Whey Butter is butter made from whey separated from curd during the making of cheese.
It is a strong tasting with a bit of a cheesy flavour to it. It can be salty tasting, if salt was added to the cheese-making process before the whey was drained off. It will be less shiny than regular butter, but oilier, and a deeper yellow. It may have added salt and annatto colouring, just as regular butter would. It may contain residual starter cultures from the cheese batch, and added casein.
There are about 50 pounds (22 1/2 kg) of milk sugar still in every 1,000 pounds (453 kg) of whey. This makes whey of food value in feeding livestock. Before it is fed to livestock though, whey butter can be made from the remaining cream still in it. From 1,000 pounds of whey, with a butterfat content between 3 1/2 and 8 3/4 %, you can produce 3 to 4 pounds (1 1/3 to 1 3/4 kg) of whey butter.
The butterfat content will end up being between 80 and 90%. In Canada, the legal definition is that it must be a minimum of 80% butterfat by weight. In Ireland, it will be 82% butterfat, 16% water, and 2% milk solids.
It is popular in Sweden, where it is sold in most stores as an everyday butter called "mess-smor." It is served as part of an Easter smorgasbord, and a gravy is made from it called "messmörssky."
In other parts of the world, Whey Butter is used commercially in baked goods and in making candies.
Can be substituted for normal butter in baking and frying. In baking, owing to its somewhat oilier texture, it will produce breads with softer crusts and baked goods with a slightly finer texture.
"A mistaken impression prevails in regard to whey butter, some thinking that it is not as good as other butter. Now nothing could be further from the truth. Whey butter made under equally favorable conditions as other butter is its equal except that its texture will not stand the heat as well." -- John Snetsinger, Proprietor, Sweet Briar Cheese Factory in Stiles, Harlow M. Official History of the Cornwall Cheese and Butter Board. Cornwall, Ontario: Cornwall Cheese and Butter Board. 1919, p259.