I have never used either sour cream or buttermilk in any cakes. I bake mine free of dairy and use rice milk or almond milk that I substitute for reg. milk. So I always avoid recipes with sour cream or buttermilk. But I have noticed that recipes containing those ingredients are popular so I'm thinking it has to be a reason why it is added. Does anyone know the affect any of them have on a cake. Flavor? Texture?
I read that it's easy to make buttermilk by adding lemon juice or vinegar to milk. Could I do that to rice milk or almond milk as well?
Would anyone know if there is a dairy free alternative to use sour cream? There are dairy free yogurts but would that have the same affects?
I'm sorry I ended up with so many questions, thank you for taking your time to read all of this!

both buttermilk and sour cream are additional fat (additional to the butter). they both impart moistness. buttermilk in my opinion makes a more tender cake than sour cream.

thank you. Good to know, I thought it had to do with the acidity but was only guessing so now I know. I think I will give a buttermilk substitute a try (adding a tbsp vinegar to a cup of rice milk) and see if I like it -or if it even works!!!

I'm not sure that will work (although it doesn't hurt to try) the vinegar "curdles" the milk which is why it's a good sub for buttermilk.. I haven't ever had rice milk so I don't know if it can curdle

It does work with soymilk though, I do that when I need to make a lactose free cake

There are vegan sour creams available at health food stores also. I baked a dairy free cake with vegan sour cream and goats milk. I thought it tasted a little funny, but it may have been in my head! The texture did not turn out the same as when I use regular milk and sour cream but it was not terrible; just different.

Ok. So if the trick to "making" buttermilk is to have it curdled, then I can just try different non-dairy milks (rice, almond or soy) and see what happens without even making a cake. Is it the protein that curdles? Is not that how they make tofu? (Adding lemon juice to soy milk?) Ok. that was just thinking out loud. Not trying to change the topic.
Thanks for all the help!