Redwood Foods versions of these are sold in Holland and Barrett, Asda and wholefoods shops. Gravy granules. Just because you're feeding a vegetarian or vegan doesn't mean they have to have 'vegetarian' gravy (you know, the thin watery stuff that looks like a dissolved vegetable stock cube).
If your tongue is stained black or dark brown it may be caused by medications and certain foods/drinks. Drinking several cups of coffee or tea per day may stain the tongue; some people who supplement with green drinks containing chlorophyll may notice a very green tongue.
I have something like this too. A taste of bile and my tongue is yellow-brownish because of the reflux. I've been told that it is a bile reflux - it can promote both gastritis and GERD and it can make significant damage to the mucus unfortunatelly.