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.
As already stated, sugar coloring may also be prepared from molasses or glucose, furnishing a coloring that answers for all purposes; to use cane-sugar is therefore rather a luxury. But not all glucose is suitable for making coloring. If it contains large quantities of dextrine it is unfit; small quantities may he permitted without consequences. Dextrine in glucose is detected by dissolving some of the suspected glucose in water; add of this solution one to three drops to some absolute alcohol in a test tube, and shake the mixture. If white flakes separate, dextrine is present in glucose; from the intensity of this separation the degree of admixture may be judged - if but slightly, the glucose may be used; should, however, the whole liquid become turbid, the glucose should be rejected. If blue litmus paper is dipped into a solution of the glucose and turns red, a considerable quantity of free acid may be suspected, if it turns only violet, but traces of it are present.
However, even glucose that contains sulphuric acid can be employed for making sugar coloring. If only traces are present it should be used unhesitatingly, as it is difficult to obtain glucose entirely free from traces of sulphuric acid, and mere traces are neutralized by the alkalies that are to be added. Crystallized glucose (grape sugar) is usually purest, while the liquid part or syrup contains dextrine in various proportions. For making sugar coloring nothing but well purified and filtered water should be used. The boiling of the water, previous to its use for dissolving the color, is usually sufficient to purify it from most of its impurities, so that it then can be unhesitatingly used.
The storage of sugar coloring requires not much attention and no particular care. The sugar lost, by being converted into caramel, the conditions necessary for fermentation, and the sugar coloring can, therefore, be stored in any suitable room, on a larger scale in closed or covered casks or tanks, small quantities in demijohns, etc.; whiskey barrels are highly recommended.