A Winnowing Gala is an event often held in reception halls, where all the elves on one's matchmaking list are all invited in order to narrow down the choices for a permanent match. Individuals can choose to not hold one, but it is a common tradition.

Some, like Jolie Lucine Ruewen, have already made up their minds by the time they get their scroll and have no need for a gala, and others, like Sophie, find the idea incredibly odd, and might not participate in the event. 

Sophie shudders after imagining King Dimitar coming to her Winnowing Gala, possibly implying that she might have a Winnowing Gala.  

Only your parents and the people on your match list and their parents are allowed at the gala. Usually, a winnowing gala is held for every match list, all of 100 people, but some don’t show up. It is a tradition that people sign up to dance on ‘dance cards’, because it makes the choice of whom to talk to first easier.  
