Do you have an interest in making butter as well? I use the buttermilk that I'm left with after making cultured butter for baking all the time and I'm very happy with it. I use heavy cream, usually a litre or two at a time, with a pinch of meso aroma culture. Cover and leave at room temp for a while before making butter in the blender/mixer/food processor. I have left it as little as 6 hours and as many as 24. 24 hours was my favorite, both for the flavor of the butter and the buttermilk. If it cultures less time, I find that the buttermilk is improved after a day or so.