The butter is the most sensitive animal fat, irreplaceable in the kitchen for his contribution to flavor that is the same of milk from which it derives.
The source is fat emulsified and suspended in milk. Being lighter than water, collects on the surface of standing milk that is skimmed off for “surfacing” or “spin. ” This ‘cream’, first pasteurized and matured, is then shaken vigorously in the ‘churn’ process that separate the fat molecules from water and other substances, just turning into butter, which, however, still contains a certain amount of water (buttermilk) and should be further worked with vigorous kneading and washing.
In some regions, the cream is boiled before you reach into the churn, in others it is aged for a time that varies depending on the ambient temperature and the acid will work, finding a way to extract the most delicate butter and an easier storage. The air, light and bacteria alter the butter and rancid: it changes color and acquires so unpleasant smell and taste.