Yes, whenever I open a new container of Dannon plain yogurt the whey has already separated out, and I have two choices: stir the whey back in, or pour it off. If I stir it back in, the yogurt will be thinner. If I pour off the whey, the yogurt keeps its shape, but what do I do with the whey? Do I discard it, or do I save it in the fridge until it spoils, or until I accumulate enough to do something with it?
With the way I use plain yogurt now it matters little, since I just mix it with fresh fruit and have it as a snack, or use the yogurt as an accompaniment.
What puzzles me most of all, though, are food writers who suggest dairy substitutes of different thicknesses - tho I'll have to get back to you on that.
And what about the difference in tanginess?