How and why buttermilk was added to English medieval butter?

Question

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.

Answer 1

My mother used to churn butter while growing up on the farm in Pennsylvania, during the 1920s and 1930s. The process of making butter leaves whey behind, so it the mixing of the two can happen if the process is not taken to completion.

I found this question interesting, so looked for examples of whey butter. I found this book, printed in 1905, for you to read:

The manufacture of whey butter at Swiss cheese factories, Volumes 130-145

Answer 2

Whey cream and butter have a lower fat content and taste more salty, tangy and "cheesy".

From Wikipedia on whey butter. That may partially address the why.

Whey also has high quality protein, although not really much in its fresh form:

Nutritional value per 100 g (3.5 oz)
Energy 112 kJ (27 kcal)
Carbohydrates 5.14 g, in the form of mainly lactose:
__Sugars 5.14 g,
Fat 0.36 g,
Protein 0.85 g,
Calcium 47 mg
Water 93.12 g

If the water content is reduced or removed the relative amount of high quality protein rises to 13% and the resulting powder has a much longer shelf-life.

Since there were times when whey was simply discarded as waste, adding dried whey to anything is a very cheap protein booster.

Whey butter has got to be good for people who need lots of energy and protein. It is possible that such a combination is even more important when there are dietary restrictions against mixing meat & dairy. I no longer study kosher law, but I seem to recall that rennet is a meat product. If I am correct, then cheese making is more difficult, in which case there may be additional value in "cheesy" whey butter.

Industrial scale butter production involves extracting small amounts of cream from whey, a by-product of cheese-making, and cultures are then added to the cream to improve longevity. Continuous churns are used, with the capacity to produce 22,000 lb of butter per hour. It results in a consistent if perhaps uninspiring product, but there are still companies around making butter the old fashioned way.
_{BBC Food blog: In praise of British butter, 2012}

(I am on a cellphone, so citations are tough)