Teryaki sauce becomes viscous after boiled I recently cooked chicken in a Teryaki sauce/marinade, and it turned out great. I cooked the chicken on both sides, and then cooked it in a bath of Teryaki for about 3 minutes. The Teryaki bubbled a lot.

I let the Teryaki sit there in the pan, after cooking, for about 24 hours, and it turned into a tar-like, viscous substance. It reminded me of a video of a guy doing the same with coca cola, which had the same type of affect, which brings me to the question: is this a problem, or a harmless effect expected to happen?

Also, is it bad practice to cook it in a bath of Teryaki like this? Would marinading it be a better alternative? How long should I marinade it for?

This is Yoshinoya's Sweet &amp; Sour (Teryaki-like) sauce, from Costco. Very tasty.
Teryaki has sugar in it.  If you bring it to a boil, the sugar will behave like it typically does in candy-making, and become viscous and possibly tar-like.

You often want this sort of behaviour if you're trying to make a barbeque sauce from meat drippings, but it sounds like you let it boil a little too long.