When steaming milk it's possible for some of the milk to be drawn up the steam pipe at the end of the process. If enough of the milk gets into the boiler it will cook on the heating element and result in smelly steam. The only way to get rid of it is repeated heat/flush cycles or replace the heating element. To prevent this, every time you steam milk, when you're done remove the pitcher and open the steam knob again for a few seconds. This will clean the wand out.