Corrosion in espresso filter holder I have thoroughly cleaned my espresso coffee machine, and found signs of corrosion under the layer of tar inside the filter holder:



Judging by the weight of the holder and corrosion type, it's aluminum.

What should I do? Leave it? Scrape it off? Get a replacement?

Is  there a way to prevent this in the future? I suppose getting less sour coffee would help, but unfortunately that's not the kind I like.
Although I have not a real answer as for is hard to tell without specifically knowing the metal/metal treatment/alloy, posting to Chemistry SE might help. To me it looks like a plated Aluminum that got oxidized where the protection dropped.  Aluminum oxide is self protecting so you should not worry much, your filter cup has still a very long lifetime.