The subject of why steins have lids has has generated much controversy among stein collectors over the years. This is a link to a video of a presentation on the subject at the 2006 SCI convention in Valley Forge by Ginger Gehres. This video covers all aspects of the topic, and runs for 45 minutes, so make sure you are comfortable when you start watching it. Click on the link below to start the video.

This video is also available for loan or purchase from the SCI Library/Museum Archives.
It would make an interesting presentation at a local chapter meeting.