This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
The importance of using coloring of the best quality cannot be overestimated. A beautiful brilliant color will make your goods more saleable, but they must not contain any injurious ingredients, and the color must be unaffected by light or 'acids. In order to enable bottlers to determine the value of their fruit coloring, we subjoin the following tests: Aniline or fuchsine is indicated if the color stains the bottles; also, if on the addition of an acid or of sulphite of soda the color fades away and disappears altogether. Cochineal or carmine is precipitated on the addition of acid. Put a few drops of sulphuric acid into a tumbler of water colored with any preparation of cochineal, and let it stand a few hours. These colorings can frequently be detected by a strong smell of ammonia.
To produce a persistent head on the carbonated beverages some substances are added to the compound syrups to bring about that effect, and make the beverage appear frothy. The commercial preparations are called "gum foam," and are chiefly prepared from soap bark, soap root or senega, and allied roots or substitutions; also from gum arabic. For bottled beverages the preparations of gum arabic are not well adapted, since they are of a very unstable character, and liable to fermentation and inversion. For draught beverages they are suitable and for this purpose is also employed the whites of eggs.
Soap bark or Quillaia-bark is the inner bark of Quillaia saponaria, from a tree indigenous to Peru and Chili. The bark comes in flat white pieces. For the purpose of making extracts, etc., the bark is crushed and sold in'this state. Its infusion foams like a solution of soap. Quillaia bark contains numerous crystals of sulphate of calcium, a small quantity of starch and considerable saponin, to which it owes the name soap bark.
Soap Root or Soap wort is a European herb, growing also in North America, of which the root is collected, which contains also saponin, and is free from starch.
Senega, seneka root, senega snake root, is found also in North America. It contains senegrin, which is regarded identical with saponin. Of these three resources soap bark is the cheapest, and therefore extensively employed for preparing "gum foam".
Prepare the extract as follows: Soap bark, crushed, one pound; alcohol, one pint; glycerine, one pint; water, two pints. Mix alcohol, glycerine and water, saturate the bark with six ounces of the mixture, pack tightly in a percolator; close the lower orifice and add enough liquid to leave a stratum above the bark. Macerate twenty-four hours, then proceed to percolate; add sufficient alcohol, glycerine and water in the above proportions, until four pints of extract are obtained. This is an excellent preparation and has no injuri-. ous effect upon the human organism, being soluble in aqueous liquids and having no deleterious influence upon the beverages or their components. A preservative is not required, the alcohol and glycerine preserving it. The proportions are from two drachms to one ounce to a gallon of syrup, according to the "foam" required on the beverage.
This may be prepared by macerating one pound of the crushed bark in five pints of alcohol, and exhausting by percolation.
Soap bark, one pound; gum arabic, one to four ounces; water, one gallon; or only soap bark and water. Pour boiling water on the bark, add the gum arabic, stir until dissolved. When cold filter through a filtering bag. About two ounces per gallon of syrup are required to give a "head" to the beverage. This is a cheaper product and better adapted for dispensers than for bottlers, as it contains starch in solution, and also some sulphate of lime, which influence disagreeably bottled beverages. It would not keep as well as the preceding two preparations, until preserved by the addition of about one-half drachm solution of salicylic acid, or about ten grains of peroxide of hydrogen, or one grain calomel.