(c) Girard’s Method.—Extract a portion of the acidified liquor with ether as in the preceding methods, evaporate the extract to dryness and exhaust the residue with petroleum ether. The residue from the petroleum ether extract is dissolved in water and treated with a few drops of a very dilute solution of ferric chlorid. The presence of salicylic acid is indicated by the appearance of a violet-red coloration.
644. Detection of Gum and Dextrin.—Four cubic centimeters of the sample are mixed with ten cubic centimeters of ninety-six per cent alcohol. When gum arabic or dextrin is present, a lumpy, thick and stringy precipitate is produced, whereas pure wine becomes at first opalescent and then gives a flocculent precipitate.
645. Determination of Nitrogen.—The best method of determining nitrogen in fermented beverages is the common one of moist combustion with sulfuric acid. The sample is placed in the kjeldahl digestion flask, which is attached to the vacuum service and placed in a steam bath until its contents are dry or nearly so. The process is then conducted in harmony with the well known methods. Where large quantities of the sample are to be employed, as in drinks containing but little nitrogen, the preliminary evaporation may be accomplished in an open dish, the contents of which are transferred to the digestion flask before any solid matter is deposited. The same procedure may be followed when the sample foams too much on heating.
646. Substitutes for Hops.—It is often claimed that cheap and deleterious bitters are used in brewing in order to save hops. While it is doubtless true that foreign bitters are sometimes employed, the experience of this laboratory goes to show that such an adulteration is not very prevalent in this country.[650] Possibly strychnin, picrotoxin, quassin, gentian and other bitter principles have sometimes been found in beer, but their use is no longer common. It is difficult to decide in every case whether or not foreign bitters have been added. A common process is to treat the sample with lead acetate, filter, remove the lead from the filtrate and detect any remaining bitters by the taste. All the hop bitters are removed by the above process. Any remaining bitter taste is due to other substances. For the methods of detecting the special bitter principles in hops and other substances, the work of Dragendorff may be consulted.[651]
647. Bouquet of Fermented and Distilled Liquors.—The bouquet of fermented and distilled liquors is due to the presence of volatile matters which may have three different origins. In the first place the materials from which these beverages are made contain essential oils and other odoriferous principles.[652] In the grape, for instance, the essential oils are found particularly in the skins. These essential principles may be secured by distilling the skins of grapes in a current of steam. This method of separation, however, cannot be regarded as strictly quantitive.
In the second place, the yeasts which produce the alcoholic fermentation are also capable of producing odoriferous products. These minute vegetations, resembling in their biological relations the mushrooms, grow in the soil and reach their maturity at about the time of the harvest of the grapes. Their spores are transmitted through the air, reach the expressed grape juice and produce the vinous fermentation. The particular odor due to any given yeast persists through many generations of culture showing that the body which produces the odor is the direct result of the vegetable activity of the yeast. A beer yeast, after many generations of culture, will still give a product which smells like beer, and in like manner a wine yeast will produce one which has the odor of wine. The quantity of odorant matter produced by this vegetable action is so minute as to escape detection in a quantitive or qualitive way by chemical means. These subtle perfumes arise moreover not only from the breaking up of the sugar molecule, but are also the direct results of molecular synthesis accomplished under the influence of the yeast itself.
In the third place, the fermented and distilled liquors contain odoriferous principles due to the chemical reactions which take place by the breaking up of the sugar and other molecules during the process of fermentation. The alcohols and acids produced have distinct odors by which they are often recognized. This is particularly true of ethylic, propylic, butylic, amylic and oenanthylic alcohols and acetic acid. These alcohols themselves also undergo oxidation, passing first into the state of aldehyds which, together with ethers, produce the peculiar aroma which is found in various fruits. The etherification noted above is of course preceded by the formation of acids corresponding to the various aldehyds present. The formation of these ethers takes place very slowly during aging, and it therefore requires three or four years for the proper ripening of wines or distilled liquors. By means of artificial heat, electricity and aeration, the oxidizing processes above noted may be hastened, but it is doubtful whether the products arising from this artificial treatment are as perfect as those which are formed in the natural processes.
AUTHORITIES CITED IN PART SEVENTH.
[535] Bulletin 46, Chemical Division U. S. Department of Agriculture, pp. 24-25.
[536] Bulletin 42, Arkansas Agricultural Experiment Station, pp. 81 et seq.