Frankfurt is pretty well known for its apple wine although I never have seen it warmed. Since Wuerzburg is in Franken which has quite a bit of red wine vineyards I would have expected more the standard variety of Gluehwein there. Maybe next time I am over I will see if I can find the mulled apple wine somewhere; sounds tasty. If you want to try the "standard" Gluehwein that recipe is quite good:
4 bottles of red wine
Sugar (amount proportional to quality of red wine, the worse the wine the more sugar you need, add it to taste, but start with about 2 cups; I like to use light brown one)
6 - 8 Cinnamon sticks
Whole cloves
2 Oranges
Whole allspice
2 cups of orange juice
Pour the red wine into a large pot and put it on the stove on a very low heat – DON'T BOIL IT
Cut the oranges into slices and then put about 4 cloves into each slice, then put them in with the wine.
Break the cinnamon sticks in half or thirds and put them in with the wine as well as 10 of the whole all spice.
Add in 2 cups of orange juice.
Add in 2 cups of sugar and stir.
Stir on and off for about 30 mins to give the spices time to infuse with the wine and for the magic to occur, then taste it, and add more sugar as needed (possible up to 4 or 5 cups more in the wine is really bad).
Let it simmer for about 30 mins more (again,
not letting it boil).
Pour it in cups; best enjoyed outside in the cold with friends and family.