Descaling Effects on Brass And Copper

This primarily refers to Citric acid, but will happen with any acidic solution without inhibitors

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Brass is an alloy of metals primarily copper and zinc for the common brasses (roughly 70% copper 30% zinc. Using Citric acid on Brass dissolves a minute amount of the metal (don't worry it won't hurt it), but the dissolved copper can re deposit (the zinc doesn't) back onto the surface of the brass, giving a "salmon pink" colouration. This is such a thin layer that it can easily be cleaned off. With pure copper pipes this same effect redeposits fresh copper back onto the pipe, with a characteristic "salmon pink" tinge, that is quite distinctive compared to the "aged" copper patina.

How will you know a component is brass? because they go copper coloured and after cleaning (the tarnish) it will become brass coloured again…a pretty good clue. Most prosumer machines portafilters are cast from brass and then nickel or chrome plated.

In historical preservation of metals, they often clean up things they have found with weak citric acid, but to prevent this problem with brass or copper they use Thiourea (which is almost certainly Toxic to humans!) as an inhibitor to prevent/reduce chemical attack on the brass itself….but of course you don't need to worry, because the amount of damage is so small, it's not worth worrying about in everyday use…they just don't want to have to clean artifacts any more than they have to and the artifacts are not in contact with food..

So to summarise:

Any time you descale, yes your disolving a minute amount of the copper and brass in your machine (the bluish colour you see in the water is from dissolved copper compounds…put an iron nail in it and see what happens!). The amount is very small, and unless the acid is very strong or you are descaling agressively and very frequently, you won't do any damage to your machine. you will certainly do more damage by not descaling. Some commercial descalers do have inhibitors and buffer salts to minimise this effect, but usually they are much stronger than citric acid to start with.

Oh, if the inside of your portafilter goes brass coloured after a long period of use, don't worry, it wont hurt you and you won't taste anything in the coffee, brass and copper have been used in water supply plumbing fittings, kettles and cooking pots for a very long time and as far as I know, don't do you any harm.