FERMENTED BEVERAGES.
614. Description.—Among fermented beverages are included those drinks, containing alcohol, prepared by fermenting the sugars or starches of fruits, cereals or other agricultural products. Wine and beer, in their various forms, and cider are the chief members of this class of bodies. Koumiss, although a fermented beverage, is not included in this classification, having been noticed under dairy products. The large number of artificial drinks, made by mixing alcohol with fruit and synthesized essences, is also excluded, although the methods of analysis which are used may be applied also to them.
Fermented beverages containing less than two per cent of alcohol are usually regarded as non-intoxicating drinks. Beers are of several varieties, and the term includes lager beer, ale, porter and stout. Distilled liquors are obtained by separating the alcohols and other volatile matters from the products of fermentation by distillation. It is not practicable here to attempt a description of the methods of preparing fermented drinks. Special works on this branch of the subject are easy of access.[631]
615. Important Constituents.—Alcohol is the most important constituent of fermented beverages. The solid matters, commonly called extract, which are obtained on evaporation are composed of dextrins, sugars, organic acids, nitrogenous bodies and mineral matters affording ash on combustion. Of these the dextrins and sugars form the chief part and the proteid bodies nearly ten per cent in the case of beers made of malt and hops. In beers the bitter principles derived from hops, while not important by reason of quantity, are of the utmost consequence from a gustatory and hygienic point of view. The ash of fermented beverages varies with their nature, or with the character of the water used in making the mash. In the manufacture of beer, water containing a considerable proportion of gypsum is often used, and this substance is sometimes added in the course of manufacture, especially of wine. The presence of common salt in the ash in any notable quantity is evidence of the addition of this condiment, either to improve the taste of the beverage or to increase the thirst of the drinker. In cider the organic acids, especially malic, are of importance.
Glycerol is a product of fermentation and of the hydrolysis of the fats and oils in the substances fermented.
616. Specific Gravity.—In order to secure uniformity of expression, the specific gravity of fermented beverages is determined at about 15°.6, although that is a temperature much below the average found in American laboratories. The specific gravity may be determined by an alcoholometer, pyknometer or hydrostatic balance in harmony with the directions given in paragraphs [48-54] and [285]. By reason of the extractive matters held in solution, fermented beverages are usually heavier than water, even if the content of alcohol be twenty per cent or more. On the other hand distilled liquors are lighter than water.
617. Determination of Alcohol.—The determination of the percentage of alcohol present in a solution is based on two general principles. On the one hand, and this is the base of the methods in common use, the alcohol is secured mixed only with water and its amount determined by ascertaining the specific gravity of the mixture. On the other hand the quantity of alcohol in a mixture may be determined by ascertaining the temperature of the vapors produced on boiling. This is the principle involved in the use of the ebullioscope. The latter method is not employed to any extent in this country.
Use of the Alcoholometer.—The alcoholometer usually employed is known by the name of Gay-Lussac, who first made practical use of it in the determination of alcohol. It is constructed in such a way as to read directly the volume of absolute alcohol contained in one hundred volumes of the liquid at a temperature of 15°.6. The instruments employed should be carefully calibrated and thoroughly cleaned by washing with absolute alcohol before use. The stem of the instrument must be kept free from any greasy substance, and this is secured by washing it with ether. After this last washing the analyst should be careful not to touch the stem of the instrument with his fingers. It is most convenient to make the determination exactly at 15°.6, but when made at other temperatures the reading of the instrument is corrected by tables which may be found in works especially devoted to the analysis of wines.[632]
In this country the alcoholometer is used to some extent, but the official method is based upon the determination of the specific gravity by an instrument constructed in every respect like the alcoholometer, but giving the specific gravity of the liquor at 15°.6 instead of its percentage by volume in alcohol. The reading of the instrument having been determined at a temperature of 15°.6, the corresponding percentage of alcohol by volume or by weight is taken directly from the table given further on.
Fig. 123. Metal Distilling Apparatus.
Methods of Distillation.—The metal apparatus employed in the laboratory of the Department of Agriculture, for the distillation of fermented beverages in order to determine the percentage of alcohol by the method given above, is shown in the accompanying [figure]. The apparatus consists of a retort of copper carried on supports in such a way as to permit an alcohol or bunsen lamp to be placed under it. It is connected with a block tin condenser and the distillate is received in a tall graduated cylinder placed under the condenser in such a way as to prevent the loss of any alcohol in the form of vapor. Exactly 300 cubic centimeters of the wine or fermented beverage are used for the distillation. Any acid which the wine contains is first saturated with calcium carbonate before placing in the retort. Exactly 100 cubic centimeters of distillate are collected and the volume of the distillate is completed to 300 cubic centimeters by the addition of recently distilled water.[633] The cylinder containing the distillate is brought to a temperature of 15°.6, the alcoholometer inserted and its reading taken with the usual precautions.
Official Method.—The alcoholometers employed in the official methods are calibrated to agree with those used by the officers of the Bureau of Internal Revenue. They are most conveniently constructed, carrying the thermometer scale in the same stem with that showing the specific gravity. It is highly important that the analyst assure himself of the exact calibration of the instrument before using it. Inasmuch as the volume of the distillate may not be suited in all cases to the use of a large alcoholometer, it is customary in this laboratory to determine the specific gravity by means of the hydrostatic balance, as described further on. Attention is also called to the fact that, in the official method, directions are not given to neutralize the free acid of the fermented beverage before the distillation. Since the Internal Revenue Bureau is concerned chiefly with the determination of alcohol in distilled liquors, this omission is of little consequence. Even in ordinary fermented beverages the percentage of volatile acids, (acetic etc.,) is so small as to make the error due to the failure to neutralize it of but little consequence. In order, however, to avoid every possibility of error, it is recommended that in all instances the free acids of the sample be neutralized before distillation. In this laboratory, the distillations are conducted in a glass apparatus shown in the accompanying [figure]. The manipulation is as follow:[634]
Fig. 124. Distilling Apparatus.
One hundred cubic centimeters of the liquor are placed in a flask of from 250 to 300 cubic centimeters capacity, fifty cubic centimeters of water added, the flask attached to a vertical condenser by means of a bent bulb tube, 100 cubic centimeters distilled and the specific gravity of the distillate determined. The distillate is also weighed, or its weight calculated from the specific gravity. The corresponding percentage of alcohol by weight is obtained from the appended table, and this figure multiplied by the weight of the distillate, and the result divided by the weight of the sample, gives the per cent of alcohol by weight contained therein.
The percentage of alcohol by volume of the liquor is the same as that of the distillate, and is obtained directly from the appended table.
In distilled liquors about thirty grams are diluted to 150 cubic centimeters, 100 cubic centimeters distilled and the per cent of alcohol by weight determined as above.
The percentage of alcohol by volume in the distillate is obtained from the appended table. This figure divided by the number expressing the volume in cubic centimeters of the liquor taken for the determination (calculated from the specific gravity), and the result multiplied by 100 gives the per cent of alcohol by volume in the original liquor.
618. Determining the Specific Gravity of the Distillate.—The specific gravity of the distillate may be determined by the pyknometer, alcoholometer, hydrostatic balance or in any accurate way. The volume of the distillate is not always large enough to be conveniently used with an alcoholometer, especially the large ones employed by the Bureau of Internal Revenue. In the laboratory of the Agricultural Department, it is customary to determine the density of the distillate by the hydrostatic balance shown in paragraph [285]. The specific gravity is in each case determined at 15°.6, referred to water of the same temperature, or if at a different temperature calculated thereto.
619. Table for Use with Hydrostatic Plummet.—It is more convenient to determine the density of the alcoholic distillate at room temperature than to reduce it to the standard for which the plummet is graduated. In the case of a plummet which displaces exactly five grams, or multiple thereof, of distilled water at 15°.6, the corrections for temperatures between 12°.2 and 30° are found in the following table, prepared by Bigelow.[635]
If the weight of the alcoholic solution displaced be 4.96075 grams the apparent specific gravity 0.99215 and the temperature of observation 25°.4, the correction, which is additive, as given in the table is 0.00191 and the true specific gravity is 0.99406 and the percentage of alcohol by volume 4.08.
When the plummet does not exactly displace five grams of water at 15°.6, but nearly so, the table may still be used.
For example, suppose the weight of water displaced be 4.9868 instead of five grams. The apparent specific gravity of the water by this plummet is 0.99736 and the difference between this and the true specific gravity is 0.00264, which is a constant correction to be added to the specific gravity as determined in each case.
Correction Table for Specific Gravity.
Below 15°.6 Subtract; Above 15°.6 Add.
| Temp. | Correction. | Temp. | Correction. | Temp. | Correction. |
|---|---|---|---|---|---|
| 12.2 | 0.00047 | 18.2 | 0.00043 | 24.2 | 0.00163 |
| 12.4 | 0.00044 | 18.4 | 0.00046 | 24.4 | 0.00167 |
| 12.6 | 0.00042 | 18.6 | 0.00050 | 24.6 | 0.00172 |
| 12.8 | 0.00039 | 18.8 | 0.00053 | 24.8 | 0.00176 |
| 13.0 | 0.00037 | 19.0 | 0.00057 | 25.0 | 0.00181 |
| 13.2 | 0.00634 | 19.2 | 0.00061 | 25.2 | 0.00186 |
| 13.4 | 0.00032 | 19.4 | 0.00065 | 25.4 | 0.00191 |
| 13.6 | 0.00029 | 19.6 | 0.00068 | 25.6 | 0.00195 |
| 13.8 | 0.00027 | 19.8 | 0.00072 | 25.8 | 0.00200 |
| 14.0 | 0.00024 | 20.0 | 0.00076 | 26.0 | 0.00205 |
| 14.2 | 0.00021 | 20.2 | 0.00080 | 26.2 | 0.00210 |
| 14.4 | 0.00018 | 20.4 | 0.00084 | 26.4 | 0.00215 |
| 14.6 | 0.00015 | 20.6 | 0.00087 | 26.6 | 0.00220 |
| 14.8 | 0.00012 | 20.8 | 0.00091 | 26.8 | 0.00225 |
| 15.0 | 0.00009 | 21.0 | 0.00095 | 27.0 | 0.00230 |
| 15.2 | 0.00006 | 21.2 | 0.00099 | 27.2 | 0.00235 |
| 15.4 | 0.00003 | 21.4 | 0.00103 | 27.4 | 0.00240 |
| 15.6 | 0.00000 | 21.6 | 0.00107 | 27.6 | 0.00246 |
| 15.8 | 0.00003 | 21.8 | 0.00111 | 27.8 | 0.00251 |
| 16.0 | 0.00006 | 22.0 | 0.00115 | 28.0 | 0.00256 |
| 16.2 | 0.00009 | 22.2 | 0.00119 | 28.2 | 0.00261 |
| 16.4 | 0.00012 | 22.4 | 0.00123 | 28.4 | 0.00267 |
| 16.6 | 0.00016 | 22.6 | 0.00128 | 28.6 | 0.00272 |
| 16.8 | 0.00019 | 22.8 | 0.00132 | 28.8 | 0.00278 |
| 17.0 | 0.00022 | 23.0 | 0.00136 | 29.0 | 0.00283 |
| 17.2 | 0.00025 | 23.2 | 0.00140 | 29.2 | 0.00288 |
| 17.4 | 0.00029 | 23.4 | 0.00145 | 29.4 | 0.00294 |
| 17.6 | 0.00032 | 23.6 | 0.00149 | 29.6 | 0.00299 |
| 17.8 | 0.00036 | 23.8 | 0.00154 | 29.8 | 0.00306 |
| 18.0 | 0.00039 | 24.0 | 0.00158 | 30.0 | 0.00311 |
The table is only accurate when the distillate does not contain over seven nor less than three per cent of alcohol. If the distillate contain more than seven per cent of alcohol it is diluted and the compensating correction made.
620. Calculating Results.—The specific gravity of the alcoholic distillate having been determined by any approved method and corrected to a temperature of 15°.6, the corresponding per cents of alcohol by volume and by weight are found by consulting the following table.[636] If, for example, the corrected specific gravity be exactly that given in any figure of the table the corresponding per cents are directly read. If the specific gravity found fall between two numbers in the table the corresponding per cents are determined by interpolation.
Table Showing Percentage of Alcohol
by Weight and by Volume.
621. Determination of Percentage of Alcohol by Means Of Vapor Temperature.—The temperature of a mixture of alcohol and water vapors is less than that of water alone and the depression is inversely proportional to the quantity of alcohol present. This principle is utilized in the construction of the ebullioscope or ebulliometer. In this apparatus the temperature of pure boiling water vapor is determined by a preliminary experiment. This point must be frequently revised in order to correct it for variations in barometric pressure. The water is withdrawn from the boiler of the apparatus, the same volume of a wine or beer placed therein, and the vapor temperature again determined. By comparing the boiling point of the wine, with a scale calibrated for different percentages of alcohol, the quantity of spirit present is determined. When water vapor is at 100° a vin ordinaire having eight per cent of alcohol gives a vapor at 93°.8. The presence of extractive matters in the sample, which tend to raise its boiling point, is neglected in the calculation of results.
622. Improved Ebullioscope.—The principle mentioned in the above paragraph may be applied with a considerable degree of accuracy, by using the improved ebullioscope described below.[637]
The apparatus consists of a glass flask F, shaped somewhat like an erlenmeyer, closed at the top with a rubber stopper carrying a central aperture for the insertion of the delicate thermometer A B, and a lateral smaller aperture for connecting the interior of the flask with the condenser D. The return of the condensed vapors from D is effected through the tube entering the flask F in such a manner as to deliver the condensed liquid beneath the surface of the liquid in F as shown in the [figure]. The flask F contains pieces of scrap platinum or pumice stone to prevent bumping and secure an even ebullition. The flask F rests upon a disk of asbestos, perforated in such a way as to have the opening fully covered by the bottom of the flask. To protect F against the influence of air currents it is enclosed in the glass cylinder E resting on the asbestos disk below and closed with a detachable soft rubber cover at the top. The temperature between the cylinder E and the flask F is measured by the thermometer C and the flame of the lamp G should be so adjusted as to bring the temperature between the flask F and the cylinder E to about 90° at the time of reading the thermometer B. The bulb of the thermometer B may be protected by a thin glass tube carrying distilled water, so adjusted as to prevent the escape of the watery vapor into F. The thermometer B is such as is used for determining molecular weights by the cryoscopic method. It has a cistern at A which holds any excess of mercury not needed in adjusting the thermometer for any required temperature.
Fig. 125. Improved Ebullioscope.
A second apparatus, exactly similar to the one described, is conveniently used for measuring the changes in barometric pressure during the process of the analysis. The temperature of the vapor of boiling water having been first determined, the beer or wine is placed in F, and the temperature of the vapor of the boiling liquid determined after the temperature of the air layer between E and F reaches about 90°, measured on the thermometer C. By using alcoholic mixtures of known strength the depression for each changing per cent of alcohol is determined for each system of apparatus employed, and this having once been done, the percentage of alcohol in any unknown liquid is at once determined by inspecting the thermometer, the bulb of which is immersed in the vapor from the boiling liquid. In the apparatus [figured], a depression of 0°.8 is equivalent to one per cent of alcohol by volume. Full directions for the manipulation of the apparatus may be found in the paper cited above.
623. Total Fixed Matters.—The residue left on evaporating a fermented beverage to dryness is commonly known as extractive matter, or simply extract. It is composed chiefly of unfermented carbohydrates, organic acids, nitrogenous bodies, glycerol and mineral substances. Hydrochloric and sulfuric acids may also be found therein. If any non-volatile preservatives have been used in the sample, such as borax, salicylates and the like, these will also be found in the solid residue. The bodies which escape are water, alcohols, ethers and essential oils. The character of the residue left by wines and beers is evidently different. In each case it should contain typical components which aid in judging of the purity of the sample. For instance, in beers the substitution for malt of carbohydrate bodies comparatively free of proteids, produces a beer containing a deficiency of nitrogenous bodies. Pure malt beer will rarely have less than one-half of a per cent of proteids, while beer made largely of glucose, rice or hominy grits, will have a much smaller quantity. First will be described below the methods of determining the fixed residue left on evaporation, and thereafter the processes for ascertaining its leading components.
624. Methods of the Official Chemists.—Two methods are in use by the official chemists for determining the fixed solids in fermented beverages.[638] They are as follows:
Direct Method.—Fifty cubic centimeters of the sample are weighed, placed in a platinum dish about eighty millimeters in diameter and capable of holding about seventy-five cubic centimeters and evaporated on the steam bath to a sirupy consistence. The residue is heated for two and a half hours in a drying oven at the temperature of boiling water and weighed.
In Sweet Wines.—Ten cubic centimeters of the liquor are weighed and diluted to 100 with water. Fifty cubic centimeters of this solution are evaporated as described above.
Optional Method.—Fifty cubic centimeters of the sample are placed in a platinum or porcelain dish and evaporated on the steam bath until the volume is reduced to one-third. The dealcoholized liquid is washed into a fifty cubic centimeter flask, cooled and made up to the original volume. It is mixed thoroughly and the specific gravity ascertained with a pyknometer, hydrostatic balance or an accurately standardized hydrometer. The percentage of total solids is obtained from the appended table. The column on the left of the specific gravity gives the percentage of extract in a wine, as calculated by Hager, and that on the right the percentage of extract in a beer or wort, as calculated by Schultze. According to Baumert, however, Schultze’s table gives results which approximate more closely the data obtained by direct estimation than does Hager’s.
Tables of Hager and Schultze for
the Determination of Extract
by the Indirect Method.
| Hager. | Specific gravity. | Schultze. |
|---|---|---|
| 0.84 | 1.0038 | 1.00 |
| 0.86 | 1.0039 | 1.02 |
| 0.88 | 1.0040 | 1.05 |
| 0.90 | 1.0041 | 1.08 |
| 0.92 | 1.0042 | 1.10 |
| 0.94 | 1.0043 | 1.13 |
| 0.96 | 1.0044 | 1.15 |
| 0.98 | 1.0045 | 1.18 |
| 1.00 | 1.0046 | 1.21 |
| 1.02 | 1.0047 | 1.23 |
| 1.04 | 1.0048 | 1.26 |
| 1.06 | 1.0049 | 1.29 |
| 1.08 | 1.0050 | 1.31 |
| 1.10 | 1.0051 | 1.34 |
| 1.12 | 1.0052 | 1.36 |
| 1.15 | 1.0053 | 1.39 |
| 1.17 | 1.0054 | 1.41 |
| 1.19 | 1.0055 | 1.44 |
| 1.22 | 1.0056 | 1.46 |
| 1.25 | 1.0057 | 1.49 |
| 1.27 | 1.0058 | 1.51 |
| 1.30 | 1.0059 | 1.54 |
| 1.32 | 1.0060 | 1.56 |
| 1.34 | 1.0061 | 1.59 |
| 1.37 | 1.0062 | 1.62 |
| 1.39 | 1.0063 | 1.64 |
| 1.42 | 1.0064 | 1.67 |
| 1.44 | 1.0065 | 1.69 |
| 1.46 | 1.0066 | 1.72 |
| 1.48 | 1.0067 | 1.74 |
| 1.50 | 1.0068 | 1.77 |
| 1.52 | 1.0069 | 1.79 |
| 1.55 | 1.0070 | 1.82 |
| 1.57 | 1.0071 | 1.84 |
| 1.59 | 1.0072 | 1.87 |
| 1.61 | 1.0073 | 1.90 |
| 1.64 | 1.0074 | 1.92 |
| 1.66 | 1.0075 | 1.95 |
| 1.68 | 1.0076 | 1.97 |
| 1.70 | 1.0077 | 2.00 |
| 1.72 | 1.0078 | 2.02 |
| 1.75 | 1.0079 | 2.05 |
| 1.77 | 1.0080 | 2.07 |
| 1.79 | 1.0081 | 2.10 |
| 1.82 | 1.0082 | 2.12 |
| 1.84 | 1.0083 | 2.15 |
| 1.86 | 1.0084 | 2.17 |
| 1.88 | 1.0085 | 2.20 |
| 1.90 | 1.0086 | 2.23 |
| 1.92 | 1.0087 | 2.25 |
| 1.94 | 1.0088 | 2.28 |
| 1.96 | 1.0089 | 2.30 |
| 1.98 | 1.0090 | 2.33 |
| 2.00 | 1.0091 | 2.35 |
| 2.03 | 1.0092 | 2.38 |
| 2.05 | 1.0093 | 2.41 |
| 2.07 | 1.0094 | 2.43 |
| 2.09 | 1.0095 | 2.46 |
| 2.11 | 1.0096 | 2.48 |
| 2.14 | 1.0097 | 2.51 |
| 2.16 | 1.0098 | 2.53 |
| 2.18 | 1.0099 | 2.56 |
| 2.21 | 1.0100 | 2.58 |
| 2.23 | 1.0101 | 2.61 |
| 2.25 | 1.0102 | 2.64 |
| 2.27 | 1.0103 | 2.66 |
| 2.30 | 1.0104 | 2.69 |
| 2.32 | 1.0105 | 2.71 |
| 2.34 | 1.0106 | 2.74 |
| 2.36 | 1.0107 | 2.76 |
| 2.38 | 1.0108 | 2.79 |
| 2.40 | 1.0109 | 2.82 |
| 2.42 | 1.0110 | 2.84 |
| 2.44 | 1.0111 | 2.87 |
| 2.46 | 1.0112 | 2.89 |
| 2.48 | 1.0113 | 2.92 |
| 2.50 | 1.0114 | 2.94 |
| 2.52 | 1.0115 | 2.97 |
| 2.54 | 1.0116 | 2.99 |
| 2.57 | 1.0117 | 3.02 |
| 2.59 | 1.0118 | 3.05 |
| 2.61 | 1.0119 | 3.07 |
| 2.64 | 1.0120 | 3.10 |
| 2.66 | 1.0121 | 3.12 |
| 2.68 | 1.0122 | 3.15 |
| 2.70 | 1.0123 | 3.17 |
| 2.72 | 1.0124 | 3.20 |
| 2.75 | 1.0125 | 3.23 |
| 2.77 | 1.0126 | 3.25 |
| 2.79 | 1.0127 | 3.28 |
| 2.82 | 1.0128 | 3.30 |
| 2.84 | 1.0129 | 3.33 |
| 2.86 | 1.0130 | 3.35 |
| 2.88 | 1.0131 | 3.38 |
| 2.90 | 1.0132 | 3.41 |
| 2.92 | 1.0133 | 3.43 |
| 2.94 | 1.0134 | 3.46 |
| 2.96 | 1.0135 | 3.48 |
| 2.98 | 1.0136 | 3.51 |
| 3.00 | 1.0137 | 3.54 |
If it be desired to use this table for the examination of liquors containing a higher percentage of extract, Schultze’s table (intended originally for wort) may be consulted.
Gautier regards the fixed solids as the residue obtained on evaporating, in a flat platinum dish, ten cubic centimeters of wine at 100° for four hours and a half.[639]
The official French method is as follows: Twenty cubic centimeters of wine are placed in a flat bottom, platinum dish of such a diameter that the depth of the liquid therein does not exceed one millimeter. The dish should be immersed as totally as possible in the steam. The heating is continued for six hours.
The following method is used at the municipal laboratory of Paris:
Twenty-five cubic centimeters of wine are placed in a flat bottom, platinum dish seventy millimeters in diameter and twenty-five deep. The dish is placed on a water bath in such a manner that it just touches the surface of the water which is kept at a constant level. The heating is continued for seven hours.[640]
625. Determination in a Vacuum.—To avoid the changes and decomposition produced by heating, the fixed solids may also be determined by drying the sample in a vacuum over sulfuric acid. In this laboratory, it has been found that the process may be greatly facilitated by connecting the desiccating apparatus with the vacuum service of the working desks in which a vacuum corresponding to a mercurial column of 600 millimeters is obtained. The desiccator is provided with a valve whereby a minute current of dry air is allowed to flow through it. This current is not large enough to lessen the vacuum but is sufficient to greatly accelerate the rapidity of the evaporation. The evaporation is hastened also, in a marked degree, by absorbing the liquid with a piece of filter paper previously dried in a vacuum. When it is desired to examine the residue, however, it must be obtained in a flat dish exposing a large surface to evaporation.
626. Estimation of Water.—It is evident that the percentage of water in a fermented beverage is easily calculated when the percentage of alcohol by weight and that of the dry residue are known. In a given case, if the number of grams of alcohol in 100 of the sample be five and that of fixed solids four and a half, the quantity of water therein is 100 - (5.0 + 4.5) = 90.5 grams. In this case the volatile essences are counted as water, but these, at most, are so small in quantity as to be practically unweighable. Nevertheless, it must be admitted that direct drying, in many cases, may give erroneous results, especially when the sample contains an abundance of ethers and of glycerol. The loss which takes place on evaporation may be diminished by adding to the sample, before evaporation, a known weight of potassium sulfate in crystals, which serves to increase the surface of evaporation, to hasten the process and to obtain a quantity of residue in excess of that secured by direct evaporation in an open dish.
627. Total Acidity.—The acidity found in fermented beverages is due both to the natural acids of the materials from which they are made, and to those caused by fermentation. The typical acids also indicate the nature of the original materials, as malic in cider and tartaric in wine. The acids of beers are due almost exclusively to fermentation, and acetic is probably the dominant one. In determining total acidity, it is not always convenient to ascertain beforehand what acid predominates, nor to accurately distribute the acid among its various components. In the analytical work it is advisable, therefore, to estimate the total acid of cider as malic, of wines as tartaric and of beers as acetic. The process of titration is conducted as follows:
Expel any carbon dioxid that is present by continued shaking. Transfer ten cubic centimeters to a beaker and, in the case of white wines, add about ten drops of a neutral litmus solution. Add decinormal sodium hydroxid solution until the red color changes to violet. Then add the reagent, a few drops at a time, until a drop of the liquid, placed on delicate red litmus paper, shows an alkaline reaction.
One cubic centimeter of decinormal sodium hydroxid solution = 0.0075 gram tartaric, 0.0067 of malic and 0.006 gram of acetic acid.
628. Determination of Volatile Acids.—Fifty cubic centimeters of the sample, to which a little tannin has been added to prevent foaming, are distilled in a current of steam. The flask is heated until the liquid boils, when the lamp under it is turned down and the steam passed through until 200 cubic centimeters have been collected in the receiver. The distillate is titrated with decinormal sodium hydroxid solution and the result expressed as acetic acid.
One cubic centimeter of decinormal sodium hydroxid solution = 0.0060 gram acetic acid.
The acidity due to volatile acids may be determined by ascertaining the total acidity as above described, evaporating 100 cubic centimeters to one-third of their volume, restoring the original volume with water and again titrating. The difference between the first and second titrations represents the volatile acidity.
A method of determining volatile acidity in wines, without the application of heat, has been proposed by de la Source.[641] The sample, five cubic centimeters, freed of carbon dioxid by shaking, is placed in a flat dish about eight centimeters in diameter. In a separate portion of the sample, the total acidity is determined in the presence of phenolphthalien by a set solution of barium hydroxid, one cubic centimeter of which is equal to four milligrams of sulfuric acid. The sample in the flat dish is placed in a desiccator, which contains both sulfuric acid and solid potassium hydroxid, and left for two days, by which time it is practically dry. The residue is dissolved in two cubic centimeters of warm water and the dish is kept in the desiccator for an additional two days. By this time the volatile acids, even acetic, will have disappeared and the residual acidity is determined after solution in water.
The method is also applicable when wines have been treated with an alkali. In this case two samples of five cubic centimeters each are acidified with two cubic centimeters of a solution of tartaric acid containing twenty-five grams per liter. This treatment sets free the volatile acids, and their quantity is determined as before.
629. Titration with Phenolphthalien.—The total acidity is also easily determined by titration with a set alkali, using phenolphthalien as indicator. Colored liquors must be treated with animal black before the analysis. The sample is shaken to expel carbon dioxid and five cubic centimeters added to 100 of water containing phenolphthalien. The set alkali (tenth normal soda) is added until the red color is discharged. Even wines having a considerable degree of color may be titrated in this way.[642] The acidity, expressed as tartaric, may be stated as due to sulfuric by dividing by 1.53.
630. Determination of Tartaric Acid.—The determination of potassium bitartrate is necessary when an estimation of the free tartaric acid is desired.[643]
Fifty cubic centimeters of wine are placed in a porcelain dish and evaporated to a sirupy consistence, a little quartz sand being added to render subsequent extraction easier. After cooling, seventy cubic centimeters of ninety-six per cent alcohol are added with constant stirring. After standing for twelve hours, at as low a temperature as practicable, the solution is filtered and the precipitate washed with alcohol until the filtrate is no longer acid. The alcoholic filtrate is preserved for the estimation of the tartaric acid. The filter and precipitate are returned to the porcelain dish and repeatedly treated with hot water, each extraction being filtered into a flask or beaker until the washings are neutral. The combined aqueous filtrates and washings are titrated with decinormal sodium hydroxid solution.
One cubic centimeter of decinormal sodium hydroxid solution = 0.0188 gram potassium bitartrate.
The alcoholic filtrate is made up to a definite volume with water and divided into two equal portions. One portion is exactly neutralized with decinormal sodium hydroxid solution, the other portion added, the alcohol evaporated, the residue washed into a porcelain dish and treated as above.
One cubic centimeter decinormal sodium hydroxid solution = 0.0075 gram tartaric acid.
As, however, only half of the free tartaric acid is determined by this method:
One cubic centimeter decinormal sodium hydroxid = 0.0150 gram of tartaric acid.
631. Modified Berthelot-Fleury Method.—Ten cubic centimeters of wine are neutralized with potassium hydroxid solution and mixed in a graduated cylinder with forty cubic centimeters of the same sample. To one-fifth of the volume, corresponding to ten cubic centimeters of wine, fifty cubic centimeters of a mixture of equal parts of alcohol and ether are added and allowed to stand twenty-four hours. The precipitated potassium bitartrate is separated by filtration, dissolved in water and titrated. The excess of potassium bitartrate over the amount of that constituent present in the wine corresponds to the free tartaric acid.[644]
632. Determination of Tartaric, Malic and Succinic Acids.—Two hundred cubic centimeters of wine are evaporated to one-half, cooled and lead subacetate solution added until the reaction is alkaline.[645] The precipitate is separated by filtration and washed with cold water until the filtrate shows only a slight reaction for lead. The precipitate is washed from the filter into a beaker, by means of hot water, and treated hot with hydrogen sulfid until all the lead is converted into sulfid. It is then filtered hot and the lead sulfid washed with hot water until the washings are no longer acid. The filtrate and washings are evaporated to fifty cubic centimeters and accurately neutralized with potassium hydroxid. An excess of a saturated solution of calcium acetate is added and the liquid allowed to stand from four to six hours with frequent stirring. It is then filtered and the precipitate washed until the filtrate amounts to exactly 100 cubic centimeters. The precipitate of calcium tartrate is converted into calcium oxid by igniting in a platinum crucible. After cooling, from ten to fifteen cubic centimeters of normal hydrochloric acid are added, the solution washed into a beaker and accurately titrated with normal potassium hydroxid solution. Every cubic centimeter of normal acid saturated by the calcium oxid is equivalent to 0.0750 gram tartaric acid. To the amount so obtained, 0.0286 gram must be added, representing the tartaric acid held in solution in the filtrate as calcium tartrate. The sum represents the total tartaric acid in the wine.
The filtrate from the calcium tartrate is evaporated to about twenty-five cubic centimeters, cooled and mixed with three times its volume of ninety-six per cent alcohol. After standing several hours, the precipitate is collected on a weighed filter, dried at 100° and weighed. It represents the calcium salts of malic, succinic and sulfuric acids and of the tartaric acid which remained in solution. This precipitate is dissolved in a minimum quantity of hydrochloric acid, filtered and the filter washed with hot water. Potassium carbonate solution is added to the hot filtrate, and the precipitated calcium carbonate separated by filtration and washed. The filtrate contains the potassium salts of the above named acids. It is neutralized with acetic acid, evaporated to a small volume and precipitated hot with barium chlorid. The precipitate of barium succinate and sulfate is separated by filtration, washed with hot water and treated on the filter with dilute hydrochloric acid. The barium sulfate remaining is washed, dried, ignited and weighed. In the filtrate, which contains the barium succinate, the barium is precipitated hot with sulfuric acid, washed, dried, ignited and weighed. Two hundred and twenty-three parts of barium sulfate equal 118 parts of succinic acid. The succinic and sulfuric acids, as well as the tartaric acid remaining in solution, which is equal to 0.0286 gram, are to be calculated as calcium salts and the result deducted from the total weight of the calcium precipitate. The remainder is the calcium malate, of which 172 parts equal 134 parts malic acid.
According to Macagno, succinic acid may be estimated in wines by the following process:[646] One liter of the wine is digested with lead hydroxid, evaporated on the water bath and the residue extracted with strong alcohol. The residual salts of lead are boiled with a ten per cent solution of ammonium nitrate, which dissolves the salts of succinic acid. The solution is filtered, the lead removed by hydrogen sulfid, boiled, neutralized with ammonia and treated with ferric chlorid as long as a precipitate is formed. The ferric succinate is separated by filtration, washed and ignited. The succinic acid is calculated from the weight of ferric oxid obtained.
Malic acid in wines and ciders is determined by the method of Berthelot in the following manner:[647] The sample is evaporated until reduced to a tenth of its volume. To the residue an equal volume of ninety per cent alcohol is added and the mixture set aside for some time. The tartaric acid and tartrates separate, together with the greater part of the salts of lime which may be present.
The supernatant liquid is decanted and a small quantity of lime added to it until in slight excess of that required to neutralize the acidity. Calcium malate is separated mixed with lime. The solid matters are separated by filtration, dissolved in a ten per cent solution of nitric acid, from which the lime bimalate will separate in a crystalline form. The weight of calcium bimalate multiplied by 0.59 gives that of the malic acid.
633. Polarizing Bodies in Fermented Beverages.—The study of the nature of the carbohydrates, which constitute an important part of the solid matters dissolved in fermented beverages, is of the greatest importance. These bodies consist of grape sugars, sucrose, tartaric acid and the unfermented hydrolytic products derived from starch. A natural grape sugar (chiefly dextrose) is found in wines. Sucrose is also a very important constituent of sweet wines. The hydrolytic products of starch are found in beers, either as a residue from the fermentation of malt or from the rice, glucose, hominy grits etc., added in brewing. The character and quantities of these residues can be determined by the methods already given in the parts of this volume relating to sugars and starches. For convenience, however, and for special application to the investigation of fermented beverages a résumé of the methods adopted by the official chemists follows:[648]
634. Determination of Reducing Sugars.—The reducing sugars are estimated as dextrose, and may be determined by any of the methods given for the estimation thereof ([113-140]).
635. Polarization.—All results are to be stated as the polarization of the undiluted sample. The triple field shadow saccharimeter is recommended, and the results are expressed in the terms of the sugar scale of this instrument. If any other instrument be used, or if it be desirable to convert to angular rotation, the following factors may be employed:
| 1° Schmidt and Haensch | = 0°.3468 | angular rotation D. |
| 1° angular rotation D | = 2°.8835 | Schmidt and Haensch. |
| 1° Schmidt and Haensch | = 2°.6048 | Wild (sugar scale). |
| 1° Wild (sugar scale) | = 0°.3840 | Schmidt and Haensch. |
| 1° Wild (sugar scale) | = 0°.1331 | angular rotation D. |
| 1° angular rotation D | = 0°.7511 | Wild (sugar scale). |
| 1° Laurent (sugar scale) | = 0°.2167 | angular rotation D. |
| 1° angular rotation D | = 4°.6154 | Laurent (sugar scale). |
In the above table D represents the angular rotation produced with yellow monochromatic light.
(a) In White Wines or Beers.—Sixty cubic centimeters of wine are decolorized with three cubic centimeters of lead subacetate solution and filtered. Thirty cubic centimeters of the filtrate are treated with one and five-tenths cubic centimeters of a saturated solution of sodium carbonate, filtered and polarized. This gives a solution of nearly ten to eleven, which must be considered in the calculation, and the polariscope reading must accordingly be increased one-tenth.
(b) In Red Wines.—Sixty cubic centimeters of wine are decolorized with six cubic centimeters of lead subacetate solution and filtered. To thirty cubic centimeters of the filtrate, three cubic centimeters of a saturated solution of sodium carbonate are added, filtered and the filtrate polarized. The dilution in this case is nearly five to six, and the polariscope reading must accordingly be increased one-fifth.
(c) In Sweet Wines. (1) Before Inversion.—One hundred cubic centimeters are decolorized with two cubic centimeters of lead subacetate solution and filtered after the addition of eight cubic centimeters of water. One-half cubic centimeter of a saturated solution of sodium carbonate and four and five-tenths cubic centimeters of water are added to fifty-five cubic centimeters of the filtrate, the liquids mixed, filtered and polarized. The polariscope reading is multiplied by 1.2.
(2) After Inversion.—Thirty-three cubic centimeters of the filtrate from the lead subacetate in (1) are placed in a flask with three cubic centimeters of strong hydrochloric acid. After mixing well, the flask is placed in water and heated until a thermometer, placed in the flask with the bulb as near the center of the liquid as possible, marks 68°, consuming about fifteen minutes in the heating. It is then removed, cooled quickly to room temperature, filtered and polarized, the temperature being noted. The polariscope reading is multiplied by 1.2. Because of the action of lead subacetate on invert sugar ([87]) it is advisable to decolorize the samples with other reagents ([87-89]).
(3) After Fermentation.—Fifty cubic centimeters of wine, which have been dealcoholized by evaporation and made up to the original volume with water, are mixed, in a small flask, with well washed beer yeast and kept at 30° until fermentation has ceased, which requires from two to three days. The liquid is washed into a 100 cubic centimeter flask, a few drops of a solution of acid mercuric nitrate and then lead subacetate solution, followed by sodium carbonate, added. The flask is filled to the mark with water, shaken, the solution filtered and polarized and the reading multiplied by two.
636. Application of Analytical Methods.—(1) There is no rotation.—This may be due to the absence of any rotatory body, to the simultaneous presence of the dextrorotatory nonfermentable constituents of commercial dextrose and levorotatory sugar, or to the simultaneous presence of dextrorotatory cane sugar and levorotatory invert sugar.
(a) The Wine is Inverted.—A levorotation shows that the sample contains cane sugar.
(b) The Wine is Fermented.—A dextrorotation shows that both levorotatory sugar and the unfermentable constituents of commercial dextrose are present.
If no change take place in either (a) or (b) in the rotation, it proves the absence of unfermented cane sugar, the unfermentable constituents of commercial dextrose and of levorotatory sugar.
(2) There is right rotation.—This may be caused by unfermented cane sugar, the unfermentable constituents of commercial dextrose or both.
(a) The sugar is inverted:
(a₁) It rotates to the left after inversion.—Unfermented cane sugar is present.
(a₂) It rotates more than 2°.3 to the right.—The unfermentable constituents of commercial dextrose are present.
(a₃) It rotates less than 2°.3 and more than 0°.9 to the right.—It is in this case treated as follows:
Two hundred and ten cubic centimeters of the sample are evaporated to a thin sirup with a few drops of a twenty per cent solution of potassium acetate. To the residue 200 cubic centimeters of ninety per cent alcohol are added with constant stirring. The alcoholic solution is filtered into a flask and the alcohol removed by distillation until about five cubic centimeters remain. The residue is mixed with washed bone-black, filtered into a graduated cylinder and washed until the filtrate amounts to thirty cubic centimeters. When the filtrate shows a dextrorotation of more than 1°.5, it indicates the presence of unfermentable constituents of commercial dextrose.
(3) There is left rotation.—The sample contains unfermented levorotatory sugar, derived either from the must or mash or from the inversion of added cane sugar. It may, however, also contain unfermented cane sugar and the unfermentable constituents of commercial dextrose.
(a) The wine sugars are fermented according to directions in [262].
(a₁) It polarizes 3° after fermentation.—It contains only levorotatory sugar.
(a₂) It rotates to the right.— It contains both levorotatory sugar and the unfermentable constituents of commercial dextrose.
(b₁) The sucrose is inverted according to (c), in (2).
(b₂) It is more strongly levorotatory after inversion. In contains both levorotatory sugar and unfermented cane sugar.
637. Estimation of Sucrose, Dextrose, Invert Sugar, Maltose and Dextrin.—The total and relative quantities of these carbohydrates are determined by the processes already described ([237-262]).
638. Determination of Glycerol.—(a) In Dry Wines and Beers.—One hundred cubic centimeters of wine are evaporated in a porcelain dish to about ten cubic centimeters, a little quartz sand and milk of lime added and the evaporation carried almost to dryness. The residue is mixed with fifty cubic centimeters of ninety per cent alcohol, using a glass pestle or spatula to break up any solid particles, heated to boiling on the water bath, allowed to settle and the liquid filtered into a small flask. The residue is repeatedly extracted in a similar manner, with small portions of boiling alcohol, until the filtrate in the flask amounts to about 150 cubic centimeters. A little quartz sand is added, the flask connected with a condenser and the alcohol slowly distilled until about ten cubic centimeters remain. The evaporation is continued on the water bath until the residue becomes sirupy. It is cooled and dissolved in ten cubic centimeters of absolute alcohol. The solution may be facilitated by gentle heating on the steam bath. Fifteen cubic centimeters of anhydrous ether are added, the flask stoppered and allowed to stand until the precipitate has collected on the sides and bottom of the flask. The clear liquid is decanted into a tared weighing bottle, the precipitate repeatedly washed with a few cubic centimeters of a mixture of one part of absolute alcohol and one and five-tenths parts anhydrous ether and the washings added to the solution. The ether-alcohol is evaporated on the steam bath, the residue dried one hour in a water oven, weighed, the amount of ash determined and its weight deducted from that of the weighed residue to get the quantity of glycerol.
(b) In Sweet Wines.—One hundred cubic centimeters of wine are evaporated on the steam bath to a sirupy consistence, a little quartz sand being added to render subsequent extraction easier. The residue is repeatedly treated with absolute alcohol until the united extracts amount to from 100 to 150 cubic centimeters. The solution is collected in a flask and for every part of alcohol one and five-tenths parts of ether are added, the liquid well shaken and allowed to stand until it becomes clear. The supernatant liquor is decanted into a beaker and the precipitate washed with a few cubic centimeters of a mixture of one part alcohol and one and five-tenths parts ether. The united liquids are distilled, the evaporation being finished on the water bath, the residue is dissolved in water, transferred to a porcelain dish and treated as under (a).
639. Determination of Coloring Matters in Wines.—The methods of detecting the more commonly occurring coloring matters in wines as practiced by the official chemists are given below.
(a) Cazeneuve Reaction.—Add two-tenths gram of precipitated mercuric oxid to ten cubic centimeters of wine, shake for one minute and filter.
Pure wines give filtrates which are colorless or light yellow, while the presence of a more or less red coloration indicates that an anilin color has been added to the wine.
(b) Method of Sostegni and Carpentieri.—Evaporate the alcohol from 200 cubic centimeters of wine. Add from two to four cubic centimeters of a ten per cent solution of hyrochloric acid, immerse therein some threads of fat-free wool and boil for five minutes. Remove the threads, wash them with cold water acidified with hydrochloric, then with hot water acidified with hydrochloric, then with pure water and dissolve the color in a boiling mixture of fifty cubic centimeters of water and two cubic centimeters of concentrated ammonia. Replace the threads by new ones, acidify with hydrochloric and boil again for five minutes. In the presence of anilin colors to the amount of two milligrams per liter, the threads are dyed as follows:
| Safranin | light rose-red. |
| Vinolin | rose-red to violet. |
| Bordeaux-red | rose-red to violet. |
| Ponceau-red | rose-red. |
| Tropæolin oo | straw yellow. |
| Tropæolin ooo | light orange. |
(c) Detection of Fuchsin and Orseille.—To twenty cubic centimeters of wine add ten cubic centimeters of lead acetate solution, heat slightly and mix by shaking. Filter into a test-tube, add two cubic centimeters of amyl alcohol and shake. If the amyl alcohol be colored red, separate it and divide it into two portions. To one add hydrochloric acid, to the other ammonia. When the color is due to fuchsin, the amyl alcohol will in both cases be decolorized; when due to orseille, the ammonia will change the color of the amyl alcohol to purple-violet.
640. Determination of Ash.—The residue from the direct extract determination is incinerated at as low a heat as possible. Repeated moistening, drying and heating to low redness is advisable to get rid of all organic substances. When a quantitive analysis of the ash is desired, large quantities of the sample are evaporated to dryness and the residue incinerated with the usual precautions.
641. Determination Of Potash.—(a) Kayser’s Method.—Dissolve seven-tenths gram pure sodium hydroxid and two grams of tartaric acid in 100 cubic centimeters of wine, add 150 cubic centimeters of ninety-two to ninety-four per cent alcohol and allow the liquid to stand twenty-four hours. The precipitated potassium bitartrate is collected on a small filter and washed with fifty per cent alcohol until the filtrate amounts to 260 cubic centimeters. The precipitate and filter are transferred to the beaker in which the precipitation was made, the precipitate dissolved in hot water, the volume made up to 200 cubic centimeters and fifty cubic centimeters thereof titrated with decinormal sodium hydroxid solution, adding 0.004 gram to the final result, representing the potash which remains in solution as bitartrate.
(b) Platinum Chlorid Method.—Evaporate 100 cubic centimeters of the wine to dryness, incinerate the residue and determine the potash as in ash analysis.[649]
642. Determination of Sulfurous Acid.—One hundred cubic centimeters of wine are distilled in a current of carbon dioxid, after the addition of phosphoric acid, until about fifty cubic centimeters have passed over. The distillate is collected in accurately set iodin solution. When the distillation is finished, the excess of iodin is determined with set sodium thiosulfate solution and the sulfurous acid calculated from the iodin used.
643. Detection of Salicylic Acid.—(a) Spica’s Method.—Acidify 100 cubic centimeters of the liquor with sulfuric and extract with sulfuric ether. Evaporate the extract to dryness, warm the residue carefully with one drop of concentrated nitric acid and add two or three drops of ammonia. The presence of salicylic acid in the liquor is indicated by the formation of a yellow color due to ammonium picrate and may be confirmed by dyeing therein a thread of fat-free wool.
(b) Bigelow’s Method.—Place 100 cubic centimeters of the wine in a separatory funnel, add five cubic centimeters of sulfuric acid (1-3) and extract with a sufficient quantity of a mixture of eight or nine parts of ether to one part of petroleum ether. Throw away the aqueous part of the extract, wash the ether once with water, then shake thoroughly with about fifty cubic centimeters of water, to which from six to eight drops of a one-half per cent solution of ferric chlorid have been added. Discard the aqueous solution, which contains the greater part of the tannin in combination with iron, wash again with water, transfer the ethereal solution to a porcelain dish and allow to evaporate spontaneously. Heat the dish on the steam bath, take up the residue with one or two cubic centimeters of water, filter into a test-tube and add one to two drops of one-half per cent solution of ferric chlorid. The presence of salicylic acid is indicated by the appearance of a violet-red coloration. In the case of red wines, a second extraction of the residue with ether mixture is sometimes necessary. This method cannot be used in the examination of beers and ales.
(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.