How do you make cream of tartar?

I know it's a byproduct of winemaking, but how do you actually harvest the cream of tartar after you've made the wine? I can't find any instructions on how to do so. Please don't say, ';buy it at the store';; that's not what I'm asking. I'm not asking where to get it, I'm asking specifically how one would go about producing cream of tartar as a byproduct of making their own wine.How do you make cream of tartar?
If I recall it is the residual foam left over after having allowed the wine to ferment in an oak barrel.How do you make cream of tartar?
I have no idea. I always buy it.
go to cooks.com they have a recipe for everything