saturday during the Gathering. HX flash flush & go required stopping myself or someone else mid-conversation more than once to hear the flash to count for the temp, how rude of the Bric'!

[Ken Fox]

Ya know, I've changed my mind. All else being equal, regardless if routinely changing shot temps between shots in series of shots, I'd no longer recommend HX over Dual Boiler for HX convenience of calling shot via flush & go or flush & wait. Flush the flash! What was I thinking! Dual Boiler more intra shot stable than HX and obviously easier to do a series same shots same temp. So what if lowering DB shot temp might be a bit slower than HX flush & go to get lower temp, reality is not that slower if using a flush the DB to lower temp then wait for it to come back up! It took forever flushing both group and steam boilers simultaneously on Barry's Brute simply because the HX boiler inlet water was/is too high, duh.

Now if between direct plumbed rotary HX versus tank vibe DB, it's maybe a tougher choice. But since tanks easily converted to auto-fill throw that out too. So it'd really only be rotary HX versus vibe DB. Then there's vibe to rotary conversion, or S1... (I won't bother mentioning GS3) Seems to me now, upon mucho further reflection, if DB in the budget that's the way to go. Period. End of story.

My apologies if I previously led anyone astray. I still love my Bric', just not as much. Part of this realization came last Saturday during the Gathering. HX flash flush & go required stopping myself or someone else mid-conversation more than once to hear the flash to count for the temp, how rude of the Bric'!

OK, I'll take the bait.

Double boilers require a flush as well, at least all of them save (maybe) the GS3 and maybe the Synesso. The Aurelia turned heads at the SCAA this year for its extreme temperature stability, yet it is a HX machine. No one has established (to my knowledge) exactly how much temperature stability is needed (from shot to shot) before the taste difference is detectable; the home enthusiast whose taste I probably most admire tells me he needs 2 degrees CELSIUS differences in shot temperature before HE can taste the difference. I'm convinced I can taste the difference between 198F and 203, but I'm not sure if I can detect differences of less than that.

Shot profile temps (e.g. the way the SHAPE of the curve interacts with the taste) is a whole different matter. I know of no good studies that show that a flat line shot temperature curve is better than a humped curve as one finds on some heat exchangers.

Intershot temperature stability is very hard to obtain; it is possible with mods to limit the variability considerably on at least some heat exchanger machines with fairly simply techniques such as temp surfing or using a PID. Double boilers are not immune from these problems except *perhaps* if you are willing to spend $4500 or $6000+, amounts beyond the reach or the common sense of most home enthusiasts.

In summary, I wouldn't try to tell someone else what they should buy, and I'm not recommending any particular machine or type of machine to anyone, but I am unconvinced that double boilers are inherently preferable to the vast majority of home users planning to buy a machine with reasonable prices in 2006.

ken

[RapidCoffee]

In addition to Ken's excellent arguments, let me add one more. AFAIK there is not a single controlled study - not one - that clearly shows DBs make better espresso than HX machines. Granted, it's easier for a noobie to reproducibly hit a specific brew temp on a DB. Does this make DBs better? Not necessarily.

I'm perfectly willing to be convinced that DBs provide superior technology. But I'd like to see some compelling evidence before I rush out to buy a new espresso machine.

Still enjoying my HX - John

[cpl593h]

While I've not really had much experience with HX machines, more and more I'm realizing the negative effects of feeding an e61 thermosyphon with brew temperature water.

And double boilers do require a flush - to clear out the cooler water in the thermosyphon loop - you just don't have to listen for anything.

[Matthew Brinski]

Can you really perform a "controlled study" between a HX and DB looking for the better espresso when the results are evaluated with taste? If someone wants a definitive test, I think it's going to be a long wait.

Also, if the temp difference can't be detected within 2 degrees Celsius, doesn't that negate the argument of "HX curve profile versus flat profile" since the hx intrashot differences are usually within 2 degrees Celsius (at least the readings on my Vetrano)?

For me it comes down to predictable and repeatable brew temps. Eventually it will be "Goodbye Vetrano, hello GS3 or Synesso".

Matthew Brinski

[Ken Fox]

Can you really perform a "controlled study" between a HX and DB looking for the better espresso when the results are evaluated with taste? If someone wants a definitive test, I think it's going to be a long wait.

yes. Jim Schulman and I have done 2 different blind tasting experiments over the last several years using my two Cimbali Juniors, one an old vibe and one a new rotary. The barista pulls the two shots simultaneously, the taster has his back to the machines sitting down at a table, the two shots are delivered at the same time, and the taster does not know which is which but the barista does. Simple. You have to do a whole bunch of shots like that to have any chance of detecting differences. If you did 30 or 50 pairs like that and if there was no tendency to prefer the shots from one machine over another, you could assume that there certainly wasn't any huge difference. There is of course also the unpleasant fact that shots vary on their own for no particular reason that the home barista can put his finger on, so unless the machine produced shots that were sufficiently better to rise above this background shot quality variation, then any improvement, real or imagined, could get lost in the mix.

You could subject the data to standard statistical tests, as Jim has done with our data. This is science and generally considered more valid than deciding that "X" is better than "Y" because you think or hope it is so.

Also, if the temp difference can't be detected within 2 degrees Celsius, doesn't that negate the argument of "HX curve profile versus flat profile" since the hx intrashot differences are usually within 2 degrees Celsius (at least the readings on my Vetrano)?

I don't know what the taste threshold for temperature differences is for the average home espresso enthusiast. I don't know how one could know that without some sort of blind tasting experiment which could be done along the lines as above. And I don't have any data to agree or disagree with the idea that shots made with flat profiles might taste different than shots made with humped profiles and how many degrees are important in that situation.

For me it comes down to predictable and repeatable brew temps. Eventually it will be "Goodbye Vetrano, hello GS3 or Synesso".

Matthew Brinski

I think you should buy whatever you want to buy, and I hope you are happy with it, just don't believe you are acting based upon any sort of accepted knowledge, because you aren't.

ken

[AndyS]

the home enthusiast whose taste I probably most admire tells me he needs 2 degrees CELSIUS differences in shot temperature before HE can taste the difference. I'm convinced I can taste the difference between 198F and 203, but I'm not sure if I can detect differences of less than that.

Shot profile temps (e.g. the way the SHAPE of the curve interacts with the taste) is a whole different matter. I know of no good studies that show that a flat line shot temperature curve is better than a humped curve as one finds on some heat exchangers.

(1) Sensitivity to temperature is apparently very blend-dependent. Schomer, who popularized the precise temperature craze in the US, uses a blend with lots of monsooned malabar. The MM is reputed to be very fickle (temperature-wise) in espresso.

(2) Since HX machines generally have a profile that slides through a range of several degrees, it is possible that the effect of small changes in the average temperature of the curve are lost. A machine with a flat profile might make small temperature adjustments more obvious in the cup. Or not. There isn't much data. Chris Tacy swore his blind tasters could discern 0.3F changes when brewed on the GS3.

[Ken Fox]

(1) Sensitivity to temperature is apparently very blend-dependent. Schomer, who popularized the precise temperature craze in the US, uses a blend with lots of monsooned malabar. The MM is reputed to be very fickle (temperature-wise) in espresso.

(2) Since HX machines generally have a profile that slides through a range of several degrees, it is possible that the effect of small changes in the average temperature of the curve are lost. A machine with a flat profile might make small temperature adjustments more obvious in the cup. Or not. There isn't much data. Chris Tacy swore his blind tasters could discern 0.3F changes when brewed on the GS3.

Hey Andy,

I don't think that Chris Tacy spoke of blind tasting 0.3 degree changes. As I recall his comments, he had taken the machine to a beach house and he and others using the machine, looking at the digital readout, thought they could notice such differences. That is worlds away from blind tasting confirmation and in my opinion, beyond the capacity of the human tasting apparatus except as a very rare mutation.

As to the temperature specificity of MM, there are of course people who don't like it regardless of temperature.

ken

[luca]

Interesting thread. A few thoughts ...

I think that all HXs are not created equal and all DBs are not created equal, so I really don't think that generalisations like 'HXs are better/worse/equal to DBs' are really all that helpful. For example, the Synesso that we're using at the moment is worlds better than the grungy, beat up Linea that we borrowed whilst waiting for it. (Old, in poor repair, failing thermostat and no preinfusion) In turn, that Linea was unbelievably sucky compared to some of the uber-hotrodded lineas that I have used. In terms of HXs, I used to use an Azkoyen that required heaps of TLC to get really good shots out of. In comparison, I have played on an uber-tweaked Wega that made making great espresso like shooting fish in a barrel - presumably using a NS Aurelia would be similar. I could go on and on ... (but I freely admit that my experience with prosumer machines isn't as wide) Unfortunately, though, this means that, IMHO, the best advice for prospective buyers remains try it if at all possible.

With regards to temperature differences, part of my cafe job at the moment has involved picking up a kilo or two of interesting coffee for us and any coffeegeeks who want to drop by on the weekend. This weekend we've got a great blend from a boutique roaster who's a great inspiration to us. We started off at 201F and the espresso had an interesting spicy and savoury taste. It was good; different, but we were kind of scratching our heads a bit. So we dialled it up to 202 and it became noticeably sweeter and more well rounded. At the end of the day, when we were closing up, we had a green buyer/roaster drop by, so we gave him a shot at 201.5F, which he thought was pretty good. We were still curious to see what taking the temp just a notch higher would do, so we bumped the group up to 203 and made a double espresso latte for our roaster and some espressi for ourselves. He humoured us by taking a sip and, even through the milk, noted a clear change, describing the espresso as 'wild' - we thought that it had gotten too acidic at that temperature. As he was leaving, he asked us what we had done to change the second shots and was surprised when we said that we had only bumped the temp up 1.5F. Now, I'm not going to pretend that all of my shots were exactly the same speed and length, but, visually, they looked very, very close to me and from similar experiments over the past few months I did have an idea of how to fudge the temperature to change the flavour profile.

Can you really perform a "controlled study" between a HX and DB looking for the better espresso when the results are evaluated with taste? If someone wants a definitive test, I think it's going to be a long wait.

Dan did an excellent job of this in his Buyer's Guide to the La Cimbali Junior ... but, then again, the Junior isn't one of the e-61 box tribe ...

These sorts of tests are logistically really difficult to do. We found that this was the case when we were trying to compare the giotto to the brewtus.

Cheers,

Luca

[AndyS]

I don't think that Chris Tacy spoke of blind tasting 0.3 degree changes. As I recall his comments, he had taken the machine to a beach house

Ken, I know you prepare your espresso at relatively high altitude. Understandably, it is hard for you to comprehend that meaningful espresso comparisons can, in fact, be done at low altitudes, ie, at a beach house.

he and others using the machine, looking at the digital readout, thought they could notice such differences. That is worlds away from blind tasting confirmation

Chris didn't specify his testing procedure in detail, but I have a hard time believing that he would have been so sloppy as to publish this data if his tasters were looking at the readout.

The difference is taste with the Vivace Dolce at 203.0F and 203.3F was truly dramatic (from marginally drinkable to really, really good).

<snip>

small changes to brew temp were immediately discernible to even untrained palates. At one point, the Stumptown semi-regular said, "this espresso tastes different - sharper in some way - what happened?" after a reduction of 0.3F.

And he presented some data here.

I agree with the point that you're making, of course, that without detailed notes about the testing procedure, and without others being able to replicate the results, these results are far from conclusive.

And I remain somewhat mystified at this data, since the GS3 prototypes that both Greg Scace and I received could be set to 0.3F intervals, but the machines couldn't deliver brew temperatures with that accuracy. Chris's machine would have had to be a lot better than ours.

[HB]

Since HX machines generally have a profile that slides through a range of several degrees, it is possible that the effect of small changes in the average temperature of the curve are lost. A machine with a flat profile might make small temperature adjustments more obvious in the cup.

It makes sense that a double boiler has the advantage of reproducibility compared to an HX machine, which relies more on the operator. But the notion of a "flat profile" seems more and more like a myth to me:


One of these four curves was from a double boiler espresso machine... which one?

Many who hear "flat temperature profile" likely assume that it means just that, i.e., except for the first few seconds, the coffee puck experiences the same extraction and brew temperatures throughout. In reality, the temperature from the top of the puck to the bottom doesn't converge until the last seconds of the extraction, and of course the brew pressure spans the range of 9 bar at the top of the basket to atmospheric pressure at the exit.

And I remain somewhat mystified at this data, since the GS3 prototypes that both Greg Scace and I received could be set to 0.3F intervals, but the machines couldn't deliver brew temperatures with that accuracy.

If there is a discernable taste difference between HX and double boiler machines, detecting it will hinge on the brew temperature reproducibility shot-to-shot, not a mythical superiority of one boiler output temperature versus another. As you and Greg noted, even the acclaimed performance of the GS3 indicates we're not there yet.

A matchup of Ken's PID'd Cimbali Junior and a GS3 under controlled conditions would be interesting though...

[AndyS]

the notion of a "flat profile" seems more and more like a myth to me.

Many who hear "flat temperature profile" likely assume that it means just that, i.e., except for the first few seconds, the coffee puck experiences the same extraction and brew temperatures throughout. In reality, the temperature from the top of the puck to the bottom doesn't converge until the last seconds of the extraction

Dan, we're going over old ground here. As you know, the notion that a "flat" profile is truly flat in the portafilter has been questioned for years.

This still doesn't mean that different water delivery temperature profiles don't produce different results in the cup. We just can't get around the fact that real experiments must be done to prove or disprove the various theories. Presumably there are Italian espresso researchers who have explored this in detail, but as usual, they don't offer anything more than, "We are experts, buy our machine."

[HB]

Dan, we're going over old ground here. As you know, the notion that a "flat" profile is truly flat in the portafilter has been questioned for years.

Thanks Andy for the historical reference, however my comment was meant for those without the years of experience you have. My concern is that the term "flat temperature profile" suffers a popular misconception. I obviously believe that different water delivery temperature profiles can produce different results, as I documented in HX Love. Getting from believing something is true to demonstrating to others it's true isn't easy. In the case of the question of humped versus flat temperature profiles, I'm not motivated to exert the considerable effort to "prove it" since I was convinced long ago.

Now if I had your GS3 and Ken's PID'd Cimbali Junior handy, it'd be another story...

[AndyS]

Getting from believing something is true to demonstrating to others it's true isn't easy. In the case of the question of humped versus flat temperature profiles, I'm not motivated to exert the considerable effort to "prove it" since I was convinced long ago.

I hear 'ya, running good experiments is a hell of a lot of work.

Now if I had your GS3 and Ken's PID'd Cimbali Junior handy, it'd be another story...

Hmmm...I wish I had "my" GS3, too. Unfortunately, I had to send it back to La Marzocco months ago. <sob>

[Matthew Brinski]

I think you should buy whatever you want to buy, and I hope you are happy with it, just don't believe you are acting based upon any sort of accepted knowledge, because you aren't.

ken

That is somewhat of my point. I don't think that in choosing a DB that I would be acting on accepted knowledge, and if it were accepted knowledge, how conclusive would it be? I am familiar with your's and Jim's tests regarding vibe vs rotary and preinfusion. I've read it several times in the past. It's was a great effort, and it was performed in a controlled manner. My opinion is directed toward the statement of a "controlled test" concluding "BETTER" espresso - different? ... yes, better? ... I don't think that can be conclusive due to it's subjective evaluation. With your preinfusion evaluation, you and Jim both agreed that there were detectable differences, but based on your data set, the preferences between you and Jim for which were "better" don't correlate - at least this is how I read it. Please correct me or clarify if I am in error.

So, my choosing of a DB is based on my perceived easier reproducability of a desired temp. (and I also dig the stainless on the GS3 and Synesso)

Respectfully,

Matthew Brinski

[Ken Fox]

And he presented some data here.

That isn't data; those are tasting notes.

ken

[Ken Fox]

That is somewhat of my point. I don't think that in choosing a DB that I would be acting on accepted knowledge, and if it were accepted knowledge, how conclusive would it be? I am familiar with your's and Jim's tests regarding vibe vs rotary and preinfusion. I've read it several times in the past. It's was a great effort, and it was performed in a controlled manner. My opinion is directed toward the statement of a "controlled test" concluding "BETTER" espresso - different? ... yes, better? ... I don't think that can be conclusive due to it's subjective evaluation. With your preinfusion evaluation, you and Jim both agreed that there were detectable differences, but based on your data set, the preferences between you and Jim for which were "better" don't correlate - at least this is how I read it. Please correct me or clarify if I am in error.

So, my choosing of a DB is based on my perceived easier reproducability of a desired temp. (and I also dig the stainless on the GS3 and Synesso)

Respectfully,

Matthew Brinski

In our first blind tasting test, a few years back, there was no systematic difference between rotary and vibe machines for either Jim or I. In the more recent test we did a lot of shots but used several different coffees. I had a systematic preference for the VIBE; Jim preferred the rotary but not to the same extent and once preinfusion got thrown in the whole thing got very "muddy." In the greater scheme of things there wasn't a whole lot of difference between the vibe and the rotary if you preinfuse and hence eliminate most of the sink shots.

I don't see it as a definitive study in the sense that if you had 1000 data sets from 25 tasters, you would have a much greater probability of finding small but real differences. BUT, I do think that this and the first study more or less eliminate the possibility that there is a substantial difference that would rise above "background noise," i.e. shot to shot quality variation. On this basis I feel comfortable saying that if you are thinking about trading in your vibe machine for a rotary machine, thinking that your shots will improve, they will probably not perceptibly improve on the basis of the pump.

Getting back to an *unpleasant* point I'm fond of making, if you start out with a good semi commercial machine and upgrade further, you are unlikely to even come close to the improvement you could get from using better coffee such as by improving your home roasting skills or buying from a better roaster.

ken

[gscace]

In our first blind tasting test, a few years back, there was no systematic difference between rotary and vibe machines for either Jim or I. In the more recent test we did a lot of shots but used several different coffees. I had a systematic preference for the VIBE; Jim preferred the rotary but not to the same extent and once preinfusion got thrown in the whole thing got very "muddy." In the greater scheme of things there wasn't a whole lot of difference between the vibe and the rotary if you preinfuse and hence eliminate most of the sink shots.

I don't see it as a definitive study in the sense that if you had 1000 data sets from 25 tasters, you would have a much greater probability of finding small but real differences. BUT, I do think that this and the first study more or less eliminate the possibility that there is a substantial difference that would rise above "background noise," i.e. shot to shot quality variation. On this basis I feel comfortable saying that if you are thinking about trading in your vibe machine for a rotary machine, thinking that your shots will improve, they will probably not perceptibly improve on the basis of the pump.

Getting back to an *unpleasant* point I'm fond of making, if you start out with a good semi commercial machine and upgrade further, you are unlikely to even come close to the improvement you could get from using better coffee such as by improving your home roasting skills or buying from a better roaster.

ken

Yup. Gotta have good raw materials first!!! Once you've got that sussed, then arguments about temperature, pressure, preinfusion may be posed. I've written plenty about machinery and I ain't gonna waste a lot of pages on it. but I've plenty of experience with LM Lineas, GS3 prototype, and e-61 style hx machines. I can make good coffee with all of em. It's more work to do so, and less consistent from my e-61 style machine. My hot rodded Linea produces shot after shot without my having to think about anything other than the grind fineness and raw materials. The GS3 requires similar non-thinking skills. Beyond that I ain't wasting my fingers typing except to say that folks are welcome to pull shots on my linea as long as I have some advance notice. I'm in the DC area, in the Bucolic Montgomery County Agricultural Reserve, here in luvly Maryland.

Gscace at earthlink dot net or gscace at nist dot gov.

-Greg

[Ken Fox]

Yup. Gotta have good raw materials first!!! Once you've got that sussed, then arguments about temperature, pressure, preinfusion may be posed. I've written plenty about machinery and I ain't gonna waste a lot of pages on it. but I've plenty of experience with LM Lineas, GS3 prototype, and e-61 style hx machines. I can make good coffee with all of em. It's more work to do so, and less consistent from my e-61 style machine. My hot rodded Linea produces shot after shot without my having to think about anything other than the grind fineness and raw materials. The GS3 requires similar non-thinking skills. Beyond that I ain't wasting my fingers typing except to say that folks are welcome to pull shots on my linea as long as I have some advance notice. I'm in the DC area, in the Bucolic Montgomery County Agricultural Reserve, here in luvly Maryland.

Gscace at earthlink dot net or gscace at nist dot gov.

-Greg

This is something that gets lost in all the machine, pump type/pressure, and temperature discussions. An experienced home barista will learn how to make good shots out of whatever equipment they have so long as that equipment meets a certain minimum standard. The benefit of any particular type of equipment follows the general pattern for quality one sees in all sorts of things. It's a lot like wine, where (using Robert Parker's 100 point scale) you can buy an 88 point wine for $12, a 90 point wine for $25, a 95 point wine for $150, and a 100 point wine for $450. In this analogy the Silvia/Rocky or Gaggia/Rocky is the 88 point wine and a cheap home HX/e-61 plus MM is the 90 pointer. As you get into the higher price/quality reaches, other things become more important that could be overlooked before. Using the wine analogy again, that might include whether you rinsed the wine glasses out with water after you ran them through the dishwasher to get rid of any residual detergent.

Some of the people who are the most interested in coffee (the raw materials) do not appear to put that much emphasis on equipment; I'm including people like Jim Schulman and Bob Yellin in this group. That has got to tell you something.

ken