Syrups

Syrups are concentrated solutions of sugar in water or other aqueous liquid. There are three kinds of syrups.

1. Simple Syrup: concentrated solution of sucrose in purified water alone.
   
   
2. Medicated Syrup: aqueous solution of sucrose containing added medicinal substances and in addition to sucrose, certain other polyols, such as glycerin or sorbitol may be added to retard crystallization of sucrose or to increase the solubility of added ingredients.
   
   
3. Flavored Syrup: contains various aromatic and pleasantly flavored substances and is intended as a vehicle or flavor for prescriptions. This flavored syrup are preferred particularly for children because of the absence of alcohols or very little alcohol they contain and this makes them superior solvents for water-soluble substances. They possess remarkable making properties for bitter and saline drugs.

In the manufacture of syrup, the sucrose must be white crystalline variety commercially known as granulated sugar. A purified water free from foreign substances and clean vessels and containers must be used.

The concentration of sucrose approach but not quite reach the saturation point. Dilute solutions of sucrose provides an excellent nutrient for mold, yeasts and other microorganism. Concentrations of 65% by weight or more of the solution will retard the growth of microorganism, however saturated solution may lead to crystallization of part of the sucrose under conditions of changing temperature.

When heat is used it is almost certain to have an inversion of a slight portion of the sucrose.

C₁₂H₂₂O₁₁               →                 2C₆H₁₂O₆

Sucrose                                        Invert sugar

The invert sugar are dextrose and levulose. Invert sugar is more readily fermentable than sucrose and tends to darken the color, however the 2 reducing sugars are of value in retarding the oxidation of other substances. Levulose formed during inversion is sweeter than sucrose, thus resulting in syrups that are sweeter and is responsible for the darkening of syrup. Overheated syrups or sucrose caramelizes.

Methods of Preparing Syrups

Four methods are employed in making syrups. The choice depending on the physical and chemical characteristics of the substances entering into the preparation:

1. Solution by heat
2. Agitation without heat
3. Addition of medicating liquid to syrup
4. Percolation

Solution by Heat

This method employs when the valuable constituent is neither volatile nor injured by heat and when syrups are to be prepared rapidly. Sucrose is added to purified water or aqueous solution and heated until solution is effected, strained and sufficient quantity of purified water added to make the desired volume or weight. Syrups made from an infusion or decoction, or an aqueous solution containing albuminous matter which is eliminated by straining. Albumin or other impurities permitted to remain in the syrup, will induce fermentation in warm weather.

Excessive heating of syrups to boiling temperature, is undesirable since more or less inversion of sucrose occurs with an increase tendency to ferment. Syrups sterilized in an autoclave caramelizes which is indicated by a yellowish or brownish color.

Agitation without heat

Used in cases where heat would cause the loss of valuable volatile constituents. In quantities up to 2000ml or 2 quarts, the sucrose should be added to the aqueous solution in a bottle of about twice the size required for the syrup. This permit active agitation and rapid solution. A “five-pint”, glass stoppered tincture bottle is well adopted for making one liter of syrup by this process. Stoppering of bottles prevent contamination and loss during the process. The bottle should be allowed to lay upon its side when not being agitated. For making syrups of large quantities the glass lined tank with mechanical agitators are specially adapted to the dissolving of sucrose.

Addition of a medication liquid to syrups

This is employed in those cases where fluidextract, tinctures or other liquids are added to syrups to medicate it. These syrups usually developed precipitate because the resinous and oily substance dissolved by the alcohol precipitates when mixed with syrup (contains water) producing unsightly preparation. This has been modified by mixing the fluidextract or tincture with water, allowing the mixture to stand to permit separation of insoluble constituents, filtering and dissolving the sucrose in the filtrate. This is not permissible when the precipitated ingredients are the valuable medicinal agents.

Percolation

This procedure consists in permitting the purified water or aqueous solution to pass slowly through a bed of crystalline sucrose, to dissolve it. The neck of the percolator is moderately plugged with a pledget of cotton and water or aqueous solution added, the flow of solution is regulated by a suitable stop-cock so that drops appear in rapid succession. If necessary a portion of the liquid is repass through the percolator to dissolve all the sucrose. Finally sufficient quantity of water is allowed to pass through the cotton to make the required volume.

Pointers for a Successful Preparation of Syrups Using Percolation Method

1. Percolator used should be cylindrical or semi-cylindrical, or cone-shaped as it nears the lower orifice.
2. Coarse granular sugar must be used, or it will form into a compact mass, so that the liquid cannot permeate.
3. Purified water must be introduced with care. If inserted too tight will stop the process; if to loose, the liquid will pass too rapidly and will, in consequently, be weak and turbid (from imperfect filtration) the cotton should be inserted completely within the neck of the percolator, since a protruding end, inside the percolator, up through the sucrose will permit the last portions of water to pass out at the lower orifice without dissolving all the sucrose.

Preservation of Syrups

Where special facilities cannot be employed for preservation of syrups, they should be made only in small quantities that can be used within a few months.

There are several ways of preserving syrups:

1. Low temperature not above 25^oC.
2. Concentration without supersaturation.
3. Addition of preservatives to prevent bacterial and mold growth – e.g. glycerin, methyl parabens, benzoic acid and sodium benzoate added particularly when concentration of sucrose is syrup is low.
4. For fruit syrups: A number of bottles which hold not more than pint are cleaned thoroughly and kept hot by immersion in boiling water until ready for use and a sufficient number of corks, thoroughly soaked in hot, purified water and of the proper size for the bottles should be at hand. Syrup should be heated to the boiling point (strained if necessary and reheated) poured into the hot bottles until they are fill to the brim. Corks are forcible pressed into the necks of the bottles, thereby displacing a small portion of the syrup and tied down with twine or wired in place. While the necks of the bottles are still hot (and before the syrup can contract in volume through cooling) they are dipped into melted paraffin contain in a suitable vessel. By this method organisms which produce fermentation are destroyed by the heat, and no air carrying new contamination, can find its way to the syrup, as the bottles are hermetically sealed.

Officials syrup should be preserved, in well-dried bottles, preferably sterilized. The bottles should hold not more than is likely to be used during 4 to 6 weeks should be completely filled, carefully stoppered, and stored in a dark place.