Butter is the fat of milk, containing small proportions of caseine, water, and salt (the latter mostly added), and possessing a somewhat granular structure. In its preparation the fat-globules of cream are made to coalesce by the process of churning, and are removed from the residual buttermilk. Its colour, due to lactochrome, varies from white to yellow, according to the breed and food of the cow. The fatty constituents of butter are butyric, caproic, caprylic, capric, myristic, palmitic, stearic, and oleic acids, which are combined with glycerine as ethers; the first four are soluble in hot water, the remainder insoluble. It is very probable that butter fat is composed of complex glycerides, i. e. tri-acid (presumably oleic, palmitic, and butyric) ethers, of the following character:—
| C3 H5 |
| O.C4 H7O |
| O.C16H31O | ||
| O.C18H33O |
The table on [p. 64] exhibits a summary of the results obtained by various chemists by the analysis of numerous specimens of genuine butter.
Dr. Elwyn Waller found the following variations in the constituents of pure butter:—Fat, from 83 to 85; water, from 8 to 10; curd, from 1 to 3; salts, from 3 to 5 per cent.
Butter fat fuses at 28° to 37°, and at 37°·7 its specific gravity ranges from 0·91200 to 0·91400. The most common adulterations of butter consist in the addition of water, salt, colouring matters, and various foreign fats (notably oleomargarine). The first two admixtures are easily recognised by the proximate analysis; the detection of the last sophistication involves a somewhat elaborate examination of the fatty constituents of the butter.
| Analyst. | No. of Samples. | Water. | Fats. | Curd. | Salts. | ||||||||||
| Maximum. | Minimum. | Average. | Maximum. | Minimum. | Average. | Maximum. | Minimum. | Average. | Maximum. | Minimum. | Average. | ||||
| per cent. | per cent. | per cent. | per cent. | per cent. | per cent. | per cent. | per cent. | per cent. | per cent. | per cent. | per cent. | per cent. | |||
| König | 123 | 35·12 | 5·50 | 14·49 | 85·25 | 76·37 | 83·27 | 4·77 | 0·25 | 1·29 | 5·65 | 0·08 | 0·95 | ||
| Bell | 117 | 20·75 | 4·15 | 14·2 | .. | .. | .. | 4·02 | .. | 1·2 | 15·08 | 0·5 | .. | ||
| Hassall |
| 48 | 15·43 | 4·18 | .. | 96·93 | 67·72 | .. | .. | .. | .. | 2·91 | 0·3 | .. | |
| 28·6 | 8·48 | .. | 96·93 | 67·72 | .. | .. | .. | .. | 8·24 | 1·53 | .. | ||||
| Angell and Hehner | 30 | 16·0 | 6·4 | .. | 90·2 | 76·4 | .. | 5·1 | 1·1 | .. | 8·5 | 0·4 | .. | ||
| Wanklyn | 50 | 24·9 | 8·6 | .. | .. | .. | .. | .. | .. | .. | 10·7 | 0·1 | .. | ||
| Caldwell | 26 | 30·75 | 10·45 | .. | .. | .. | .. | .. | .. | .. | .. | .. | .. | ||
| Ellis | 12 | 10·5 | 4·9 | .. | 89·7 | 80·8 | .. | 4·9 | 1·1 | .. | 6·2 | 0·1 | .. | ||
| Larue | 12 | 16·5 | 8·0 | .. | 86·9 | 79·14 | .. | 5·5 | 1·5 | .. | 3·60 | 0·4 | .. | ||
| Fleischman |
| fresh | .. | .. | .. | 18·0 | .. | .. | 80·0 | .. | .. | .. | .. | .. | 2·0 |
| salt | .. | .. | .. | 12·0 | .. | .. | 83·5 | .. | .. | .. | .. | .. | 6·5 | ||
| Blyth | 5 | 12·984 | 8·58 | .. | 87·223 | 82·643 | 85·45 | 5·137 | 2·054 | 2·5 | 3·151 | 0·424 | .. | ||
| Schacht | 8 | 9·00 | 1·25 | .. | 98·00 | 87·00 | .. | 0·5 | .. | .. | 6·0 | 0·57 | .. | ||
Proximate Analysis.
About five grammes of the well-averaged sample are weighed out in a tared platinum capsule, and dried for three hours (or until constant weight is obtained) over a water-bath (or over a low flame, constantly stirring with a thermometer), and the decrease in weight (water) ascertained. As a rule, the proportion of water in genuine butter varies from 8 to 16 per cent. The residue in the capsule is then melted at a gentle heat, and the liquid fat cautiously poured off from the remaining caseine and salt, these latter being afterwards more completely exhausted by washing with ether. Upon now drying the residue, the loss in weight will give the amount of fat present. The caseine is next determined by the loss in weight obtained upon incinerating the matters left undissolved by the ether, the remaining inorganic matter being the salt contained.
The proportion of fat present in genuine butter ranges from 82 to 90 per cent.; it should never be below 80 per cent. The average amount of caseine is 2·5 per cent.; greater proportions, frequently occurring in unadulterated butter, render it more liable to become rancid. The ash should consist of sodium chloride, with some calcium phosphate; the amount of salt is quite variable, but it usually ranges from 2 to 7 per cent. The proportion of ingredients, not fat, in butter may be conveniently determined by melting 10 grammes of the sample in a graduated tube, provided with a scale at its lower end, which is narrowed, adding 30 c.c. of petroleum naphtha, and shaking the mixture. After standing a few hours, the non-fatty matters collect in the lower portion of the tube, and their volume is read off. Genuine butter is said to yield from 12 to 14 per cent. (assuming each c.c. to equal one gramme), while adulterated specimens may show 20 per cent. of matters not fat.