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 National Dispensatory gives the following on the preparation of syrup: "Most syrups of the United States Pharmacopoeia are now directed to be made by dissolving the sugar in the proper liquid without heat, with the view of avoiding the evaporation of volatile ingredients and the inverting influence of hot acid liquids upon the cane-sugar. L. Orynski (1871) proposed to extend this process to all syrups, and the method has been found by R. Hunstock (1875) and others not only much easier and more economical than the officinal process, but likewise to yield syrups which, as a rule, are less liable to ferment. This latter quality may probably be directly referred to the avoidance of heat, since the continued application of heat is known to produce changes in the sugar resulting in the formation of glucose. Simple syrup, made by dissolving the sugar at the boiling-point very soon after it has been prepared, reduces alkaline solutions of copper, showing the formation of grape-sugar, while simple syrup made from the same sugar, but without heat, forms grape-sugar more slowly. This so-called cold process for preparing syrups therefore deserves attention. If made with aqueous infusions of drugs, such syrups will contain the soluble albuminous principles, and probably not be quite as unchangeable as those prepared with the aid of heat; but if the drug has been exhausted by an alcoholic liquid, as directed by the United States Pharmacopoeia for most of the syrups to which these remarks apply, albumen is not present.
If heat is employed, as directed by the pharmacopoeias for most syrups, the loss occasioned by evaporation should be rectified by the addition of water. This is easily accomplished by taking the weight of the vessel with its contents before and after boiling, and adding enough water to compensate for the loss occasioned by heating. The proper portion of sugar to menstruum ensures the stability of the syrup. Should the sugar be deficient in quantity it could not sufficiently protect the other organic principles contained in the syrup, and it would be liable to ferment. On the other hand, if too much sugar be employed, the excess would crystallize after cooling, and dispose an additional quantity to separate in a like manner, thus leaving the syrup weaker in sugar than it should be, and subject to similar alterations, as if an insufficient quantity of sugar had been used. The proper proportion of sugar is a little less than twice the weight of water, or thirty-five parts of water to sixty-five parts of sugar, as directed by the United States Pharmacopoeia for simple syrup. For colder climates a little more water may be employed; the German Pharmacopoeia directs forty parts of water to sixty parts of sugar. If the liquid contains already much organic matter in solution, or if it is partially alcoholic, a correspondingly smaller amount of sugar will be required".