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.
Loss of flavor is a mysterious disappearance only in resinous beverages, so far as our knowledge reaches, the ginger flavor in ginger ale being the principal one. Suggestions were invited and remedies requested by the trade. Mr. Taylor, an English chemist, to whom several bottles of flavorless beverage were submitted for investigation, after some disappointing researches, found at last nitro-compounds in the oil of vitriol, and instituted the following experiments: "Into a soda-water bottle were put suitable quantities of the ginger essence, syrup and calcium carbonate, and water to nearly fill it. Then sufficient of the contaminated acid was added to decompose the lime, and the contents of the bottle were immediately secured by a cork wired down. Repetition experiments were made, in which a portion of the ginger essence was replaced by capsicine and gingerine, and others in which a pure acid was substituted for the impure oil of vitriol. The bottles were opened at varying intervals, when the following observations were made. Those in which the impure acid had been used showed a marked decrease in pungency at the end of two hours; at the end of four hours the pungency was faint; at the end of six hours it had completely disappeared. The ginger essence, gingerine, and capsicine, had been affected apparently to the same degree. Those in which the pure acid had been used had retained their pungency apparently in its entirety.
"These results, which were in perfect accord with those which were obtained at the factory, left little doubt that the cause of mischief was attributable to the nitro-compounds in the oil of vitriol used for generating the carbonic acid gas. This conclusion received the clearest verification at the hands of the manufacturer the instant he used an acid that was free from smell, and that did not respond to the iron test".
This is a very valuable piece of information for the trade, and we beg to submit our own experiments and practical experience.
We started upon the theory that in storage and transportation the cane-sugar solution in the beverage has been, by the fruit acid, converted into the modification invert-sugar (see page 608 and following), with the aid of a high temperature, such as we experienced in tropical and subtropical climates, and that by converting the sugar solution, the resinous and gummy matter is also converted, and the caramel, which in its process of manufacture has passed the strata of inversion, is also affected, at least the latter was proved by the disappearance of color in all cases. Beverages prepared with genuine ginger extracts lost their flavor and color, while such prepared with essence of ginger oil lost their color also, but retained their flavor. Exposure of the beverages to higher temperature, acidulated with fruit acids for experimenting, became "inverted" and failed in flavor and color. We introduced in various samples small quantities of sulphuric, and in others nitric acid, and kept the bottles at ordinary temperature (in the temperate zone). The flavor and color were lost again. When we converted the syrup by boiling and the aid of fruit acids into invert-sugar before bottling, we had no more trouble, flavor and color kept permanent. Tests of inversion were applied in all cases with satisfactory results.
Non-inverted syrup (solution of cane-sugar) introduced into the beverage with ginger flavor and color, and the beverage kept at a low temperature, gave the same results. We considered our materials pure. From these experiments we came to the conclusion to use but invert-sugar for all ginger beverages - that is, to prepare the syrup or solution of cane-sugar exclusively by acidifying it with fruit acids, and did well by doing so.
Comparing our results with Mr. Taylor's, we beg to say that we experienced with nitric acid added to the beverage the same difficulties as he with the nitro-compounds in sulphuric acid, and therein we agree; but with pure sulphuric acid we got the very same effect, which leads us to believe that sulphuric acid, whether pure or impure, forced over by reckless charging or by imperfect purification of the gas, will bring about the same mischievous effect, viz. the loss of flavor and color. The gas no doubt contains and carries sulphurous, and when impure, also nitrous vapors, condensing them in the aqueous liquid. This in our opinion inverts the sugar and resin as both are readily inverted, especially by nitric or nitrous acid. We hope to throw by further experiments more light on this vexed matter, and would be glad to hear of more experimental results from our English cousin.
The remedies we suggest are but two. First, generating and charging very carefully and thoroughly, washing and purifying the gas, which will suffice for ordinary beverages; but secondly, to be more cautious and, especially for export or storage beverages, use only inverted syrup. These two remedies, we are convinced, if all the precautions against ropiness are observed, will preserve the ginger from all destruction.
Deterioration of beverages by oxidation of some ingredients, is, according to Mr. Warren (page 48), probably a cause for changes, especially in lemonade, caused by the oxidation of lemon oil. If this be verified, the careful expulsion of air from the water would be a remedy.