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Churning is the process of shaking up cream (or whole milk) to make butter, and various forms of butter churn have been used for the purpose. In Europe from the Middle Ages until the Industrial Revolution, this was generally as simple as a barrel with a plunger in it, which was moved by hand. Afterward, mechanical means of churning were usually substituted and are considered to be far better. Butter is essentially the fat of milk. It is usually made from sweet cream. In the USA, Ireland, the UK and the Nordic countries, salt is usually added to it. Unsalted (sweet) butters are most commonly used in the rest of Europe. However, it can also be made from acidulated or bacteriologically soured cream. Well into the 19th century butter was still made from cream that had been allowed to stand and sour naturally. The cream was then skimmed from the top of the milk and poured into a wooden tub. Buttermaking was done by hand in butter churns. The natural souring process is, however, a very sensitive one and infection by foreign microorganisms 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. == The creation process == 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 has been separated from whole milk and then cooled; fat droplets clump more easily when 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: # Churning physically agitates the cream until it ruptures the fragile membranes surrounding the milk fat. Once broken, the fat droplets can join with each other and form clumps of fat, or butter grains. # As churning continues, larger clusters of fat collect until they begin to form a network with the air bubbles that are generated by the churning; this traps the liquid and produces a foam. As the fat clumps increase in size, there are also fewer to enclose the air cells. So the bubbles pop, run together, and the foam begins to leak. This leakage is called buttermilk. # The cream separates into butter and buttermilk. The buttermilk is drained off, and the remaining butter is kneaded to form a network of fat crystals that becomes the continuous phase, or dispersion medium, of a water-in-fat emulsion. Working the butter also creates its desired smoothness. Eventually, the water droplets become so finely dispersed in the fat that butter’s texture seems dry. Then it is frozen into cubes, then melted, then frozen again into bigger chunks to sell. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Churning (butter)」の詳細全文を読む スポンサード リンク
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