Bog Butter

Bog butter find*

Ful medames, as I mentioned in my post on that beany breakfast dish a few weeks ago, may originally have been prepared by burying a container of fava beans in the ground.  Yesterday I learned from the Nordic Food Lab that there's a more common food that was prepared, or at least stored, through burial: butter. 

Archaeological finds in Scandinavia and Ireland include caches of long-buried butter, changed by centuries underground into a waxy substance that can be confused with tallow.  However, because bogs create an anerobic environment and highly acidic environment, bacteria do not proliferate, and butter buried in an appropriate container does not spoil once buried.

Most bog butter finds feature some kind of container. Often that container is a wooden barrel or churn, as is depicted in the image to the left. Baskets apparently also were used. In addition, sometimes the butter was also wrapped in plant material, such as sedge leaves or moss. 

The folks at Nordic Food Lab believe that such burials were motivated, not just by the desire to preserve butter in a milieu where refrigeration technology did not exist, but by a desire to impart different flavor qualities to butter, making it more interesting. So they decided to make their own "bog butter" to demonstrate the plausibility of this theory, and they wrote about the process of butter making and burying at length here.

The Nordic Food Lab folks chose to wrap their freshly churned butter with hypnum moss and place the wrapped butter in birchbark containers before burying it about a meter (39 inches) deep.  They did not add salt to the butter before burying it, because no salt is found in the bog butter finds.  Consequently, the Nordic Food Lab people suggest that burial was used for butter preservation when salt was unavailable.  Several different batches were made and buried, in order to permit digging up the butter at different times to see whether the flavor changed as the butter aged.  The first batch was dug up and tasted after three months.  This is what Nordic Food Lab reports about that experience:

In its time underground the butter did not go rancid, as one would expect butter of the same quality to do in a fridge over the same time. The organoleptic qualities of this product were too [sic] many surprising, causing disgust in some and enjoyment in others. The fat absorbs a considerable amount of flavor from its surroundings, gaining flavor notes which were described primarily as ‘animal’ or ‘gamey’, ‘moss’, ‘funky’, ‘pungent’, and ‘salami’. These characteristics are certainly far-flung from the creamy acidity of a freshly made cultured butter, but have been found useful in the kitchen especially with strong and pungent dishes, in a similar manner to aged ghee.

A second batch was dug up after a year-and-a-half, but the post does not go into details about its flavor, saying only, "It is still mossy, green, and earthy – maybe it was the fact that we were also wet, a little smelly, and surrounded by the moss like the thing itself, but the butter, eaten with muddy hands in the clearing in the bog, tasted really good."

What interests me about this experiment is its implications for Viking era cuisine.  We tend to think of butter as the creamy, slightly salty product we purchase from the local market.  The existence of a period-available technique that does not involve salt and gives a strong flavor to butter has implications for Viking food.  If nothing else, it indicates that Viking food may have been more strongly and interestingly flavored than many people have imagined. 



*  Line drawing of a partly destroyed wooden barrel containing bog butter, found in Ireland. From A Descriptive Catalogue of the Antiquities in the Museum of the Royal Irish Academy (1857). Image from Wikimedia Commons.