The stein crafting is part of the NovtumberFest located in the north-western part of the crater. It is led by Moritz. Blowing glass into steins grants the player Crafting experience.
No materials are required to take part in this activity. Interacting with the glass blowing furnace causes the player to gain experience seven times before tiring out, if uninterrupted. Each time yields 71.6 Crafting experience at level 99, and takes 3.6 seconds.
There is a confirmation prompt about gaining experience before starting this activity that can be toggled off permanently.