"Törgellen" is a south-Tirolean (Alto Adige in Italian) "festivity" related to the newly pressed wine, or "Vino Novello" in Italian.
Summing up in English: the modern tradition is an excuse to have a big meal with friends and sample some of the vino novello.
Our experience in Innsbruck has been that not everyone is clear on the concept. We went to one last year, and while we had a great time with our friends there, and ate well, I was pretty much the only person to order wine! That’s sort of like having a Thanksgiving dinner, and everyone eating pork chops.