It may still be stainless steel but even this will corrode especially if it is heated and left wet or exposed to acids. stainless steel works by having "scarificial" elements such as chromium or nickel in it, if these are all oxidesed at the surface corrosion of the iron (the major compomnent of stainless) can occour causing rusting. I suggest rubbing it down with iron wool. Try to allow it to cool in a dry environment and store it in a dry place through the winter (if you have winters like we do in the UK). It is unlikely the rack would be plated as this would be likely to be damaged during heating to you should be OK to use the wire wool. All the best. Hamish