26 minutes ago, JoNorvelleWalker said:
The buttermilk available to me (and I had assumed all the buttermilk in US grocery stores) is not a byproduct of butter production. It is a cultured milk product that used to be called artificial buttermilk. Like yogurt it can be made with whole milk or reduced fat milk.
Right — most of the buttermilk out there is cultured fresh milk. But traditional buttermilk and cultured low-fat buttermilk are similar enough to be interchangeable, as they have similar fat content. Whole buttermilk (while undeniably much tastier to drink!) could theoretically mess up a sensitive recipe.
The vast majority of what I see here is cultured low-fat buttermilk, but we do have one brand from Maine that claims to be "real" buttermilk:
https://www.kateshomemadebutter.com/Kates-Butter_buttermilk.html
I don't know whether it's actually just the leftovers from the butter churn (I suspect it isn't), but the company's only products are butter and buttermilk. I do know that it tastes better than the other brands!