WINE-MAKING
“When wine is heated, there is first an escape of an inflammable vapor
that burns with a bluish flame. A person needs only to have seen once
this preparation of hot wine to recall that curious flame flickering
over the boiling liquid and darting up little blue tongues. Now, this
inflammable vapor comes from alcohol, a fluid substance that gives to
wine its peculiar properties and is hence sometimes called spirits of
wine. There are, then, in wine two distinct liquids, one easily
reducible to vapor and called alcohol, the other slower to vaporize and
recognizable as water. This does not mean that the wine has been
watered: the water in question is not there as the result of fraud; it
belongs naturally to the wine and comes from grapes just as alcohol
does. Wine is therefore a natural mixture of a small proportion of
alcohol with a great quantity of water. In our ordinary wines the
proportion of alcohol for each hundred quarts of liquid varies from
nine to fourteen quarts.
“Wine is made from the juice of grapes. This juice, as it is pressed
out of the sweet grapes, has none of the taste or smell peculiar to
wine, for it does not yet contain any alcohol; but it does have an
agreeably sweet taste, the same taste that makes grapes so desirable a
fruit for the table. This pleasant flavor is due to a sort of sugar
present in the grapes. Examine carefully a handful of raisins such as
you buy at the grocer’s: you will detect on their surface, certain tiny
white grains that crunch under the teeth and have a sweet savor. Those
grains are little particles of sugar that have collected on the outside
of the grapes during the process of drying. Grapes, then, must contain
sugar.
“Well now, this sugar is exactly what causes the formation of alcohol.
What is sugar in the fresh juice of grapes is alcohol in the same juice
after it has fermented and turned to wine. Let us consider briefly how
this change comes about.
“The vintage is first of all subjected to a process of treading by men
who trample on the grapes in large vats, after which the resulting
mixture of juice and skins is left to ‘work,’ as we say. Before long
this liquid mush begins to heat of its own accord, and presently there
sets in a sort of boiling which liberates big bubbles of gas as if
there were a fire underneath. This working process is called
fermentation, and its seat is in the sugar of the grape-juice. Little
by little the sugar decomposes, splits apart as we might say, into two
substances very different from each other and also very different from
the sugar whence they came. Of these two substances one is alcohol; the
other is a gas already known to us—carbonic acid, the same gas that
plants feed on and that animals give forth in breathing; the same,
finally, as that produced by burning coal. The alcohol remains in the
liquid, which thus gradually loses its original sweet taste and
acquires instead a vinous flavor. The gas, on the contrary, works its
way to the surface, agitating the mass with a sort of tumultuous
movement like that of boiling water, and is dissipated in the
atmosphere.
“Let us bear in mind that carbonic acid gas is as invisible as the air
itself, that it has no odor, no color, and finally that it kills
quickly if inhaled in any considerable quantity. That explains the
danger lurking in a wine-vat during fermentation, or even in a
wine-cellar that lacks sufficient ventilation to carry off the perilous
gas. No one should enter such places without holding before one a
lighted taper at the end of a long stick. While the taper continues to
burn in the usual manner, one can proceed without fear: there is no
carbonic acid gas present. But if the flame becomes dim, gets smaller
and smaller, and finally goes out altogether, one must beat a hasty
retreat, for the extinction of the taper is a sure sign of the presence
of carbonic acid gas, and further advance would mean exposing oneself
to imminent death.
“But to return to the subject of wine-making, we were saying that the
sugar which imparts its sweet taste to the must (that is, the
unfermented grape-juice) changes its nature and divides into two parts:
alcohol, which remains in the liquid and turns it to wine, and carbonic
acid gas, which is dissipated in the atmosphere. When this process is
finished the wine is drawn off, leaving behind the residuum of skins
and pips. The final product is thus composed of a large quantity of
water from the grapes themselves, a small quantity of alcohol from the
sugar which has undergone the chemical change just described, and,
finally, a coloring substance furnished by the dark grape-skins.
“White wine is made from white grapes, which have skins with no
coloring matter; but it can very well be made from dark grapes, colored
though they are. The secret consists simply in this: the crushed grapes
are pressed before fermentation begins. In this way the juice is
separated from the skins, and, these latter being removed, the wine
will be white even with dark grapes. In short, the coloring matter in
grapes which gives its hue to red wine is contained solely in the
skins; and furthermore it is insoluble in water, but easily soluble in
alcohol. Hence it is only after fermentation has made some progress
that the liquid becomes colored by the dissolving of the coloring
matter through the agency of the alcohol that has been generated.
Accordingly, if the skins are removed before the juice ferments and
generates alcohol, the wine remains white, since it no longer contains
any coloring matter to dissolve.
“Some wines force out the corks from their bottles and are covered with
foam on being poured into glasses. These are foamy wines, and to
produce them the bottling must be done before fermentation is finished.
The carbonic acid gas then continues to form, but as it finds no way of
escape since the bottle is tightly corked, it dissolves in the liquid
and accumulates there, though all the while endeavoring to free itself;
and that is what makes the cork pop with a sharp report when the string
that holds it down is cut; that is what causes the wine to rush foaming
out of the bottle; and, finally, that is what gives the bead to a glass
of wine and makes a slight crackling sound as the bubbles burst on the
surface.
“Foamy wine has a pungent but agreeable taste owing to the carbonic
acid it contains. We drink, dispersed through the liquid, the same gas
as would kill us if freely inhaled; but it has no terrors except when
thus inhaled. Mixed with our drinks, it imparts to them a slightly tart
flavor, harmless and even salubrious, since it aids digestion. There is
carbonic acid gas in nearly all water that we drink, and it is in fact
by reason of this gas that water is able to hold in solution the small
proportion of stony matter that contributes toward the formation of our
bones. It is to this gas, finally, that effervescent lemonade, cider,
beer, and Seltzer water owe their pungency and their foam.”