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 filtration of syrups is now generally effected on the large scale by passing them through the arrangement just described. On the small scale, as employed by bottlers and druggists, they are usually passed through conical flannels or felt bags. (See Figs. 363 and 364.) The filtration of very thick syrups is, however, attended with some difficulty, and it is therefore a good plan to filter them in a somewhat dilute state, and afterwards to reduce them to a proper consistence by evaporation in clean vessels of tinned copper,' by steam heat. Syrups, when filtered in a heated state, run well for a time, but the pores of the fabric rapidly get choked, from the thickening of the syrup and partial crystallization of the sugar, occasioned by the evaporation of the aqueous portion from the surface of the bag. This may be partially prevented by enclosing the bag in a metallic casing, or employing the so-called patent rapid filter illustrated by the annexed engraving or by changing the filter when choked.
A practical syrup filter, well arranged for protecting syrups during and after the process of filtration, is illustrated by the next engravings, and by the syrup-making plant appended later on. The usual filtering bag is used, but the weight of the syrup to be filtered from an elevated kettle is utilized to get additional pressure.
Fig. 375 explains the parts. A A is a filter bag, attached to a ring D. B B is a tinned copper tube, firmly attached to the ring C. It is fitted with three clamps F, which are used to secure the tube B B to the disc E E, as shown more clearly in Fig. 374. G is a bracket that carries the filter. The filter bag is secured by the clamp between the disc and the tube, so as to make a water-tight joint.
The illustration is the so-called "Lightning syrup filter, Favarger's patent, England.
In pouring the syrup into a filter, the stream should be directed into the middle and not upon the sides, so as to avoid disarranging the felt, which would interfere with the success of the operation.
After every operation the filters should be carefully washed with hot water and dried, if not continued in use.
The same filter may be used for various syrups and other thick compounds, but it is usual to have different frames and cloths for different flavors. A ball cock can be fixed in the upper part to regulate the inflow.
Fig. 373. - Cased Syrup Filter.
On the whole clarification is preferable to filtration for syrups on a small scale. They need only be treated with a little white of egg, or commercial albumen. When heated a scum rises (the albumen coagulates at 70° C), which must be removed as soon as it becomes consistent, and the skimming continued until the liquid becomes clear. Any floating portions of scum that may have escaped notice are easily removed by running the syrup through a coarse flannel strainer, whilst hot. The most extensive application of the process of filtration in the arts is in the refining of sugars.
Later on we shall explain the modes of preparing syrups, and append a full plan for preparing and filtering it on a large scale, especially for the purpose of making beverages.
Fig. 374. - Metal Cask Syrup Pressure Filter.
Fig. 375. - Sectional View of Fig. 374.