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 desired quantity of sugar or glucose, say thirty pounds, and one of carbonate of soda or potash, or one and one-half pound of carbonate of ammonia,' are put into an iron kettle, as hereafter illustrated, and heated over a free and strong fire until completely melted, and showing a light or reddish coloration. Stirring up to this point is not necessary. It is erroneous and superfluous to saturate the sugar with some water at the beginning, as some bottlers use to do; it prolongs unnecessarily the operation, since the water has to be evaporated before the sugar commences to melt, and its admixture is of no advantage. The melted sugar presents a homogeneous mass As soon as it appears dark brown and white, suffocating vapors are arising, which make the eyes tear; and large bubbles appearing on the surface of the mass, the fire must be reduced and the mass constantly and vigorously stirred with an iron spatula as illustrated hereafter, to prevent the mass becoming charred at the bottom and divide the heat equally. At this stage of the operation the mass rises considerably and expands to about four times its volume - 'therefore the kettle must have enough capacity to hold at least four times the volume of sugar or its substitute. While the mass becomes darker, or when it has become dark, apply the following tests to ascertain the finish of the operation: 1, take with another spatula (continuing stirring with the first) some out of the hot mass and let it drop back; if the mass appears in threads, which appear whon held against the light transparent, intensely dark red-brown, it is done, and the color ready; if the threads appear reddish, boil longer; or 2, let fall a few drops of the mass from the spatula into cold, clear water, and remove them when cold; if they are hard and crack between the teeth, are not sticky, and have a faintly bitter taste, the color is done, otherwise prolong boiling; or 3, let a drop of the mass fall on a cold glass plate, where it will quickly crystallize to a porous glass-like mass; if it appears black, or the edges brownish transparent, and does no more taste sweet, but is tasteless or has a faintly bitter taste, it is done, else continue to a finish.
The alkalies are usually and previously dissolved separately and the solution added to the sugar or glucose; or they may be put first in the kettle and heated with an equal volume of water until dissolved and then the sugar or glucose be added to the kettle.
While this operation is going on, heat in another kettle sufficient water to dissolve the sugar coloring. The water must be hot or boiling, and ready the moment the coloring is done. Use no cold water. When the last decisive taste is made, and while constantly and vigorously stirring, immediately pour the hot water in a thin stream into the coloring, when the latter will be immediately dissolved. Great care must be taken not to overheat the sugar,and to add the water at the proper moment, as a large quantity of huminic acid would be formed, which has not been neutralized by the small quantity of alkali or carbonate of ammonium that has been previously added, and which being insoluble and suspended, or separating only after a long time, would make the coloring unfit for proper use or cause sediments in the beverages or liquids to which it is to be added. If the mass is overheated to excess it will suddenly turn into insoluble sugar-coal.
The quantity of water employed for dissolving the caramel varies in proportion; a fourth, a third, a half, or even an equal amount of water to that of the sugar used, is added according to the concentration desired.
It must, however, be borne in mind, that most always small quantities of sugar and its mechanical impurities become charred and thereby insoluble, and that these particles cannot entirely be removed by subsequent nitration from the concentrated liquid, and would afterwards cause precipitate and sediments in the aqueous carbonated beverages. It is therefore advisable, either to dissolve the coloring in a half or an equal quantity of water, allow time for subsidence of the suspended and insoluble charred matter, decanting and filtering the supernatant liquid through a felt bag, and, evaporating to the desired consistency in vacuo or over a water bath, or filter the dissolved coloring while still hot through a flannel bag, and before use, dilute the necessary quantity with an equal volume of water and filter again. The former method is followed in wholesale manufacturing, while the.latter is adapted for home-use; but these precautions are absolutely necessary to prevent sediments of charred and other insoluble matters in the beverages. A well-made sugar color should have no sweet taste, and be perfectly clear in water.