© Denzil Green
Butter is a spread made from solidified cream. It can be used at the table as a "condiment", or in the kitchen as an ingredient.
To make butter, the fattier part of milk called "cream" is taken from the milk, and then churned. Eventually globules form, and start to clump together. Two products result at the end: the globules which form a mass, called butter, and the liquid left over, which is called "buttermilk".
Salt is often added to butter. The purpose used to be to act as a preservative, slowing down the growth of bacteria in the butter; today, it is added mostly as a flavouring for those who are used to or prefer the taste of salted Butter.
Sweet Cream Butter is unsalted butter. It is common in Ireland, England, New Zealand and North America. Cultured butter (made from cream to allowed to stand for a day with starter cultures in it) is common in Europe.
North American butter by law must have a minimum 80% butterfat in it; speciality American butters and everyday European butters tend to start at 82% to 83% and can range up to 86% butterfat.
Higher butterfat-content butter can be critical in chocolate and pastry making, because it means less water in the product.
In Canada, most manufacturers only supply the bare minimum legally-required 80% butterfat in their butters.
It takes 5 litres (10 US pints) of milk to make 225 g (1/2 pound) of butter.
As of 2012, the largest-selling butter brand in the United States is Land O'Lakes, with 25% of the market share. 
Butterfat CreamButterfat is the fatty part of milk that is used to make butter. It takes about 100 pounds of milk to produce 3.6 pounds of butterfat, though in some herds that amount is increasing to 5 pounds owing to better selective breeding. To separate butterfat out of milk, pasteurized whole milk is whizzed around in separators rotating 30,000 times per minute, separating off up to 40% of what is called Butterfat Cream.
Butter ChurningThe churning process breaks down a membrane around the butterfat molecules, allowing them to adhere to each other, thus coagulating to form butter. Butter forms in the final two minutes of the churning process. The leftover milk (the "buttermilk") is drained from the churn, then the butter is washed with water to remove any residual milk -- the proteins in the milk would shorten the life-span of the butter.
Butter will smoke at 160 C (320 F.)
1 cup of margarine; or
7/8 cup (7 oz / 200 g) lard (or shortening) and 1/2 tsp. salt
7/8 cup (7 oz / 200 ml) of vegetable oil
Don't substitute oil for butter for in a pastry recipe. It is okay to do so in most recipes for cakes and muffins.
1 pound Butter = 4 sticks
1 stick Butter = 1/4 pound = 1/2 cup = 8 tablespoons = 4 oz = 115 g
1/4 pound Butter = 4 oz = 115 g = 1/2 cup = 8 tablespoons
8 oz Butter = 225 g = 1 cup
4 oz butter = 100g = 1/2 cup
1 (450 g) pound Butter = 2 cups
1 oz Butter = 30 g = 2 tablespoons
1 tablespoon of butter = 1/2 oz = 15 g
A knob of Butter is, at best, an inaccurate measurement that really means a "dollop". While certainly, some people maintain that a "knob" is around 2 tablespoons, there are as many folks that maintain that the closest measurement to a "knob" is about 2 tsps.
Another definition for "knob" of butter is the amount of butter you get when you slice the corner of a block of butter to form an isosceles right-angled tetrahedron equal to half the height of the block of butter. This averages about 2 tsps.
Welsh Butter has traditionally been quite salty. The cow herds there produced great surpluses of milk, which meant surpluses of Butter that needed to be preserved for a longer time. Salting the Butter well was a way of doing this. Even though the milk surplus days are over, the Welsh still retain a taste for salty Butter.
The first commercial creamery in America to make Butter started business in Iowa in 1871.
The American Congress decreed in 1923 that American Butter must have a minimum 80% butterfat in it; that law remains unchanged today.
A firkin of butter was 54 pounds (24 1/2 kg) in weight.
Literature & Lore
"Just imported from Rotterdam, a large quantity of excellent DUTCH BUTTER of a fine straw colour, the produce of the most esteemed Dairies in Holland, and of so exquisite a flavour as cannot fail to gratify the most delicate taste. The butter being put up in small packages (from 12 lb. to 28 lb. and upwards) renders it very convenient for the use of small families. By the same ship, a quantity of DUTCH RUSKS, sold in casks, and by the pound." -- Advertisement placed by "The Italian Warehouse in The Edinburgh Advertiser. Edinburgh, Scotland. Friday, 26 December 1823. Page 1.
"With respect to the prices of butter, it appears by the household-book of Lord North that a pound of butter in the reign of Queen Elizabeth cost fourpence: at the present time (the summer of 1835), a pound of the best butter in the west of England costs from sevenpence to eightpence, while in the metropolis the price is fourteenpence. A large portion of the butter consumed in London is in rolls without any impression. Dutch and Irish butter is also imported in considerable quantities, but the flavour and quality are not considered equal to the butter of this country; and the Dutch butter often abounds with hairs and other impurities." -- The Penny Magazine. Volume 211, 18 July 1835.