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.
At the present time salicylic acid occupies the foremost position as a preservative, and testimonials are not wanting which favor its continued employment, whilst from many sides we are warned against its use and its harmful effects, and even authorities have condemned its employment. Let us consider this mixed-up matter, and first get acquainted with the properties of salicylic acid and its origin. Salicylic acid exists ready formed in flowers of spiraea ulmaria (meadow-sweet), and as methyl salicylic ether in oil of wintergreen. It can be prepared from indigo, and from salicin, a substance found in the bark of several species of willow and poplar. For commercial purposes it is prepared from phenol, carbolic acid, one of the products of the destructive distillation of coal. The fact that phenol or carbolic acid is one of the most powerful preservatives known, led Kolbe, its inventor, a German chemist, to believe that salicylic acid might be possessed of the same qualities, and, as it is an odorless, almost tasteless, and, when taken in small quantities, innocuous body, it would prove of great value. The result showed that Kolbe's surmises were correct. Experiments were made on articles of food and on beer, and very small quantities were found to check the fermentation of yeast. Its action on preserving beer and carbonated beverages was well marked, and it is largely used for that purpose by many brewers and bottlers. It is a snowy white, flaky powder when pure, slightly soluble in water. There are some bottlers who find great benefit from its use. Its valuable properties as a preservative have the further advantage that it is odorless and tasteless.
Salicylic acid or salicylates are habitually added to a number of articles of food or drink with a view of preserving them from fermentation and putrefaction. Salicylic acid as a preservative cannot be relied upon when brought into contact with any liquid substance in wooden vessels or casks. The salicylic acid under these circumstances speedily disappears, being apparently absorbed and decomposed by the wood tissue. When this acid is used as an addition to beer or wine, the cask must first be coated with pitch. Contact with iron or other metallic vessels is to be avoided, since a reddish color is thereby imparted.
The value of salicylic acid is due, not only to the faculty it possesses in a high degree of exercising a destructive effect on these organisms, of preventing their development, or arresting the decomposition that may have already commenced; but to the fact that at the same time it is claimed to exercise positively no effect on the nature or components of the substance with which it comes in contact. It has found introduction into the most varied fields. Of peculiar interest, however, are the results that have followed the utilization of salicylic acid in the preparation and preservation of beverages, and in no other trade has it found so versatile, so practical, and so well-developed employment, or proved itself so valuable as a reliable aid in working operations, as in the bottling business. The result of a continuous use of salicylic acid has been made the subject of numerous investigations, and it has been found that even when taken daily, in considerable quantities, it exercises no injurious results when taken in such small quantities as it is used in the preservation of beverages. On the other hand, reliable authorities, while freely admitting its antiseptic and preservative characteristics, are doubtful of its harmless effects. It is said to bring on nervous disorders, impotency, and other unpleasant complications. How far it is injurious to the human system when absorbed in small quantities, scientific authorities differ; but it must be said that all official investigations into the character and effect of salicylic acid, as used in drinks or food, have been followed by its unqualified condemnation, if not prohibition. There can be no doubt that in large quantities it acts injuriously.
At the present time salicylic acid is employed in carbonated drinks almost to the exclusion of anything else, and, so far as we know, no deleterious effects have followed. The prejudice against salicylic acid in many cases is due to an impure preparation. However, one fact is certainly established beyond a doubt, namely, it is not quite satisfactory; and the time may come, when, as in France, it will be prohibited.