The fat may also be determined by drying the butter on asbestos or sand, and subsequently extracting the fat by anhydrous alcohol free ether. The extract, after evaporation of the ether, is dried to constant weight at the temperature of boiling water and weighed.
Casein or Curd and Ash.—The crucible containing the residue from the fat determination is covered and heated, gently at first, gradually raising the temperature to just below redness. The cover may then be removed and the heat continued till the contents of the crucible are white. The loss in weight of the crucible and contents represents casein or curd, and the residue is mineral matter or ash.
Salt.—It is the usual custom in the manufacture of butter in this country to add, as a condiment, a certain proportion of salt. In Europe, the butter offered for consumption is usually unsalted. A convenient method of determining the quantity of salt is found in the removal thereof, from the sample, by repeated washing with hot water and in determining the salt in the wash water by precipitation with silver nitrate. The operation is conducted as follows: From five to ten grams of the sample are placed in a separatory funnel, hot water added, the stopper inserted and the contents of the funnel well shaken. After standing until the fat has all collected on top of the water, the stopcock is opened and the water is allowed to run into an erlenmeyer, being careful to let none of the fat globules pass. Hot water is again added to the beaker, and the extraction is repeated several times, using each time from ten to twenty cubic centimeters of water. The resulting washings contain all but a mere trace of the sodium chlorid originally present in the butter. The sodium chlorid is determined in the filtrate by a set solution of silver nitrate, using a few drops of a solution of potassium chromate as an indicator.
It is evident that the quantity of salt may also be determined from the ash or mineral matter obtained, as above noted, by the same process. If desirable, which is rarely the case, the gravimetric method of estimating the silver chlorid may be used.
499. Volatile or Soluble Acids.—The distinguishing feature of butter, from a chemical point of view, is found in its content of volatile or soluble fat acids. Among the volatile acids are reckoned those which are carried over in a current of steam at a temperature only slightly higher than that of boiling water. As soluble acids are regarded those which pass without great difficulty into solution in hot water. These two classes are composed essentially of the same acids. Of these butyric is the most important, followed by caproic, caprylic and capric acids. Small quantities or rather traces of acetic, lauric, myristic and arachidic acids are also sometimes found in butter. Palmitic, stearic and oleic acids also occur in large quantities. The above named acids, in combination with glycerol, form the butter fat.
500. Relative Proportion of Ingredients.—The composition of butter fat is given differently by different authorities.[502] A typical dry butter fat may be regarded as having the following composition:
| Per cent. | |
| Butyrin | 7.00 |
| Caproin, Caprylin and Caprin | 2.30 |
| Olein | 37.70 |
| Palmitin, stearin, etc. | 53.00 |
Pure butter fat consists principally of the above glycerids, some coloring principles, varying in quantity and composition with the food of the animal, and a trace of lecithin, cholesterol, phytosterol and a lipochrome.
501. Estimation of Volatile or Soluble Acids.—The volatile or soluble acids in butter fat are estimated by the methods already described ([349], [351]). In practice preference is given to the method of determining volatile acids, based on the principle that under standard conditions practically all the acids of this nature are secured in a certain volume of the distillate. This assumption is not strictly true, but the method offers a convenient and reliable manner of obtaining results which, if not absolute, are at least comparative.
The quantity of acid distilled is determined by titration with tenth normal alkali and for convenience the data are expressed in terms of the volume of the alkali consumed. Five grams of normal butter fat will give a distillate, under the conditions given, requiring about twenty-eight cubic centimeters of tenth normal alkali for complete saturation. This is known as the reichert-meissl number. Occasionally this number may rise to thirty-two or may sink to twenty-five. Cases have been reported where it fell below the latter number, but such samples cannot be regarded as normal butter.