One pail of good, pure sour cream without any yogurt or flour* will yield about 15 lbs of washed, unsalted** Finnish butter.
Butter must be washed clean in water as warm as river water in the summer, and the water must be changed until it remains completely clear. Then salt the butter with white, dried salt.
One pood of butter usually will take 4½ lbs salt. If the butter is to be stored for a year or longer, add 5 lbs salt.
It is best to pack the butter in an earthenware or glazed vessel. After sprinkling salt on the bottom, pack the butter in layers and compress it as well as possible. Pour highly salted water over the top to the depth of 2 fingers and cover with a clean cloth, tucking in the ends of the cloth so they do not hang down. As the water diminishes, pour on fresh water. The butter may be packed into small tubs of oak, maple, or even alder instead of earthenware vessels, but not into tubs of spruce, pine, or other resinous woods. The tubs must be strong and without cracks, to prevent the salt water from leaking. Old, or used, kegs are preferable to new kegs.