I find that reducing balsamic is much better, taste-wise, than merely "thickening" it. It intensifies the flavor (not the vinegary taste), brings out the sweetness. It's great drizzled over pureed borscht, aong with a dollop of sour cream.
hiya. i am a bit confused as to what you are saying? this method does reduce it, by evaporation, just as heat does. only without the heat. no yuck fumes and smell in your kitchen. plus, it is more gentle on the vinegar than a heat from a stove would be.
when you use some, just top it off with more from the bottle. that too will thicken, with a couple of days time. it is always on hand.
if the balsamic was properly aged..... a great balsamic is already a rather dense item & reduction often makes that type of complimentary food-item too pungent.
if i could afford the two hundred dollar plus "properly aged" stuff, i would not be doing this!
i am more like in the 12-20 dollar a bottle range. this works well for me. i have tried it with the really cheap stuff, the 3-5 dollar ones, and of course you get out of food what you put into food, so that batch, as well as the bottle i started off with, got tossed.