Contrary to popular beliefs, it very very hard to rust coffee burrs within a normal usage setting even with aggressive rdt (spraying water on beans) or frozen beans grinding.. I have single dose and freeze all my beans, before grinding I will do a quick spray of water to lessen the static further. Till date from my experience with the niche , mazzer jolly single dosing to ek43 I have not encountered any burr rust .
The only time it rusted was when i took out the mazzer burrs and used sponge and dishwashing soap to clean it and air-dry it. It started forming some discolouration after half a day being left out..my guess is the dish washing soap stripped out the oils protecting the metal.