Examination of the Butter-fat.
The most common and important sophistication of butter consists in the addition of foreign fats, embracing both animal fats (oleomargarine and lard) and vegetable oils (cotton-seed, olive, rape-seed, cocoa-nut, almond, palm, etc.). Of these, oleomargarine is doubtless the most often employed. Oleomargarine is the more fusible portion of beef fat, and is prepared by straining the melted fat, allowing the oil thus obtained to stand for some time at a temperature of about 24°, when most of the stearine and palmitine will separate out, and cooling the remaining oil until it solidifies. This is next churned with milk, a little colouring matter (annato) being added, and the product is then chilled by mixing it with ice; salt is now added, and the mass is finally worked up into lumps.
It is stated that fifteen establishments in the United States are engaged in the manufacture of oleomargarine, the annual production in the State of New York alone being about 20,000,000 pounds. The rapid increase in the manufacture of oleomargarine is shown by the following statistics:—In 1880 this country exported 39,236,655 pounds of butter and 20,000,000 pounds of oleomargarine, while in 1885 the exportation of butter declined to 21,638,128 pounds, and the exportation of oleomargarine reached nearly 38,000,000 pounds. The present production is said to approximate 50,000,000 pounds per annum. The most characteristic difference in the composition of genuine butter and oleomargarine consists in the greater proportion of soluble fats contained in the former. This is illustrated by the following comparative analysis of the two products (Mége Mouriès):—
| Genuine Butter. | Oleomargarine. | |
| per cent. | per cent. | |
| Water | 11·968 | 11·203 |
| Solids | 88·032 | 88·797 |
| 100·000 | 100·000 | |
| Solids: | ||
| Insoluble fats | 75·256 | 81·191 |
| Soluble fats | 7·432 | 1·823 |
| Caseine | 0·182 | 0·621 |
| Salt | 5·162 | 5·162 |
| 88·032 | 88·797 |
Lard is likewise occasionally used in the United States as an admixture to butter, the product, “lardine,” being sold either as oleomargarine-butter, or as the genuine article. Dr. Munsell mentions a factory in New York city where the weekly output of larded butter is 5000 pounds. As a result of the efforts of the New York State Dairy Commission, it has been estimated that the sale of imitation butter in this State in 1885 suffered a decrease of about 60 per cent., although the quantity manufactured in the United States showed an increase of 50 per cent.
The specific gravity and melting point of butter have been suggested as criteria for its purity; in most cases, however, these determinations possess a rather limited value; as already stated, butter fat, at the temperature of 37°·7, has a density ranging from 0·91200 to 0·91400.
The relation between the specific gravity of a fat and the proportion of insoluble acids contained was first noticed by Bell. This is shown in the following table which refers to pure butter fat.
| Specific Gravity at 37°·7. | Per cent. Insoluble Acids |
| 0·91382 | 87·47 |
| 0·91346 | 87·89 |
| 0·91337 | 87·98 |
| 0·91290 | 88·48 |
| 0·91286 | 88·52 |
| 0·91276 | 88·62 |
| 0·91258 | 88·80 |
| 0·91246 | 89·00 |
The following results have been obtained by the analysis of samples of various animal fats, and oleomargarine butter.