I'll put on the popcorn.
I suspect there is no one correct answer, and probably varies with application, but is there a preferred boiler material? I assumed stainless steel as it wouldn't add taste - and remember being told to only drink from the cold water tap as the heat would leach impurities out of the joins, solder. etc - but really have no idea. A thread on the Profitec 500 brought up that they chose copper for the boiler which makes sense for the heat exchanger component in particular due the greater thermal conductivity of copper to SS. But for for single or double boiler where owners or manufacturers insulate boilers is thermal conductivity relevant? In fact wouldn't lower thermal conductivity be better? Or better still a double vacuum wall with a thin inner wall to warm quickly (not going there, as I am aware this isn't available, just thinking out loud). So is there a preferred material?
Just daydreaming about upgradeitis and realising like so much on this coffee journey - there is so much I don't know, I don't even know what to dream for!
I'll put on the popcorn.
I have a 1L stainless steel tumbler that I drink from daily....I swear(& verified) I can consistently taste the stainless steel flavor. It's faint but noticeable to me, most people wouldn't care though. So from my perspective, the claim that stainless boiler is tasteless is questionable.
The only odor-neutral material I've had for drinking water is glass, but I've broken too many of them before using the stainless steel reluctantly. I doubt we will have a pressurized glass boiler anytime soon...
Thermal conductivity is only relevant if heat exchanger is involved. Can be mitigated with a good engineering/design. Increase the surface area by longer HX path or smaller diameter tube etc.
On durability front, stainless seems to fail more easily when the owner is not careful about water, particularly with the presence of chloride. Copper boiler will fail too if fed the wrong water...
If taste is a concern (for super taster), a heat exchanger machine would suit better by flushing it out before every session. At least the water is not sitting in the boiler. If you're running a tank machine, I do think the white plastic water reservoir (why oh why) sitting in a heated espresso machine imparts more odor to the water....especially one without boiler insulation..
Acidic (<pH7) or too-soft (distilled or RO) water tends to leach more metal ions so using the right water is more important than boiler material.
I hope you guys are enjoying the popcorn
Thanks Samuel for some good info on water quality, had read about chloride but hadn't realised too soft water would leach minerals out of the bolier - I am worried the RO water I am putting into my brass boiler will try and get the last vestiges of lead out of it!
I also thought the same as you about the plastic tanks, first thing I did was google to see if there were any aftermarket glass or ss tanks, couldn't find any.
Perhaps if it's a lower grade of ss it could make a difference to taste? I'm no metallurgist, but perhaps one's more/less stable than another (18/10, 18/0, etc)?
Perhaps the 2L in the boiler creates enough thermal mass for it to not be an issue. I'd be surprised if zie Germans had overlooked something engineering related. I think so long as the whole machine has been well designed and laid out, there shouldn't be too much of an issue re performance. Copper is softer and could expand more, hence fail at the seams before ss does?? Don't quote me there either.
But who knows re taste, I brew beer and in the early days I could taste the rubber garden hose used to fill the boiler with, needless to say I don't do that anymore. But that was a lot of surface area to taint the water.
Just thinking out loud though, if one can taste the ss, perhaps one should brew a stronger coffee??
As for the plastic, the water container in My Silvia is Polypropylene and deemed to be one of the safer plastics to use. I can't find any stats on leeching and temperatures, but would think it'd have to heat up quite a bit for it to be a taste/health issue. Again, surface area might be a consideration here. But we use a lot of food grade plastics for home brewing (fermenters, hoses) and it doesn't seem to detrimentally affect taste. I'd say 99% of the hoses in pubs serve beer through long polypro runs, are cleaned (hopefully) with solvents etc, and even over long runs don't impart an obvious influence over flavour. Silicone is used on the hot side of brewing and it's stable at boiling point.
I'd say if the plastics are food grade and aren't getting too hot (help needed here but guessing upwards of 70˚C) they're fine to hold water. They might just break down over a period of time.
My experience with Stainless Steel, both cooking and drinking utensils, has been that as long as the oxidation layer on it is left intact no taste is imparted. If that oxidization layer is scrubbed off then there is a very clear taste imparted to the food/drink.
Java "Hates that taste!" phile
Toys! I must have new toys!!!
I thought I was tasting oak in my wine or is it the SS now.😯
To throw a few curly ones into the mix
1) Brass (and copper to a lesser extent) boilers are infamous for the "fish oil taste" - all of them, unless scrupulously flushed, cleaned and maintained. Most cafes get a fail for this one. This disregards the toxicity issue altogether, which is actually why the EU banned them a while back.
2) Cheaper grades of stainless are infamous for the metallic taste so hated by some posters. Most manufacturers seem to be allergic to the extra cost of decent stainless grades. see 8.
3) Plastic - 90+% of them impart an outright evil taste to the water (and milk - which is why I buy my milk in glass bottles).
4) Glass - some glass variants also have a taste taint, although most don't.
5) Most ceramics also have a faint taint. That plus temperature stability is why I switched to dual walled Borosilicate a while back.
6) Aluminium has its own taste - and so do at least most of its exotic alloy variants.
7) Rubber / neoprene has its own "flavour additive". Close to bottom of my list (worse than most plastics).
8) The closer to pure H20, the better it is as a solvent, so all materials tend to leach by the time the water is of a really good quality for making coffee. Of course, this will help to bring out any taint. IMO Jim Schulman's "insanely long water FAQ" is probably skewed by this little gem when he states that some mineral content is desirable.
Perhaps someone can make all items in the coffee path out of a genuinely "non toxic. non leaching. inert material" - if one exists?
Personally, a client of mine tested hundreds of plastic and metal variants to attempt to find a tasteless coffee pod. After 18+ months of testing only one (quite expensive...of course) EU certified plastic passed the taste taste in the sense of being unobtrusive for most roasts. Put in a delicate light roast and make it as an espresso and it still imparted a little taint. When it was made into a latte it was impossible for any of the victims (aka tasters) to pick it.
FWIW, I reckon either go for a top grade stainless (and get prepared for sticker shock) or find some better material - carbon fibre?, teflon / silverstone?, anything...?
PS: No prizes for guessing who has some custom glass water tanks for their espresso machines. Old Norwegian proverb "every little bit helps said the mouse pissing into the ocean".
Wonder if stainless steel and saliva react?
Regardless, like others, my preferred choice of drinking vessel is alcohol = glass, beverages = ceramic.
Never have liked drinking from plastic, metal or paper.
Copper looks great when it's polished up so I vote copper. Currently building a steampunk machine and the attributes of bright copper and brass are very important.
Javaphile thanks for that explanation, I also drink water regularly out of SS and notice when I clean it could taste something - I thought it was my salive which had left the coating. Will be careful not to remove the oxidisation.
Tampit thanks for a very comprehensive answer which leads me to think SS in a good grade might be the choice. Your answer mentioning custom glass water tanks instantly made me thing of getting a fish tank guy to build a custom tank - then I remembered the silicone to hold it together. Great idea.
Noidle for a steampunk I agree copper and brass look great. Incralac for non heat intensive areas will keep it looking that way. Had a brass cistern in my first rental when a teenager, polished and used Incralac Lacquer and looked just as good 6 years later.
I thnk with all these replies mentioning all the different substances which we drink from I am going to become paranoid I had never realised how many different substances