Stuff stuck to edge of bottle

[Thomas]

Yep to all the above. Potassium tartrate is white, but of course the pigment in red wine will discolor it to pink.

Incidentally, in addition to cream of tartar, the stuff was used in the past to make gunpowder.

I have had a number of wines over the years that have cast tartrates--never detected much of a shift in the product quality. But then, I always saved a little of the crystals to chew on with each glass of wine...