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.
Besides the filter-bags and other arrangements for filtration, described in Chapter XXVI (Filtration And Clarification Of Extracts, Essences, Etc)., which serve in all cases also as clarifying apparatus where any clarifying substance has been employed, still special arrangements for clarifying plain or compound syrups have been proposed. Tin or porcelain lined or stone-ware vessels (none of wood should be employed) are recommended, with a perforated bottom, a close-fitting circular piece of felt on it, a layer of glass-sand, etc., and on top of the latter felt or flannel again. The syrup is poured in at the middle, when the layer of filtering material will not be disturbed and no channels will form. When compound syrups are to be clarified, each kind requires a separate apparatus. An arrangement of this kind, when the layer of sand is thick enough to be effective, that is, to retain impurities, will either stop the passage of concentrated syrups, or at the best permit a slow passage, which, even if the operation is constantly carried on, will not prevent syrup from crystallizing; and as such a filter cannot be hurried in its work, it is for practical service not much applicable where the quick and effective filtration and clarification of considerable quantities has to be accomplished.
Clarification with the aid of the flannel or felt bag or a similar arrangement, and with those different clarifying agents specified, is for practical purposes the best method. When any of the clarifying mediums is allowed to at least partly subside, it will precipitate most impurities and the syrup will run fast and bright through the filtering bag.
Re-clarification can be combined if desired by simply arranging another filtering bag beneath the first one, so that the syrup is compelled to pass through it also before flowing into the syrup receptacle. A second application of clarifying material is quite unnecessary; and even this re-clarification is but with inferior syrups required.
A proper custom is to pour back the first runnings of a filter to ensure their thorough clarification. This should always be done, and answers satisfactorily.