Another thought: With wine (cider, etc) there's no heat in the process. Who knows what happens to the metabisulfites when you boil them for hours in the sap. For all you know, they have some kind of noxious reaction to the sugar sand and create a nasty flavor in your syrup. I wouldn't risk it, but if you want to, do it in a small and self-contained batch.

Cheers,

GO