In the old days, Icelandic butter was made in a plunger churn. Butter was produced using milk both from cows and from ewes. The milk was placed in a trog (a wooden tray with high sloping sides) and left to stand, after which the skimmed milk was drained from beneath the cream through a hole in one corner of the trog into a separate container. The cream was then churned in the plunger churner. This was quite hard work, and it was considered quickly accomplished if it took only 6–7000 plunges to make the butter. As a matter of fact, there are stories of housekeepers saving themselves some work by tying the churner onto the back of a herder before he left to herd the sheep so that the butter was churned while he was running after the animals—this, however, would not have been a common method. Once the churning was finished, the butter was kneaded to eliminate most of the buttermilk, then formed into blocks. Skimmed milk and butter milk (the liquids that remain after butter has been churned) were not wasted—buttermilk was considered a delicacy and it was sometimes mixed with skimmed milk.

In Iceland, butter had generally turned rancid by the time it was used, and in fact it was not considered to be tasty enough unless it had “gone off”. Sometimes the butter was mixed with lamb fat, and it wasn’t until the 19th century that salt was added. It was stored in pods or caskets called “grásída” (greysides), often for very long periods. People usually had considerable stores of butter; it was used extensively, and it was considered a source of strength during the harsh winter months when people needed to consume a lot of fat. The recommended portion was approximately 1700 g a week per person. In some places, children were slathered with butter to improve their health, and butter was given to weak lambs. There are stories of butter being used instead of soap and, according to folklore, butter mixed with fish liver oil and the brain of a raven could be used as a cure for swellings.