I got a moka pot about 1 year ago, I used only 2 times. After the first time I used it I cleaned it with soap and let it air dry. I noticed then some oxidation (rust) inside the pot, I tried to soak it in hot water and vinegar but it didn't work. So, is it safe to use it (although I smell the metal from the pot)? How can I get rid of the rust? And what is the best way to clean a moka pot?
Based on your photo your pot appears to be made from aluminum based on the white corrosion. This will make cleaning it a bit harder overall but no worries! A great product that will take care of this issue for aluminum or stainless (many other materails as well) is Bar Keepers Friend.
Unlike more abrasive cleaning powders such as Comet and Ajax, Bar Keepers Friend uses oxalic acid as its primary active ingredient. A similar abrasive cleaning product, Zud Heavy Duty Cleanser, also contains oxalic acid. Prolonged use and extended skin contact may cause irritation, peeling and contact dermatitis, which is avoided by wearing gloves. The product can also be an eye irritant.
I just used BKF to clean my stainless percolator pot and it did a great job it looks new! I had baked on brown residue and it took it off in less then a minute. Now my pot looks almost new.
For your specific pot I would get a good scrub brush and some BKF and give it a few minutes scrub and it will look new again! I think BKF may be one of the most underrated tools for us coffee junkies. It gets everything so clean, it even has taken those impossible stains out of the bottom of some of my well used coffee cups.
To prevent corrosion issues in the future the best course of action is to clean it and dry it completely after each use and not let coffee or water sit in it for prolonged time.
Moka pots can be Aluminum or stainless steel. Yours looks Aluminum. Stainless steel should remain stainless forever and should clean up with just soap, water and elbow grease.
If it is magnetic, it is steel not aluminum. So check it with a magnet.
If yours is steel and rusting, then you might have a bigger problem, every-time you use it, it might rust, unless you dry it completely after every use.
To clean aluminum, start by using a mild dish soap and water to remove major debris. To remove the oxidation, make a cleaning solution by mixing lemon juice and cream of tartar, or vinegar, with some water. Then scrub it, rinse and repeat til your satisfied.
Additionally aluminum oxide is not black. Aluminum oxidizes with a very thin layer that is hard for us to see at all and gives it a dull appearance. So I might assume that what is on there is burnt stuff.
The bottom of your pot looks like copper and the crusty gunk looks like scaling (minerals left behind by water that has been boiled or evaporated away). Bar Keeper's Friend will clean that stuff right off, or, for a milder solution, you could first try descaling solution of 1:1 white vinegar to water. Simply dump descaling solution in to the point where the scaling reaches, let it soak for about ten minutes, then brush with a soft brush or sponge.