It is not recommended to keep the 奶樽 inside the steamer after the 消毒 process. Once the 消毒 process is finished, it is better to put the 奶樽 inside fridge and use within 24 hours.
After you pick out all the 奶樽 from the steamer, the manual suggests us to let it cool and use dry towel to clean the inner, i.e. keep it dry if not use.
The smell may be come from the dirt accumulated on the silver plate, you could go to Wing On or Mothercare or Ho Fa, they have some powder for cleaning the steamer dirt, you can use it to clean the steamer regularly, e.g. once a week.