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.
Syrups should be perfectly transparent. The act of clearing or making the syrups bright by chemical or mechanical means, or the separation of all foreign substances which may disturb its transparency, is the "process of clearing," instead of filtration. Usually clarification is combined with filtration. When refined cane-sugar is used, filtration as formerly directed will be found quite sufficient, and one of those filters, or those attached to the syrup-making plants, described, are practical contrivances. When an inferior grade of sugar is used, or exceptional precaution is desired, clarification is resorted to.
The chemical means are albumen, - white of egg or patent (artificial) albumen - or granulated animal charcoal. Albumen combines with the liquid when cold, but on the application of heat rapidly coagulates (at 70°C. or 158°F.), and rises to the surface, carrying the impurities with it, forming a scum which is easily removed with a skimmer. It is therefore used for clarifying syrups prepared by the hot syrup process only, and should never be employed with the cold syrup process, as it would remain in solution if not coagulated, and produce in course of time fermentation. Animal charcoal acts as a decolorizer, purifier and strainer; it corrects a defective refining of sugar, and is especially employed where inferior sugar is used. It is added to the mixture of sugar and water, and the whole heated either to the simmering or boiling point, as preferred, while stirring. When the syrup is done it is advisable to allow time for the charcoal to subside, as the accumulated charcoal in the filter would not permit a quick filtration. If the syrup is prepared by the cold process, and animal charcoal is preferred for its clarification, it is best to dissolve the sugar in the water by agitation and afterwards stir the charcoal in, agitating the mixture repeatedly, and then allow the charcoal to subside, when the syrup should be filtered; or filter the syrup through a layer of charcoal. Bone-black (char-coal-dust) should never be used. Animal charcoal can never be used at all with flavored syrups as it would absorb the flavor. The proportions of albumen or animal charcoal should be as follows: for twenty pounds of sugar the white of one egg, or 2 drachms patent albumen instead; the proportion of granulated animal charcoal should be about five pounds.
The mechanical means are also granulated animal charcoal, which acts both chemically and mechanically. Other means employed are the following: