My question engages in the history of butter. I'm not sure if this is the right place to ask but I will give it a try.
I read an old Jewish text (Sharei Dura 78) dated to the 13th century that mentions English butter which was mixed with whey or buttermilk (text is unclear) while discussing its permissibility for consumption. It also relates that the buttermilk could potentially evaporate from the butter after four days, which in turn would make the butter dry.
This made me wonder how the buttermilk was added to the butter, did they actually mix the buttermilk in the butter (meaning that the buttermilk curdled along with the butter and became part of it), or was it something separate in which the butter sat in (similar to cheese in brine), which would somewhat explain the evaporation of the buttermilk? Is there any evidence as to how this process was done in the olden days?
I would also like to know whether the practice of adding buttermilk to butter is still practiced nowadays (commercially or non-commercially)?
If anyone can shed light on any of these points I would be grateful.