=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.
[Illustration: 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]
[Illustration: 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.