Could be the main ingredient of the gel like substance they were worrying about.
http://www.post-gazette.com/food/2000010699best1f.asp
Balsamic Syrup
Free-lance writer Virginia Phillips wrote "Cooking in the Kitchen." Buried in the recipe for Thyme-Roasted New Potatoes" was its secret weapon, Balsamic Syrup, a mahogany-colored syrup to drizzle over not just those delicious potatoes, but also mustard greens, spinach, chicken or lamb -- any dish that needs a tangy counterpoint.
1 cup balsamic vinegar
2 scant tablespoons sugar
Stir vinegar and sugar in heavy small saucepan and boil slowly until liquid is reduced to 1/2 cup, about 10 minutes. Mix in 1 tablespoon chopped fresh thyme. Store in a small pitcher in the fridge.