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.
In the preparation of syrups care should be taken to employ only the best refined sugar, which is free from impurities, and when dissolved in water is less prone to fermentation than partially refined sugar. When inferior sugar is employed clarification is always necessary. Distilled or filtered rain-water is recommended to be used, but there are no valid reasons against the employment of potable "Water that has been previously filtered.
The controversy over the proper method of preparing syrups for the manufacture of saccharine beverages is unending, and probably will always be a matter of contention with bottlers. Advocates for both the cold and hot process are not wanting. It is of great importance to use for Ordinary purposes as little heat as possible, as any solution of sugar, even when kept steadily at the temperature of boiling water (212° F.), undergoes slow decomposition. The reader will bear in mind the properties of sugar, and how it is converted at 320° and 338° F. into glucose and levulosan, and also under other conditions, by boiling, into convert-sugar (a mixture of grape-sugar and fruit-sugar), which is directly fermentable. But it is also of great importance to take into consideration that citric, tartaric arid acetic acids, so frequently employed in compounding syrups for the manufacture of saccharine beverages, convert a solution of cane-sugar even at ordinary temperature, The higher the temperature the more rapid is the conversion. Concentrated solutions (syrups) are completely inverted with considerable difficulty, but within the bottles the syrup is in a highly diluted state, which is again in favor of inversion. When inversion takes place within the bottled beverage, and the modification, "invert-sugar," is produced, the flavor and color of a beverage are impaired. Resinous matters are likewise inverted, and sugar colorings affected, which explains the "disappearance" of the "ginger-flavor and color," so frequently complained of. Gum foam, if of a resinous character, will be inverted also. When the inversion has commenced within the bottled beverage, a modification and rearrangement of the different components takes place, which generally results in separation, and precipitates or turbidity are the consequences. It depends entirely upon the purity and the character of the various constituents in how far these consequences will affect or destroy a beverage. The. inversion, when going on within the beverage, is the source of numerous complaints and inconveniences. We know it takes place under the influence of fermentation, or of the fruit acids added to the beverage. From these facts we must draw the following conclusions:
Fermentation we keep off by employing only pure material and by scrupulous cleanliness. Successful syrup-making depends foremost upon the freshness and purity of the ingredients, the intelligent care with which they are combined, and the cleanliness of the utensils employed. The inverting influence of the fruit acids we meet in several ways. We apply either the cold or hot process in preparing our syrups, as the kind of beverage may require.
1. For beverages containing fruit-acids, but intended for immediate consumption or within a limited time, and for those beverages into which fruit-acids do not enter at all, we recommend the cold syrup process, provided the sugar is of pure quality, as there is no immediate danger of inversion. However, in summer time, when the temperature is ex-tremely high and the beverages are prepared for shipment, exposed to the sun's rays and afterwards kept in country stores in crates for an unlimited time, we should prefer, for acidified syrups only, the next process as a precaution.
2. The hot syrup process, or, as we might also properly call it, "inversion process," we recommend to employ for the preparation of all beverages intended for storage or export into which fruit acids enter, also and particularly for all sparkling wines, cider, fruit-champagnes, etc.
We meet in this process the inversion of the sugar solution contained in the beverage by causing or hastening the inversion of the whole syrup while preparing it, and bring it to the modification of invert-sugar simply to prevent this modifying action from going on within the bottled beverage, which would have a destructive action upon it. The foremost point in the use and. treatment of sugar for the manufacture of acidified carbonated beverages, says Dr. Hager, is the application of a process that yields in the solution a clear and unchangeable modification (invert-sugar).
The inversion takes place on boiling the syrup with citric or tartaric acid. A practical method to complete this is to add the entirely necessary quantity of fruit-acid to the mixture of sugar and water, and bringing the mixture to a boil, then filtering and clarifying it. Hager recommends the addition of six ounces either citric or tartaric acid crystals (or three ounces of each) to every twenty pounds of sugar. The corresponding quantity of fruit-acid solution may be used instead. In case these proportions, are used, a deficiency of fruit-acid has to be corrected when compounding the syrup. But if this inverted syrup is for immediate use, we recommend to boil the syrup and acid slowly together for some time, occasionally adding some water in order to make up for the loss by evaporation, and keeping the syrup at its standard strength. Syrup thus prepared is rapidly inverted, and should then be filtered and clarified, when it will be ready for use.
A suggestion we prefer to make here, in case aniline colors are employed in coloring a syrup, is to use citric acid exclusively, as tartaric acid interferes with that color and would cause it to disappear.
By following this inversion process we simply do in advance, or start artificially, what in the course of time would happen in the bottled acidulous beverage, thus contributing towards or assisting its preservation. The inverted syrup will have lost a fraction of its sweetness, but any deficiency is made up by using a trifle more syrup if desired. When the beverage is properly prepared and charged with carbonic acid gas, it will keep unaltered for an indefinite time.