Several samples of so-called “beer preservatives” examined by the author, consisted of a solution of sodium salicylate and borax, dissolved in glycerine. Salicylic acid is employed in order to prevent fermentation in beer, which is exposed to great variations in temperature. Its presence is detected by the following process, suggested by Röse,[78] which is equally applicable to wine:—The beer (or wine) is acidulated with sulphuric acid, and well shaken with its own volume of a mixture of equal parts of ether and petroleum naphtha. After standing at rest, the ethereal layer is removed by a pipette, and evaporated or distilled until reduced to a few c.c. A little water and a few drops of a dilute ferric chloride solution are then added, and the liquid filtered: in presence of salicylic acid, the filtrate will exhibit a violet colour. In the case of wines, where the presence of tannic acid might interfere with the salicylic acid reaction, the filtrate is re-acidulated, then diluted, and the treatment with the ether mixture and iron chloride repeated. The second residue will now show the violet coloration, even in wines rich in tannin, and containing but 0·2 milligramme of salicylic acid per litre. The tannin can also be removed by precipitation with gelatine, and the colour test for salicylic acid subsequently applied. Glycerine is likewise sometimes used as a preservative of beer, and is also added to render the liquor richer in appearance, by communicating a viscosity to the froth which causes it to adhere longer to the sides of the glass. It can be quantitatively estimated by evaporating 100 c.c. of the sample in a capsule at a temperature of 75°, until the carbonic acid has been expelled, then adding about 5 grammes of magnesium hydroxide, and thoroughly stirring the mixture until it forms a homogeneous, semifluid mass. The contents of the dish are allowed to cool, and are then well digested with 50 c.c. of absolute alcohol, and the fluid portion afterwards separated by decantation, the residual mass being again treated with 20 c.c. of absolute alcohol, and the alcoholic solution thus obtained added to the first. The malose, parapeptone, etc., present in the solution are now precipitated by adding (with constant stirring) 300 c.c. of anhydrous ether, after which the liquid is filtered, and the filtrate concentrated, at first by spontaneous evaporation, subsequently by heating over the water-bath, until it assumes the consistency of a syrup, when it is placed in an exsiccator which connects with an air-pump, where it is allowed to remain for twenty-four hours. The syrupy residue is then digested with 20 c.c. of absolute alcohol and filtered, the filtrate being collected in a tared capsule, which is again exposed to the heat of the water-bath, and allowed to remain in the exsiccator for twelve hours, after which it is weighed. The increase in weight gives approximately the amount of glycerine contained in the beer examined.[79]
It is certain that many of the poisonous substances which in former times have been detected in beer, such as strychnine, hyoscyamine, picric acid, and picrotoxine, are not used at present. It is much more probable that such bitters as gentian and quassia may be met with, especially at times when hops are dear. These latter far exceed hops in bitterness, and do not exert deleterious effects upon health. Willow bark, or its active principle, salicine, has also been employed. The detection of some of the most apocryphal substitutes for hops is effected, according to Wiltstein,[80] by the following method: One litre of the beer is concentrated over the water-bath to a syrupy liquor, which is introduced into a rather capacious tared cylinder and weighed. The gum, dextrine, and mineral salts are first separated by adding to the syrup five times its weight of 95 per cent. alcohol, with which it is thoroughly mixed, and allowed to digest for twenty-four hours. The clear, supernatant solution is now drawn off, and the residue treated with a fresh quantity of alcohol, which is afterwards united with the solution first obtained, the whole being then evaporated until the alcohol is expelled. A small portion of the residue is dissolved in a little water, and tested for picric acid, as described later on. The remainder is repeatedly shaken with about six times its weight of pure benzol, which is subsequently removed by decantation, the operation being then repeated with fresh benzol, the two solutions added and evaporated to dryness at a very moderate temperature. The residue thus obtained is divided into three portions, which are placed in small porcelain dishes and tested as follows:—
To one portion a little nitric acid (sp. gr. 1·330) is added; if a red coloration ensues, brucine is present; if a violet colour, colchicine. A second portion is treated with concentrated sulphuric acid; the production of a red colour indicates the presence of colocynthine. To a third portion, a few fragments of potassium dichromate and a little sulphuric acid are added; if a purple-violet coloration takes place, strychnine is present.
The portion of the syrup which has remained undissolved by benzol is first dried over the water-bath, and then agitated with pure amylic alcohol, by which treatment picrotoxine and aloes, if present, will go in solution, and impart a bitter taste to the liquid.
The solution can be examined as subsequently directed for picrotoxine; the presence of aloes is best recognised by the characteristic saffron-like odour possessed by this body. The syrup which remains after the successive treatments with benzol and amylic alcohol is next freed from any remaining traces of the latter compound by means of blotting-paper, and then thoroughly agitated with anhydrous ether, which is afterwards removed and allowed to spontaneously evaporate. If the residue now obtained exhibits a wormwood-like aroma, and gives a reddish yellow solution, which rapidly changes to a deep blue when treated with concentrated sulphuric acid, absinthine is present. The syrup insoluble in ether may still contain quassine, gentipicrine, and menyanthine, and the presence of any of these bodies is indicated if it possesses a bitter taste, since the bitter principle of hops would have been removed by the foregoing treatment with solvents. The syrup is dissolved in a little warm water, the solution filtered and divided into two portions. To one a concentrated ammoniacal solution of silver nitrate is added, and the mixture heated: if it remains clear, quassine is probably present; the formation of a metallic mirror points to the presence of either gentipicrine or menyanthine. A second portion of the aqueous solution is cautiously evaporated in a small porcelain capsule, and a few drops of strong sulphuric acid are added to the residue: if no change takes place in the cold, but upon applying heat a carmine-red coloration appears, gentipicrine is present; if a yellowish brown colour, which afterwards changes to a violet, is produced, the presence of menyanthine is probable.[81]
Picric acid can be detected by means of the following tests:—
1. Upon shaking pure beer with animal charcoal, it becomes decolorised, whereas beer containing picric acid retains a lemon-yellow colour after this treatment.
2. The bitter taste of normal beer is removed by treatment with a little plumbic diacetate and filtering, which is not the case with the flavour imparted by the use of picric acid.
3. Unbleached wool or pure flannel will acquire a decided yellow colour if boiled for a short time in beer adulterated with picric acid, and afterwards washed.