CHAPTER XXXI
BUTTER
“From milk,” continued Uncle Paul, “we make butter and cheese. I have just explained to you in a few words how the ingredients composing them—that is, cream and casein—are obtained in their separate forms; but further details are now called for, and I will give them to you, beginning with butter.
“The material necessary for making butter is cream, a fatty substance disseminated through the milk in excessively fine and almost invisible particles. When milk is left undisturbed in a cool place and exposed to the air, these particles of fat rise to the surface little by little and collect there in a layer of cream. An example taken from things familiar to you will explain the cause of this spontaneous separation.
“Oil, you know, cannot in any way be made to dissolve in water. If a mixture of the two liquids is well shaken, the oil divides into an infinity of tiny globules uniformly distributed, and the whole takes on a whitish tint that looks something like milk. But this condition is only temporary. If you stop heating or shaking the mixture, the oil, the lighter part, comes to the surface, globule by globule, and [[307]]soon the two liquids are completely separated, the oil on top, the water at the bottom. If a little gum were added to the water to make it sticky, the separation of the oil would be less easily effected and the mixture would retain its milky appearance for a longer time; nevertheless the two liquids would always end by separating.
“The fatty matter composing butter behaves in the same way as the oil of our experiment. It is not dissolved by the milk; it is simply divided into very minute particles that are held in place by a liquid thickened with casein, just as water thickened with gum holds for a long time the tiny drops of oil. Left undisturbed long enough, these oily particles free themselves and rise to the surface.”
“Cream rises to the top of milk,” observed Jules, “just as oil that has been shaken up with water rises to the surface; only the separation is slower on account of the casein that thickens the liquid.”
“That is the secret of this curious separation. Milk is placed in large earthen nappies, smaller at the bottom than at the top, and thus a large surface is exposed to the cooling action of the air, which hastens the separation of the cream. The full nappy is put in a cool and very quiet place. In summer half a day is long enough for the rising of the cream; in winter it takes at least twenty-four hours. When the separation is finished, the cream is removed with a skimmer or a large almost flat spoon.
“Cream is yellowish white, oily to the touch on account of its greasy matter, and sweet and very [[308]]pleasant to the taste, having the flavor of both fresh butter and cheese. It is most delicious eating.”
“We know that,” Emile assented, “from those capital sandwiches Mother Ambroisine makes for us with cream on feast days.”