It depends on how big the change is and even more important, how big the machine is. Since we were discussing a commercial environment, I assumed big multi group which is a world of difference from a Brewtus, La Spaz. The brew boiler on a three group is quite large. For the machine to stabilize, it takes some time. That goes beyond just the boiler changing temperature, but the entire machine (all 150 or so pounds of steel) to adjust to the new temperature. On a home machine, the change is much quicker but still needs, I would guess, twenty minutes to stabilize after a 2 degree change. Whether the change was up in temperature or down in temperature would also have a part. I believe a machine gives up heat faster than it will take heat so cooling down would happen faster than heating up, but I have no proof of that, just a theory.

Cup taste, I can't explain it. Some machines just make a cleaner cup. The VBM Domobar Super makes a little cleaner cup than the Isomac millennium, yet they are both E61 vibe pump machines, the Elektra Microcasa leva pulls a dramatically different shot than a (insert lever machine name here). Why? They are both single boiler spring assist but the shots are worlds apart, can't explain it. Things like the length of tubing in the machine, diameter of tubing, heat exchanger size/water steam ratio, shower screen, dispersion block, headspace, pump type, I am sure all play a part.

cannonfodder wrote: I believe a machine gives up heat faster than it will take heat so cooling down would happen faster than heating up, but I have no proof of that, just a theory.

The fact that my Brewtus heats up in 40 minutes or so and is still warm hours after I shut it off makes me think it would actually take much less to heat up a degree than to cool down a degree, though the cool down could likely be helped by just flushing a large bit of water.

Ira

Yeah, but now you are treating it like a heat exchanger

LeoZ wrote:this post hits on my 2 biggest flaws of an HX.
water use, and heat.

Some generalizations about HX machines are valid, but each model has its own characteristics. My experience with HX machines is markedly different than yours. I have never had to flush more than 4oz on my Vetrano, and 2-3oz is typical. And that's with a pstat setting of 1.3bar.

Ditto the heat issue, which is directly responsible for your increasingly large flushes. The water in your Giotto tank slowly heats up over time, requiring greater flush volumes. One advantage of a direct plumb machine is that the incoming water is always cool, so I don't have this problem. Consider insulating the boiler; that should help with overheating issues.

Note that a small flush (1-2oz) is typical on DB machines. Heating two boilers will generally consume more electricity (and generate more heat) than one boiler. So although HX machines will waste a bit more water, all other things being equal, the energy requirements should be less.

LeoZ wrote:how different a drink will a double boiler produce? why would using more than one blend matter for a double boiler?

Brew temperature management is fundamentally easier on DB machines, especially if your goal is a flat brew temperature profile. On a DB, you set the brew temp, flush 1-2oz to warm the brew group, and pull your shot. Is the brew temp profile flat? Well, no... it's going to drop initially when it hits the cooler coffee grinds in the puck, then gradually rise. But at least the water hitting the puck should be at a constant temp. With an HX, you're much more likely to see changing brew temps throughout the shot.

Which is better? Amazingly enough, nobody appears to have done a seminal study comparing the effect of flat vs. variable brew temps on taste. Until then, it's anyone's guess.

shadowfax wrote:Yeah, but now you are treating it like a heat exchanger

Not really, just trying to get rid of some of the heat when lowering the temperature. I only flush an ounce or so to warm up the cup and as I essentially never adjust the temperature I never had to worry about that, but if I was in a hurry it seems like that would be a possible solution.

Ira

Ira: Yeah, I was just messing with you.

Personally, I would say that for nerds like us, HX vs. DB is a personal preference issue (and sometimes a personal finance issue). I have been very amused to read posts by various people praising Slant-L vs. HX hump, people arguing that temperature stability within the shot is necessary, and others arguing that some variation actually improves the cup. What I have personally gleaned is that both HXes and DBs have advantages and disadvantages, and, as Dave mentioned, there's really not even a lot of consistency of results with in each class--there's a pretty wide variation in the cup between extremely similar consumer grade E61 machines, not to even mention a comparison between, say, a QM Vetrano and a Cimbali Junior/Elektra A3--both of which I think a lot of people would say would kick the pants off of Brewtus. Things might get more heated vs. a GS3 or a Mistral.

I didn't really intend to bring those issues up in this thread so much as the usability issues for people who aren't familiar with the inner workings of an espresso machine. I have to admit that I think I would feel a lot more comfortable making drinks on a big DB (which I have never done) vs. a big HX machine (which I have done). I feel somewhat unsure about how well I could flush to get consistent brew temperatures over a spotty usage profile. On the other hand, I think I would be at home with either machine after spending a lot of time with it.

There's definitely something to be said for Randy's argument. On the one hand, I think that designing things that are as easy to use as possible is important, and I would say that DB machines are simpler to use in general. On the other hand, the barista's job is to know his/her machine and make you a proper drink on it, and it's not unreasonable to expect them to be trained to flush. Just like cleaning their machines.

cannonfodder wrote:Cup taste, I can't explain it. Some machines just make a cleaner cup. The VBM Domobar Super makes a little cleaner cup than the Isomac millennium, yet they are both E61 vibe pump machines, the Elektra Microcasa leva pulls a dramatically different shot than a (insert lever machine name here). Why? They are both single boiler spring assist but the shots are worlds apart, can't explain it. Things like the length of tubing in the machine, diameter of tubing, heat exchanger size/water steam ratio, shower screen, dispersion block, headspace, pump type, I am sure all play a part.

having the mcal and the giotto, i agree. there are inherent differences in machines. all of the items you point out are things that a manufacturer would consider in design and output. (just as in other commercial machines, chillers for example, in my engineering background).

its interesting that taste would be the final, differing variable, especially since the end result of tweaking, measuring and identifying becomes as close as we can get to a steady state, or predictable temperature and pressure profile.

when i bought the mcal, i told my wife id make a decision b/t it and the giotto, and sell the other. a year later, both remain, because both are so unique.
so, now that im dying to see the new VB DB (cant decide, HX, DB, rotary?) machine.. whats next?! oy vey..

anyway, while the design of an HX is ingenious (im sure ive said this before) it just seems wasteful.

everyone here has pointed out the ability to control temperature (and thus taste) on an hx.\

speaking of temp, its my understanding that with brewed coffee, a spot on, consistent temp is most desired.
cross that theory over to a thermoblock espresso machine, and it attempts to duplicate this theory. enter the world of HX, and everyone claims the superior taste of a shot that has varying temp changes, allowing the flavors to be extracted across many profiles.

RapidCoffee wrote:Some generalizations about HX machines are valid, but each model has its own characteristics. My experience with HX machines is markedly different than yours. I have never had to flush more than 4oz on my Vetrano, and 2-3oz is typical. And that's with a pstat setting of 1.3bar.

thats odd. do you leave your machine on long? over weekends, or weeks i know im working from home or nearby, ive kept it on for up to a week straight.
ive reduced my boilers as low as .6 bar, but steaming sucked. its at .9 now. still gets hot. guess its just a hot machine. lol

Which is better? Amazingly enough, nobody appears to have done a seminal study comparing the effect of flat vs. variable brew temps on taste. Until then, it's anyone's guess.

thats even more odd.
all the graphs, tests, profiles, and no in the cup results.
we need more art, and less science.

LeoZ wrote:thats odd. do you leave your machine on long? over weekends, or weeks i know im working from home or nearby, ive kept it on for up to a week straight.

Like you, I turn off the water when I brush my teeth... and turn off my espresso machine when it's not going to be used within the next few hours (e.g., when I leave for work in the morning, and when I go to bed at night). But even when the Vetrano has been on for several hours, an insulated boiler and cold input water supply keep overheating problems at bay.

LeoZ wrote:thats even more odd.
all the graphs, tests, profiles, and no in the cup results.
we need more art, and less science.

I'd say we need more of both - but especially more science. Taste tests have little scientific validity unless they're done properly: double blind with statistically significant sample sizes. Most folks on coffee forums (including yours truly ) conveniently ignore these issues when doing taste tests.

RapidCoffee wrote:I'd say we need more of both - but especially more science. Taste tests have little scientific validity unless they're done properly: double blind with statistically significant sample sizes. Most folks on coffee forums (including yours truly ) conveniently ignore these issues when doing taste tests.

all a double blind in espresso taste tests would do is slow the barista down. without knowing the beans, the barista would have to take that many more shots to adjust for the unknown.
whats wrong with a single blind? or, less complicated, just tasting shots from the 2 machine types! sounds like that hasnt even been done based on your comment above.