Re: glycerine inedible?

Question

B'Kavod LaRav: Thank you very much for posting sources for this and other responses - they are tremendously helpful! However, the issue with edibility of glycerine gets me to an issue that arose in learning the laws of the fast. The Rabbi in my shul was discussing Sh"'A, RaM"A, and M"B on washing one's mouth out with water. We moved the topic into toothpaste and mouthwash, to which we learned that these are on-par with water (i.e., not permissible unless there is "reasonable discomfort")! The inference was collaborated with an explicit prohibition of the M"B to wash one's mouth with vinegar on a fast day. Well, this actully raises some interesting issues. Using your criterion of "It is inedible:Ask for a cup of glycerine (vinegar), and I welcome you to swallow it & see for yourself", it would seem that vinegar shoud not require a hechsher, since it is equally inedible (if not more so because it is Pogei'ah). Is this your p'saq on vinegar? In othe words, *does vinegar require a hechsher?* If vinegar does not require a hecsher because it is inedible, then please reconcile your response to a prior post (#8516, Re: Vegetarian Restaurants, "Wine & wine vinegar can pose a problem"). Why would wine vinegar be problematic? Does Yayin Nesech apply to inedible substances? If vinegar does requier a hechser, please explain how it would differ from glycerine, which would seem more edible (at least by taste, although glycerine may be equally Pogei'ah). I ask these questions sincerely and respectfully, as I try to understand the boundaries of edibility and kashruth. Thank you, Jack D.