Sirops, Fr. Cod.; Sirupi, P. G.; Sirupe, G.; Sciroppi, It., Jarabe, Sp.
Syrups are concentrated solutions of sugar in aqueous fluids, either with or without medicinal impregnation. When the solution is made with pure water, it is named syrup or simple syrup; when made with water charged with one or more medicinal agents, it is called in general terms a medicated syrup, and receives its special designation from the substance or substances added.
Medicated syrups are prepared by dissolving sugar in infusions, vinegars, decoctions, expressed juices, fermented liquors, or simple aqueous solutions, or by adding a medicating substance, like a tincture or a fluidextract, to simple syrup. When the active matter of the vegetable is not readily soluble in water, is associated with soluble matter which it is desirable to avoid, or is volatilized or decomposed by a heat of 100° C. (212° F.), it is sometimes extracted by diluted alcohol, the spirituous ingredient of which is subsequently driven off.
The process of percolation has been applied for the solution of the sugar and is offered as an alternative process in a number of official preparations. This process offers several advantages over the older methods. The amount of labor attending the operation is greatly reduced, no heat is employed so that volatile constituents are not injured, and the finished syrup is filtered and protected from the usual contaminations attending straining, etc.
The quality and quantity of the sugar employed are points of importance. Official granulated sugar should be employed and although the commercial grades are usually of good quality it is possible to secure a sugar of better grade, known as "druggists' dry granular" or "crystal A," which is obtained from the first runnings from the bone-black filters. In this sugar the crystals are large and the syrup is unusually free from yellowish tint, even in a heavy strata. The syrup made from this sugar is often sold as "Rock Candy Syrup."
In relation to the quantity of sugar, if in too small proportion, fermentation is apt to occur; if too abundant, crystallization. The Pharmacopoeial formula calls for 850 Gm. of sugar to make 1000 mils of syrup, the amount of water required being about 465 mils. A somewhat smaller quantity will answer where an acid, such as lemon juice or vinegar, is used.
As it is desirable, in many instances, that the active matters should be in as concentrated .1 state as possible in the syrup, it is often necessary to evaporate a large proportion of the aqueous fluid in which they are dissolved. This may be done either before the addition of the sugar or afterwards. In either case care is requisite not to apply a heat too great or too long continued, lest the active principles should be injured. The use of concentrated pharmaceutical preparations, such as tinctures and fluidextracts, as the source of medication, has largely replaced other methods. The proper point of concentration for syrups which are prepared on a large scale by boiling is best ascertained by the use of that variety of Baume's hydrometer called a saccharometer. This should stand at 30° in boiling syrup—30.5° in hot weather and at 35° in the syrup when it is cool. Another very accurate, though less ready, method is to ascertain the sp. gr. by weighing a portion of the liquid. Syrup, when boiling, should have a sp. gr. of about 1.261; at 25° C. (77° F.) about 1.313; this is the specific gravity of the official syrup. A third method of ascertaining the proper point of concentration is by the thermometer, which, in boiling syrup of the proper consistence, stands at 105° C. (221° F.). This indication is founded on the fact that the boiling point of syrup rises with the increase of its density.
When carefully prepared with the best refined sugar, syrups made by the hot process or by agitation in the cold usually require no other clarification than to remove any scum which may rise to their surface upon standing, and to pour them off from any dregs which may subside. But, as the sugar employed is seldom free from impurities, it may be best, as a rule, to remove the scum as it rises during the heating process, and to strain the syrup while hot through muslin or flannel. The percolation process avoids this necessity. Should syrups at any time lack the due degree of transparency, they may be filtered through paper if a hot water funnel is used, or, when likely to be injured by this treatment, may be clarified by other mechanical means, as mentioned under the head of Syrupus. The vicious habit practised not long ago by sugar refiners of "blueing" sugars by the use of ultramarine and other coloring agents cannot be too strongly deprecated, and it is a great benefit to pharmacy that this practice has been discontinued by most sugar refiners. (See A. J. P., 1901, 119.)
The medicated syrups are liable to undergo various alterations, according to their nature and mode of preparation. The acid syrups, when too much boiled, often show a copious white deposit, which is invert sugar produced by the action of the acid upon the sugar. Even at ordinary temperatures, acids slowly convert common sugar into invert sugar, which, being less soluble than the former, is often deposited in the form of crystalline grains. Excessive acidity soon causes a darkening of the syrup, due to caramelization of the sugar. Syrups containing too little sugar are subject to fermentation, in consequence of the presence of yeast cells. Those which contain too much, deposit a portion in the crystalline state, and the crystals, attracting the sugar remaining in solution, gradually weaken the syrup, and render it liable to the same change as when originally made with too little sugar. The want of due proportion of saccharine matter frequently also gives rise to mouldiness, when air has access to the syrup. It is said that syrups enclosed, while they are still hot, in bottles which are not full are apt to ferment, but if in well filled bottles they will generally keep better. When syrups undergo the vinous fermentation, they become covered at the surface with froth, produced by the disengagement of carbon dioxide, and acquire a vinous odor from the presence of alcohol, while their consistence is diminished by the loss of a portion of the sugar, which has been converted into that liquid. When the quantity of alcohol has increased to a certain point, the fermentation ceases, or goes on more slowly, owing to the preservative influence of the alcohol. Such syrups should never be used for pharmaceutical purposes, as no amount of rebelling can render them fit for use.
The percolation method for preparing syrups has come into general use. For some syrups it is to be preferred to the usual method of heating, and all syrups which contain a volatile principle, or one likely to be injured by heat, are preferably made by percolation. L. Orynski (D. C., March, 1871) first drew attention to the subject. The details of the official method are given below. It was first recommended that a small piece of sponge should be used to close the lower orifice of the percolator, but this has advantageously been replaced by purified cotton. Some experience is necessary in adjusting the cotton, but the proper degree of pressure is soon learned.
To be successful in using the process, care in several particulars must be exercised. (1) The percolator should be cylindrical or semi-cylindrical, and cone-shaped as it nears the lower orifice. (2) The sugar must be coarse, else it will form into a compact mass, which the liquid cannot permeate. (3) The sponge or pledget must be introduced with care. If pressed too tightly in, it will effectually stop the process; if inserted too loosely, the liquid will pass too rapidly, and will, in consequence, be weak and turbid (not properly filtered). See also a practical paper on this subject in A. J. P., Jan., 1881, by G. H. Chas. Klie, and Bull. Pharm., 1902, 1248. For a paper on Fruit Syrups, see West. Drug., 1902, 182; Proc. Penn. Pharm. Assoc., 1903, 196.
Syrups may be made (without heat) rapidly by putting the ingredients in a churn and agitating briskly.
"Rock Candy Syrup," the evaporated mother liquor left after crystallizing sugar in the form of large crystals, called "rock candy," has come largely into use in America. It varies much in quality as made by various manufacturers, and often contains added glucose. It should never be used indiscriminately or for making the official syrups, and it should always be carefully tested before being used for any purpose. (See analyses by L. F. Kebler, in A. J. P., 1895, 143.)
At best, syrups are apt to change, and various measures have been proposed for their preservation, but the best plan is to make small quantities of syrups at a time, and to keep them, unless when wanted for immediate use, in bottles quite full and well stoppered, which should be put in the cellar or other cool place. Glycerin is often used to aid in the preservation of syrups; in special cases this may be advantageous, but the solvent properties of glycerin must be remembered, and the finished preparation may possess properties (due to the glycerin) which are not found in syrups made without glycerin, and which may therefore be injurious in prescriptions. (See West. Drug., 1898, 444.)