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 great popularity of the Belfast ginger ale is principally due to its fine aroma. All carbonators strive to imitate it as closely as possible, but it is an unfortunate fact, however, that a great deal of American ginger ale is "miserable stuff," in many instances nothing more than sweetened water.
In properly combining various flavors and creating a new harmonious single aroma, lies the secrecy of manufacturing ginger ale, be it made in Belfast or anywhere else; but sometimes the flavoring is so strong, added to such an excess, as to rob the beverage of its chief merit - the ginger itself. Although the latter, pure and simple, is not always an agreeable mixture to many, the introduction of other and more pleasant flavorings adds immensely to the quality of ginger ale.
The Belfast ginger ale is not fermented, consequently is not alcoholic. It is sparkling and clear and has a most agreeable odor, is free from intoxicating qualities, yet is warming and invigorating. It is pleasant to taste and has a delicious "bouquet".
The exact composition of this beverage is not generally known, but it is understood that ginger, capsicum and lemon and citric acid or lime juice are the chief flavoring ingredients. Into the combination enter also some of the other flavorings recommended for ginger ale in quantities judiciously selected. Some flavor of rose that enters undoubtedly gives the Belfast ginger ale that bouquet closely resembling attar of rose. The addition of some oenanthic ether gives it no doubt that rich, pungent, vinous odor thrown off by this ether, and imparts a smoothness to the "beverage of which it forms a part, and a fruity, pleasant bouquet. A few drops of oenanthic ether, previously dissolved in alcohol (essence of oenanthic ether), added to the ginger-ale syrup - or, better, one to two drachms added to the ginger-ale extract or soluble essence - will be the proper quantities.
It is held by some of the best known carbonators, that the addition of lime juice to ginger ale imparts a rich fruity quality acquired in no other way Necessarily a lime juice free from mustiness, and carefully filtered, should be employed. The quantity to be used is at the discretion of the bottler, whose taste is his only criterion.
The selection of a suitable quality of ginger, the obtaining of pure alcohol, the regulating of the extracting process, and the addition of the proper amount of capsicum, lemon, rose, cinnamon, or other flavors - these are operations that require a thorough experience with all the rules and laws of compounding. All ginger extracts improve with age; it is therefore advisable that bottlers who make their own should keep a year's supply ahead, so that none need be used until at least a year old.
It will be observed that the genuine Belfast ginger ale is put up in round-bottomed bottles, closed with metallic caps and annealed wires. The round bottom tends to insure a position of the bottle that keeps the cork moist, and with the aid of a fine grade of cork, and furthermore with the aid of the cap, it is made practically certain that the contents "will not be spoiled by the escape of the carbonic acid.