Buttermaking was done by hand in butter churns. The natural souring process is, however, a very sensitive one and infection by foreign micro-organisms often spoiled the result. Today's commercial buttermaking is a product of the knowledge and experience gained over the years in such matters as hygiene, bacterial acidifying and heat treatment, as well as the rapid technical development that has led to the advanced machinery now used. The commercial cream separator was introduced at the end of the 19th century, the continuous churn had been commercialized by the middle of the 20th century.
Changing whole milk to butter is a process of transforming a fat-in-water emulsion (milk) to a water-in-fat emulsion (butter). Whole milk is a dilute emulsion of tiny fat globules surrounded by lipoprotein membranes that keep the fat globules separate from one another.
Butter is made from cream that's been separated from whole milk and then cooled; fat droplets clump more easily when they’re hard rather than soft. However, making good butter also depends upon other factors, such as the fat content of the cream and its acidity.
The process can be summarized in 3 steps:
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Butter churns have varied over time as technology and materials have changed.
With electric mixers and food processors commonly available in most house holds kitchens. They are used to mix the cream until it is close to forming solid butter. Then mixed by hand to remove the butter milk and water.
The Household Cyclopedia of 1881 instructs:
"Let the cream be at the temperature of 55° to 60°, by a Fahrenheit thermometer; this is very important. If the weather be cold put boiling water into the churn for half an hour before you want to use it; when that is poured off strain in the cream through a butter cloth. When the butter is coming, which is easily ascertained by the sound, take off the lid, and with a small, flat board scrape down the sides of the churn, and do the same to the lid: this prevents waste. When the butter is come the butter-milk is to be poured off and spring water put into the churn, and turned for two or three minutes; this is to be then poured away and fresh added, and again the handle turned for a minute or two. Should there be the least milkiness when this is poured from the churn, more must be put in.
"The butter is then to be placed on a board or marble slab and salted to taste; then with a cream cloth, wrung out in spring water, press all the moisture from it. When dry and firm make it up into rolls with flat boards. The whole process should be completed in three-quarters of an hour. In hot weather pains must be taken to keep the cream from reaching too high a heat. If the dairy be not cool enough, keep the cream-pot in the coldest water you can get; make the butter early in the morning, and place cold water in the churn for a while before it is used."