How bad is copper oxide in an espresso machine (on brass part behind shower screen)

[echappist]

This is a new one. I didn't need to descale (and maintain) my machine as often, since we swapped to getting water delivery (and using a filter on top of that).

So instead of doing maintenance every six months, I've waited about a year, and to my surprise, the part immediately behind the shower head has developed a nice patina, presumably due to oxidation of the part. Previously there was only build-up of gunk that I needed to remove, but this was a new one.

So how bad is this? Do I need a new part? FWIW, I was able to scrub off the oxide (and gunk) with steel wool, but I'm not sure if I got ride of everything.

ETA: the part is called the diffusor

[Mark Kelly]

Not a problem, the hot water that flows through that part of the machine won't dissolve copper oxide. If you want to prevent it occuring, backflush occasionally with citric acid.

[9tubes]

@echappist, you didn't write what type of machine you have but it is very unlikely that the diffuser behind the portafilter screen is made of copper. That part is typically made of brass. The patina forms on the brass as it oxidizes but it reaches a natural limit and then stops (unlike steel rusting). I don't think brass dissolves into hot water. If brass did dissolve, the brass diffuser would be shiny. Note I haven't seen any studies on this in espresso machines. Also, there is no need to remove this patina. If the brown you see is from coffee oil buildup it can be removed with a sponge and Calfiza (simple citric acid).

[echappist]

Thanks for your response. You are right, it's brass, not copper metal; I should have been more clear.. The machine is a Rancilio Silvia, V3.

Previously the build up appeared brown (back when I cleaned twice a year), but now this looked like patina on copper-containing alloys, alas my question. Or perhaps it's a copper oxycarbide of some sort.

[9tubes]

With enough time, brass turns the same shade of brown as old copper. Or do you mean it was green?

[Bobonli]

About as bad as your Aeropress in a microwave.

I couldn't resist.

[echappist]

With enough time, brass turns the same shade of brown as old copper. Or do you mean it was green?

It was actually green / teal. Couldn't recall the exact colors, but it was sufficiently different from the normal stuff caked on there to make me pay attention.

I scrubbed it with some steel wool, and now I'm going to be back flushing more often and dissembling the thing more often (every three months).