MUST.
Must is the name applied to the juice of the grape before fermentation.
=Composition.=—A good, average must, contains in 100 parts by weight,
the following ingredients, and in the proportions as indicated, by
weight, according to Dr. Guyot; but the amount of sugar would be
considered too small in California:
Pure water, 78
Grape sugar (glucose), 20
Free acids (tartaric, tannic, etc.), 00.25
Salts, or organic acids (bitartrate), 1.50
Mineral salts, 0.20
Nitrogenous, fermentive matter, }
Essential oils, } .05
Mucilaginous and starchy substances, }
These constituents vary, however, according to variety of grape,
degree of maturity, soil, climate, etc.; and some of them may rise in
amount to double the average quantity given, or may even, under some
circumstances, descend to the one-fourth of it. Although all these
ingredients doubtless have important effects upon the quality of the
wine produced by fermentation, the acid giving zest and freshness of
taste, and the other minor ingredients, smoothness or harshness, as
the case may be, yet the principal one that we have to deal with is
the sugar, and it is the only one that the practical wine maker will
give much attention to, although in those countries where the grape in
some seasons does not ripen, the amount of acid is an important element
to be taken into consideration in testing the specific gravity of the
must. (See _Composition of Wines_, for further details.)
=Grape Sugar=, or glucose, as it is known in chemical language, as
already remarked, is the most important element entering into the
composition of must, and upon its quantity depends directly the amount
of alcohol contained in the wine. The intelligent wine maker, then, who
wishes to know what will be the alcoholic strength of the wine produced
by the must which he is about to subject to the action of fermentation,
will test the must to ascertain what percentage of sugar it contains.
This is very easily done by the use of an instrument prepared for the
purpose.
[Illustration: _Fig. 1._ Hydrometer.]
=Must-Scale.=—A certain quantity of sugar being heavier than the same
volume of water—pure cane sugar weighing about one and six-tenths to
one of water—it follows that the more sugar there is added to a given
quantity of water the heavier it becomes, and the more it will bear up
anything floating on it; or, as it is generally stated, the less of the
liquid will be displaced by the floating body. On this principle, the
specific gravity of liquids, or their weight as compared with water, is
ascertained. The instrument employed is known by the general name of
areometer, but it is now more commonly called a hydrometer, and various
specific names are given to it according to the uses for which it is
intended. When constructed for testing the strength of sugar syrups it
is called a syrup-scale, saccharometer, _pèse-sirop_, etc., and those
especially for testing musts are called must-scales, _pèse-moût_, etc.
These latter are constructed on the theory that the liquid contains
only cane sugar and water—the difference in specific gravity between
cane sugar and grape sugar being disregarded—and that its density
depends on the quantity of sugar; and although the density of must is
somewhat affected by other solid matters than sugar contained in it,
yet these instruments, whether syrup-scales or must-scales proper,
will give results sufficiently accurate for the purposes of the wine
maker, a small allowance being made for the other solids, as hereafter
mentioned. There are three instruments which are the most generally
used in this country: Oechsle’s must-scale, Balling’s saccharometer or
syrup-scale, and Baumé’s syrup-scale, or _pèse-sirop_. The degrees of
Oechsle’s instrument indicate specific gravity in the manner mentioned
under Table I; Balling’s indicates percentages of sugar directly; and
Baumé’s degrees are arbitrary. (See Tables II and III.) There are
other instruments used in France—the gleuco-œnometer, reading upwards
for spirit and down for sugar on the same stem, corresponding in
degrees to Baumé’s—and the gleucometer, which indicates at once the
percentage of alcohol which the wine will contain after fermentation.
Baumé’s and Balling’s instruments are better suited for use in
California, where the musts often show a specific gravity higher than
is indicated by Oechsle’s scale, which frequently is graduated only
up to 80 deg., or 19.75 per cent. of sugar. They are all made on the
same general plan, and are usually constructed of glass. The instrument
consists of a tube about the size of a pipe-stem, terminating below
in a bulb or expansion, weighted at the bottom so that it will stand
upright and float when placed in a liquid. The scale is marked on the
stem, commencing at the top and numbering downward. The first mark is
zero, and shows how far the hydrometer sinks in pure water. (Fig. 1.)
As hydrometers are not always accurate, it is safer before using one
to have it tested by a chemist or a gauger, as but few others have the
necessary skill or the instruments requisite for that purpose. If,
however, an instrument which has been tested is accessible, another one
can be easily compared with that by ascertaining if both sink to the
same point in the same sugar solutions.
TESTING FOR SUGAR.
Any person, provided with one of the hydrometers mentioned, can easily
ascertain the percentage of sugar contained in any must with tolerable
accuracy, providing the grapes from which it is pressed are ripe; for
if they are green, and contain an undue amount of acid, the density
will be materially affected by that. There is no occasion, however, for
making wine from green grapes in this State.
[Illustration: _Fig. 2._ Hydrometer-Jar.]
In addition to the hydrometer, it is necessary to be provided with
a thermometer with which to ascertain the temperature of the must.
Besides the hydrometer and the thermometer, the only other article
necessary is a glass tube closed at the bottom and provided with a
foot, so that it will stand upright, called the hydrometer-jar. (Fig.
2.) This jar should have a diameter a little greater than that of the
bulb of the hydrometer, and must be of such a height that the latter
instrument will stand upright and float freely in it, when filled
with a liquid. In the absence of the hydrometer-jar, an empty fruit
jar, or a tall tin cup or can will answer its purpose. In performing
the operation, see that all the articles used are perfectly clean,
more particularly the hydrometer, for anything that would slightly
affect its weight would render the result of the test useless. Having
taken this precaution, press the juice from a small quantity of
grapes and strain it through a cloth, and pour sufficient into the
hydrometer-jar, that when the hydrometer is plunged into it, it will
just bring the level of the liquid to the upper edge of the vessel, or
to such a height that the figure on the stem can easily be read. Now
place the thermometer in the must and ascertain its temperature, for
the instruments are intended to be used at a certain degree of heat,
although three or four degrees variation either way will not materially
affect the result. Baumé’s instrument, as originally constructed,
was graduated for a temperature of 10° Reamur, which corresponds
with 54½° F.; but as constructed now-a-days, is generally graduated
for a temperature of 58° or 60° F.; and Balling’s and Oechsle’s for
a temperature of 63½° F. Some of Balling’s instruments sold in the
market are graduated for 62° F. If it is found that the temperature is
above or below the degree indicated, it may be lowered by cooling, or
raised by warming, till about the right temperature is reached. Then
the hydrometer, being clean, should be taken by the stem at the top
and gradually lowered into the must until it floats. Press it down
slightly with the finger and let it come to equilibrium, being careful
that there is not a drop of water on the stem above the surface of
the liquid, nor a bubble of air below. On looking at the stem where it
meets the surface, it will be seen that the liquid there curves upwards
around the instrument, and that the top of this curve marks one degree
higher than the general surface. If the reading is taken from the point
marked by the top of the curve (the figures reading downwards), add one
degree, or in other words, ascertain the mark on the stem corresponding
to the general surface of the liquid. If Balling’s scale is used,
the number at this mark shows the percentage of sugar which the must
contains; if Baumé’s is used, consult Table II or III, and opposite
this number will be found the corresponding per cent. of sugar. If
Oechsle’s scale is used, find from Table I or II the specific gravity
and the corresponding sugar per cent. Under Table I instructions will
be found for reading Oechsle’s scale. If Baumé’s instrument is used,
and a table is not at hand, multiply the observed figure by 1.8, and
the product will be nearly the per cent. of sugar.
=Correction for Temperature.=—It is known that a sugar solution or
a must expands as the temperature increases, and contracts as it
diminishes; and nice experiments have been performed to show the
amount of dilatation and contraction at different temperatures, and
the consequent variation in the specific gravity of the liquid, but
there is considerable difference in the results of the researches of
different authors, and it would seem that further experiments are
necessary; but a rule may be deduced which may be used instead of
changing the temperature of the must to make it correspond with that
for which the instrument is graduated, and although not strictly
correct, is sufficient for our purpose; and that is to add one-half per
cent. to the sugar per cent. indicated by the hydrometer for every 15°
F. above the standard temperature, and subtract ½ per cent. for every
15° below. For instance, if Baumé’s instrument shows 22½ per cent. of
sugar at 75° F., the actual strength is 23 per cent., and it would mark
that at 60°. If the same instrument shows 23½ per cent. at 45° F., the
real strength is 23 per cent. In using Balling’s scale graduated at
63½° F., the 15° in our example would make 78½° for the first supposed
case, and 48½° for the second.
In most cases the variation in temperature will be so little that it
may be disregarded; but if the test is made soon after the grapes have
been exposed to a hot sun, the must may show a temperature of 90° or
95° F., and it would indicate one per cent. less than its real sugar
strength. But the temperature would go below the freezing point of
water before the must would mark one per cent. too much.
As the must contains a small quantity of acids and extractive matter
which affect its density, some authors recommend that from one-tenth to
one-fifteenth of the figures indicating the density by Baumé should be
deducted, calling the remainder sugar, and this is about equivalent to
deducting one for every twelve per cent. of sugar. But if the grapes
are ripe and the must is strained, for all practical purposes all of
the solid matter may be called sugar, considering that we make a pretty
liberal allowance of sugar for one per cent. of alcohol. Fresh must
should always be taken for the purpose of testing for sugar, for as
alcohol is much lighter than water, if fermentation has commenced, it
will be impossible to ascertain the amount of sugar by means of the
hydrometer.
=Sugar and Alcohol.=—It will be shown in the chapter on fermentation
that, in actual practice, it takes about two per cent. of sugar,
as indicated by the hydrometer, to produce one per cent. by volume
of alcohol; therefore, divide the percentage of sugar contained in
the must, as shown by the hydrometer, by two, and the quotient is
approximately the per cent. of alcohol which will be contained in the
wine after complete fermentation.
=Alcohol in Wine.=—A good, saleable dry wine ought to contain from
eleven to twelve or thirteen per cent. of alcohol; and to produce such
a wine the must should indicate from 22 to 26 per cent. of sugar by
the hydrometer. A wine which is soon to be consumed at home does not
require that degree of strength necessary for shipment abroad and for
keeping, and may contain only ten per cent. of alcohol, and even less,
and be found a very palatable drink, and less “heady” than that of a
higher degree of spirit. And a wine may contain as much as 14 per cent.
of spirit, and be very acceptable to the wine merchant for mixing with
weaker wines.
A must which does not contain more than 24 per cent. of sugar per
hydrometer, if properly managed, will complete its fermentation, and if
it does not contain less than 22 per cent., will make a good, sound,
shipping wine, which will keep in almost any climate. Mr. Crabb, a
well known wine maker of Oakville, in this State, writes me that such
a must will ferment dry in six days, but that if it contains more
than 24 per cent. of sugar, fermentation is likely to be arrested by
the amount of alcohol, when it amounts to 12 per cent. This gentleman
is an intelligent viniculturist and a practical man, and it would be
safe to follow his advice. Mr. Arpad Haraszthy, who is noted in this
connection, in his lecture on fermentation before the convention of
wine growers, held at San Francisco in September, 1882, indicated 22
per cent. as a proper degree of sugar in the must; and it is reported
that the wine makers of Los Angeles county, in fixing the prices of
grapes in 1882, adopted 23 per cent. as the standard. Undoubtedly the
fermentation will be finished sooner, and will be less troublesome,
if the must contains sugar within the limits of 22 and 24 per cent.,
than if allowed to go beyond. (See _Maturity_.) If it should go to 26
per cent. and beyond, the chances are that the fermentation will be
incomplete, and that a portion of the sugar will remain in the wine,
which will cause it to ferment when exposed to changes of temperature;
it may become _milk sour_, and there will be danger of rapid
deterioration. From which it follows that, except for making sweet
wines, the grapes should be gathered before they develop much more
than 24 per cent. of sugar. Supposing, however, that picking commences
as soon as the must shows 22 per cent., sufficient force should be
employed to finish before it goes beyond the limit indicated. For the
writer has seen grapes gathered at the beginning of the season and made
into wine which showed 11 per cent. of alcohol, when the wine made from
grapes of the same vineyard, gathered too late, either on account of
lack of pickers or of fermenting tanks, contained 14.5 per cent., and
was still sweet.