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.
To make a high-class ginger ale it is absolutely necessary to use water which is absolutely free from lime and magnesia. If the water contains much lime or magnesia and is used for a beverage containing resin, like ginger ale, and if no fruit acid be used, it will form some kind of a lime or magnesia soap, stringy, slimy and of a cloudy appearance; if tartaric acid be used, it will unite with the lime or magnesia and cause a precipitate which in either case looks unpleasant and disagreeable, and often becoming unpalatable. We have already expressed this opinion in another part of this work, but deem it important to recall it here again.
The bottler will find it to his advantage, in the preparation of a high-class ginger ale, to use only boiled water from which any precipitate has been allowed to subside. This water contains no air, and when being charged with carbonic acid takes up or absorbs more gas, and can therefore be charged with fully sixty to seventy pounds of gas. No higher charge should be made, as the gas expands on rise of temperature and would surely burst the bottles. To preserve ginger ale a solution of salicylic acid is usually added, generally two drachms to each gallon of syrup.
Another way to preserve bottled ginger ale is to steam it. The following steamirg operation has been recommended by Mr. W. F. Roorbach in the National Bottlers' Gazette: "Have a square tub with a tight-fitting lid to prevent the escape of the steam. Place bottles in the tub and fill it with cold water, and let it cover about two-thirds of the bottle. Turn on the steam and bring it up slowly to about 180 to 190 degrees by the thermometer, and keep it there for about five or ten minutes. Take out the bottles while hot, and turn upside down to prevent the escape of the gas. In this way some of the gas is lost - escapes through the cork while being heated - but there is plenty left in the bottles when finished to make a good ginger ale. Ginger ale made by this process can be relied upon to keep in any climate and for any length of time as far as the water and syrup is concerned. But as to the flavor of the ginger ale and keeping, all will depend upon the extract used, which should be soluble goods. I have known the ginger ale to be in fine condition two years after being bottled, both in appearance and flavor, by the above process. The sediment can be disposed of by 'fining' down".
We have nothing to add to this process, and have taken it up being a practical proposition. However, when the extract and soluble ginger-ale essence is prepared with all that care we have suggested, when then the syrup is well blended, boiled water exclusively used, a ginger ale can be made that keeps equally long.