Can anyone explain the purpose of it? I've heard it is ground grapes or something? Doesn't it help egg whites stay stiff or fluffy? but what does it do for breads, like the MJ recipe for crackers?
"Only two things that money can't buy, that's true love and homegrown tomatoes." - Guy Clark
"The man who has planted a garden feels he has done something for the good of the world." - Charles Dudley Warner
Cream of tarter is the acid that makes up part of baking powder. It gives the soda what it needs for it's reaction. It also tastes really tart when mixed with water and is good to drink (if you can choke it down) for a bladder infection - similar effect to cranberry juice. You can also use it in a pinch as an acid mordant when dying wool (although I think vinegar is better).
Yes, it does come from grapes - it's residue left after grape juice has fermented into wine. Yes it is an acid - like vinegar is an acid or citric acid from oranges is an acid.