Stainless steel vs. copper boilers

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joegsapp

Postby joegsapp » Apr 18, 2013, 9:13 pm

Hello, all,

I PMd a knowledgeable user here on home-barista with a question, and he suggested I post it in the forums for discussion.

For the years before I had a decent semi-auto machine, I could swear that I noticed an immediate difference in shots pulled from a Synesso or GS/3, regardless of cafe/location, technique, quality, etc. (i.e., when I would visit various cafes). At first, I was not sure of what I was noticing. I would have described it as a purity or clarity to the shot, or water used for the shot. It was somehow clean. I realized I never noticed this phenomenon with other machines, even with professional water filtration systems. (And this is basically true to this day) And, this over the course of 7+ years, deliberately visiting 50+ cafes, etc.

As I accumulated knowledge on machines, I realized that the Synesso and GS/3 machine are distinct from most others in that they have stainless boilers (as many of you know). Owning both copper and stainless cookware, I was immediately reminded of the ease with which wet copper imparts odor to surfaces. My copper boiler machine (Alex Duetto II) imparts a similar copper flavor to the water (though mild, it is deep in flavor).

I had concluded that it must be in the extensive use of stainless in the Synesso and GS/3 that is largely responsible for the clarity in the cup, even with poorly pulled shots. But, I cannot seem to find explicit mention of this connection in blogs such as this one.

So, now I am a bit confused. I was hoping that people with experience on machines with copper and stainless boilers (especially GS/3 owners who previously owned copper boiler machines) might lead to some clarification on my question.

Thanks in advance for your thoughts!

joegsapp

Postby joegsapp » Apr 18, 2013, 11:02 pm

...and just to clarify: I have come across the other threads on home-barista discussing the difference in flavor some people perceive before vs after flushing their boilers and/or the reservoir, and the related dual-boiler vs heat exchanger discussions. I have done many tastings of water before vs after flushes, and even water directly from the reservoir after sitting ~24 hours. Also shots (i.e., not just water) before/after flushes. That there is a taste imparted onto the water seems plain to me. That the taste may not be as evident/is different in a stainless boiler machine is more my curiosity.

john_ertw

Postby john_ertw » Apr 19, 2013, 6:42 am

Not really answering your question, but I remember reading threads where people were bashing the Breville dual boiler for using stainless boilers. If I recall correctly the reason was that the traditional Italian machines use copper boilers.

Ignoring the taste difference (if any) will stainless stand up to descaling chemicals better than copper? You read about the blue tinged water from descaling copper, but I'm not sure if descaling will cause any corrosion of stainless.

dkny3939

Postby dkny3939 » Apr 19, 2013, 7:35 am

Copper has higher heat capacity, meaning it will hold more heat and result in more stable water temp, however, copper also has higher conductivity, it will probably radiate heat away at a higher rate. In any case, copper is probably better, but I think proper insulation of boilers will make bigger difference than steel vs copper.

bobmccarthy

Postby bobmccarthy » Apr 19, 2013, 7:54 am

john_ertw wrote:Not really answering your question, but I remember reading threads where people were bashing the Breville dual boiler for using stainless boilers. If I recall correctly the reason was that the traditional Italian machines use copper boilers.

Ignoring the taste difference (if any) will stainless stand up to descaling chemicals better than copper? You read about the blue tinged water from descaling copper, but I'm not sure if descaling will cause any corrosion of stainless.



The Breville boiler question is not so much that the material is stainless, but that the steam boiler has no outlet other than steam.

Most machines have the hot water tap connected to the steam boiler so that one can change out the water by draining a portion of the boiler occasionally. The Breville uncommonly has the hot tap connected to the brew boiler. Yes you dont get hot water flash boiling when you draw water, but since steam is a distilling process all the gunk in your water remains behind. Over time it has to be pretty bad, with scale buildup and metals and other minerals in the water just concentrating. A real flaw to me and why I dont recommend it to anyone, in spite of great spec's and a very low price for the capability one gets.

bob

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another_jim
Team HB

Postby another_jim » Apr 19, 2013, 8:06 am

The problem is with testing the thesis that "steel tastes cleaner" -- it would require building identical machines except using copper boilers in one and steel in the other.

That being said, I believe there are reasons to doubt this thesis in many instances. Most traditional machines are HXs. The HX needs to be copper since it needs to absorb heat from the boiler, but water spends very little time in it, a few seconds at most to reach the group. When HXs were introduced in the early 1960s, they were advertised as providing cleaner water than the boiler water that was used previously for coffee. It could be that double boiler manufacturers went to steel brew boilers for this very reason.
Jim Schulman

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Carneiro
Supporter ♡

Postby Carneiro » Apr 19, 2013, 8:08 am

I don't think Joe is wondering about thermal differences from SS, copper and brass. If I understand he's asking about taste.

Some times I drink espressos from La Marzocco GS/3 or Strada at the importer show room. Just another day I went to the company that has a Kees Spirit waiting for the Brazilian certification, and I confess that those machines, all SS boilers and groups in general excels others I used.

But, the group and dispersion screen of each machine are different... I wonder if a E61 machine with tradicional copper boiler/HX will differ from a SS boiler/HX (new ECM for instance). The only copper part would be the pipes (but it could be SS) and the group is brass...

These days I'm using the Faema Velox I restored, and the little boiler is brass, big heat element is copper. The water always come out with a distinct smell, and if I flush 2-3 times the boiler size, it gets better, but I don't know how much it would improve with something more inert. Just for comparison, the Gaggia Tell I'm using too has now a electroless nickel plated boiler, so only brass inside the group. There is no smell like the Faema or other copper boiler machines I remember. At the same time, the Elektra Semiauto has almost no smell, but the HX is very small and I flush it a lot during a session.

Márcio.

bobmccarthy

Postby bobmccarthy » Apr 19, 2013, 8:10 am

Jim,

I think the Cimbali Jr boiler is in stainless. Wouldn't the HX tube also be in stainless?

bob

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another_jim
Team HB

Postby another_jim » Apr 19, 2013, 8:33 am

It would need to be long and finned if it were, since it doesn't conduct heat nearly as well as copper. I wouldn't want the job of designing a stainless HX inside an espresso machine
Jim Schulman

bobmccarthy

Postby bobmccarthy » Apr 19, 2013, 8:42 am

Interesting. The machine has always had the rep of having too short of a HX. Maybe it's not so much short but the material used.

bob