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 use of adulterants in flavorings has grown rapidly of late years. Formerly it was confined chiefly to the addition of tonka beans to vanilla, extract of geranium to rose, and of cherry to almond. Now, what are known as "compound ethers" or "artificial fruit essences" are largely employed as adulterants. These others are frequently of great strength, a single drop sufficing to give odor and flavor to a gallon of fluid.
Care should be taken in pre-paring mixtures of essential oils that fine and ordinary oils are not used together; neither should the oils used be such that the odor of one will cover that of another, or neutralize it. Oil of anise is very much used with oil of caraway, oil of lavender, oil of cassia, oil of peppermint, oil of rosemary, etc. Those oils all harmonize with the oil of anise; but the latter must not be used in too large quantity. Anise oil readily solidifies at low temperatures, and then has a peculiar crystalline appearance.
The home-made compound essences, composed of various flavors, improve by age as well as the plain essences, and thereby become "harmonious;" they therefore should be prepared for a long time in advance, but by rectification this improving process can be hastened and on a small scale the appended engraving, a glass retort on a sand bath, is a very practical apparatus. The essences or compound extracts are usually shaken with pumice or glass sand in order to remove and precipitate any resinous matter, and the whole mixture is introduced into that retort and distilled until two-thirds or three-fourths of the original liquid has been received, which is the rectified or refined preparate, the balance being used at the next operation.'
Fig. 423. - Glass Retort on a Sand Bath.
This process will produce a harmonious flavor, and is carried out on a larger scale with the stills represented by Figs. 402 and 407.