Pat, thank you for the excellent information. My apologies for spreading confusion and for suggesting your prior post may have contained incorrect information.

I'll measured the residual chloride content of my RO system to see if there's an issue there and report back.

I'll also try to find out if the seller performed a descaling prior to shipping.

I really want to get to the bottom this.

Thank you so much for the help!

Cybis wrote:Argh, that could very well be. I'll switch to rpavlis to be on the safe side.
I'm still surprised, could corrosion happen this quickly?

Brass E-61 mushrooms are infamous for losing their plating. Something has made pinholes in the plating and corroded the brass (green deposits are formed from the copper in brass). It's very common, and I don't know if water is always the cause.

When working with water formulas for espresso machines, it is important - and fairly easy to check - that the water's pH is above 7 (basic). As an example, my tap water is around 9.5. Water with pH ≤ 7 will contribute to corrosion, especially if there is no available calcium in the water to form protective (on bare copper/brass) limescale. (Too much limescale is not good.)

After pH, the targets are to reduce/eliminate corrosive agents - typically chlorides and sulfates.

Then there is taste, which is split into two components - those agents that affect extraction and thus indirectly taste, and those that impact taste alone. For example, the magnesium that you added does not seem to affect extraction (more-or-less RPavlis (RIP) was right, and Hendon was wrong on this point). In other words, you could have added magnesium to the espresso after you pulled the shot and have had the same flavour change/enhancement.

Good point about pinholes, etc. On those small, localized scales, lots of normal chemistry calculations go out the window because chemistries in pits can be widely different.

Plated brass E-61 mushrooms are surprising magnets for both scale and corrosion. The corrosion is especially common on the spots where the plating has flaked off, and it seems that it always flakes off even with careful water. I sometimes wonder if that's some sort of galvanic corrosion between the nickel/chrome plating and the underlying exposed brass. I now have a stainless mushroom that stays pristine, but miss having the ability to easily check my mushroom for indications of scale (whitish blobs) and corrosion (blue-greenish blobs).

Cybis wrote:I'm still surprised, could corrosion happen this quickly?

I thought it seemed rather quickly but will defer to folks that do this professionally and see lots of machines in the repair/return shop.

baldheadracing wrote:I thought that 70/30 water was for brewing (IIRC, cupping originally), and not for espresso. I personally wouldn't use sulphates or a neutral pH water in a typical E-61 espresso machine.

That is correct - was proposed to be a starting point for cupping water, but folks started using it for espresso brewing. It doesn't have nearly as much sulfate as most of the Barista Hustle recipes, and the alkalinity (45 mg/L as CaCO3) and pH are good from a corrosion perspective. It should have a pH after equilibration with air at 25 ℃ of about 8.1, and has a calculated pHeq (Puckorius pH that you might use in an LSI calculation) of 6.96. Full strength rpavlis would be similar (pH = 8.3, pHeq = 7.03)

homeburrero wrote:Plated brass E-61 mushrooms are surprising magnets for both scale and corrosion. The corrosion is especially common on the spots where the plating has flaked off, and it seems that it always flakes off even with careful water. I sometimes wonder if that's some sort of galvanic corrosion between the nickel/chrome plating and the underlying exposed brass. I now have a stainless mushroom that stays pristine, but miss having the ability to easily check my mushroom for indications of scale (whitish blobs) and corrosion (blue-greenish blobs).

That's interesting, so the plated brass mushroom act as a sort of 'canary in a coal mine' for water issue.
If you look closely at the pictures, there are both greenish blobs and white milky streaks; not sure if it means anything.

I thought it seemed rather quickly but will defer to folks that do this professionally and see lots of machines in the repair/return shop.

Yes, I'd be interested to hear from professionals as well.

... It should have a pH after equilibration with air at 25 ℃ of about 8.1, and has a calculated pHeq (Puckorius pH that you might use in an LSI calculation) of 6.96. Full strength rpavlis would be similar (pH = 8.3, pHeq = 7.03)

Hmm, I measured my RO 70/30 water pH to be exactly 7.00 (the RO was 6.49). I'm using this device:

https://www.hannainst.com/halor-wireles ... 10532.html

I'll recalibrate and re-measure, but that's an odd discrepancy, isn't it?

Cybis wrote:Hmm, I measured my RO 70/30 water pH to be exactly 7.00 (the RO was 6.49). I'm using this device:

That is an interesting difference. Give the water a day, maybe two in an open container, then measure again at 25 ℃ and let us know. My numbers were based on the aqion calculator, which I think is very reliable, but you never know.
Aqion result for 70/30 water:




Because pH is so strongly affected by dissolved CO2, especially for soft water, and is hard to measure unless you have a nice calibrated meter, I tend to suggest that folks measure their alkalinity and not worry much about pH. And for doing LSI it's hard to know what the pH is after the water has been heated in a pressurized boiler, so for that I think it may be better to use the Puckorius pHeq rather than a measured pH.

pHeq: (From Jim Schulman's Insanely Long Water FAQ) :
pHeq = 1.465*log(Alkalinity) + 4.54

homeburrero wrote:That is an interesting difference. Give the water a day, maybe two in an open container, then measure again at 25 ℃ and let us know.

Ok, with the caveat that I currently only have pH 4 and pH 7 calibration solution for my pH meter (waiting on some pH 10), that measurements of low conductivity water with this meter are tricky (drifts a bit), that I don't really know what I'm doing, and that the cats and the wife were getting grumpy with the kitchen takeover, at 25 ℃ I get:

• pH 7.7 for my RO 70/30, and

• pH 8.2 for 70/30 made with distilled water.

Chloride test kit is arriving tonight... although my RO system is the basic hardware store kind with no mineral tricks of any kind, so I'm not sure where the chloride would be coming from.

Is there any validity to the idea that low mineral content water recipes like 70/30 or rpavlis are more sensitive to less than perfect 'base' water? That such water recipes could more easily become corrosive if not perfectly executed?

and if so, are there recipes safer with less than perfect RO water? I'd really like to keep using it.

I had no idea this would be such a rabbit hole
Thank you all for the help!

Cybis wrote:Chloride test kit is arriving tonight... although my RO system is the basic hardware store kind with no mineral tricks of any kind, so I'm not sure where the chloride would be coming from.

If you were getting your RO from an ill-maintained kiosk, and if your local water had very high chloride, then it's possible you might have borderline high chloride in that RO water. Or if you're buying RO with "minerals added for taste", it's very possible that the added mineral is calcium chloride. Since you're running your own RO and checking that it's coming out with low ppm on a conductivity TDS meter you should be fine. Even if your tapwater has extremely high chloride you can pretty much assume that your chloride ion is less than half of your TDS ppm reading of the water out of the RO.

Cybis wrote:Is there any validity to the idea that low mineral content water recipes like 70/30 or rpavlis are more sensitive to less than perfect 'base' water? That such water recipes could more easily become corrosive if not perfectly executed?

Low alkalinity recipes would be more susceptible to possible corrosion caused by corrosive ions (especially chloride) in the base water. If your water's alkalinity is above the typically recommended 40 mg/L then I don't think this is a valid concern. 70/30 has an alkalinity of 45 mg/L and full strength rpavlis has an alkalinity of 50 mg/L, so you should be fine there even if you underdose your minerals a little.

P.S.

Cybis wrote:pH 8.2 for 70/30 made with distilled water.

Thanks for reporting back! That means I can keep using aqion to do pH calculations that would otherwise be a pain in the butt. I also use it to do conductivity calculations.

Good to hear that your pH is higher than neutral.

Pressino wrote:What is the chloride concentration in this water? How exactly did you make this 70/30 water? Staring with RO or distilled or just "water softened" tap water (which could have had a high chloride content to begin with)?

Got the Chloride test kit today. There's no detectable chloride in the base RO water.