I was wondering, what is special about the sour cream. what does it add to the mix?

I think sour cream, buttermilk and sometimes yogurt makes cakes more flavorful, especially in scratch cakes. I haven't tried them in box mix but this thread talks about it more. HTH

http://cakecentral.com/t/748368/sour-cream-or-buttermilk/15

AI think in all those three things: sour cream, buttermilk, yogurt, the acid in them helps to make a more tender and moist cake as well as adding a tangy flavor component.

AI use buttermilk in place of milk in all my recipes. I like the flavor of it and the fat in it makes for a moister cake

AActually.... Buttermilk has very little fat in it. It's the milk left over after the fat - the butter - has been removed. If you make your own butter from whole, un homogenized milk, you can see this process in action. You skim the cream from the milk, then make the butter curds. You take out the butter curds and what you have left is a very thin milk. But even though it's similar in fat content to skim milk, it reacts chemically different than skim milk, leading to all the yummy tanginess that buttermilk provides. :)

AAlways learning something :) is tha the same for whole cultured buttermilk and fat free

AI've only ever seen one kind at the store "cultured buttermilk" so that's all I know about. I wonder if labeling some "fat free" is just a marketing gimmick though! Lol!

AThey sell both here, but I had a real hard time finding the whole cultured when I went to ohio. All they sold was the fat free kind or low fat