J. L. W. (John Louis William) Thudichum.

A treatise on the origin, nature, and varieties of wine; being a complete manual of viticulture and œnology online

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can be obtained by the breaking up under the influence of
oxidizing agents of hydro-carbons, such as lactose, or sugar of
milk. It is probable that all the hydro-carbons, grape-sugar^
cellulose, cane-sugar, gum, and starch, which differ from each
other very little in chemical composition, and can mostly be
transformed the one into the other, are thus produced by the



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32 CHEMICAL DEVELOPMENT, [chap.

combination of simple chemical compounds and the elimi-
nation of oxygen. This process of reduction, as it is che-
mically termed, in contradistinction to the process in animals,
which consists mainly in the addition of oxygen to complex
bodies, and their consequent breaking up into simple ones,
the process of oxidation, is effected by the vegetable cells,
particularly of the leaves, under the influence of the rays of
the sun ; and it is certain that the green colouring matter or
chlorophyll, and a yellow ingredient, luteine, have an im-
portant mediating share in these processes. These trans-
formations are most active during the time at which the sun's
rays have the highest chemical power, i.e, when it stands in the
meridian and its rays are most nearly vertical ; it is then that
the greatest amount of oxygen is exhaled by the leaves, and
the greatest amount of nutritive products elaborated within
their cells and vessels. The ammonia, in its turn, furnishes the
nitrogenized ingredients of the vine, as of plants in general.
We know less of the various stages of its metamorphosis and
combination in the vine than in other plants. But it is cer-
tain that its hydrogen is substituted variously, by methyl, for
example, and that it then occurs as tri-methylamine in wine.
It probably enters into combination with carbonaceous pro-
ducts in such a manner as to surrender its character as a
strong alkali ; the less complicated products may still retain
the characters of feeble alkalies (alkaloids), but the higher pro-
ducts, the albuminous bodies, are either neutral or feebly acid.
The presence of ammonia in the elementary juice of the vine,
the sap, has been proved by direct experiment.

When in this manner a plant has been formed from
a seed (or in any of the various ways to be described later),
it is not at once, and in the same year, able to reproduce fruit
and seed. Three entire seasons are mostly required for the
development of the roots and wood of the plant to such a size
as to enable it to produce a ripe fruit. During these various
stages the following chemical compounds are met with in the
various parts and juices of the plant : —

The Sap, — The first fluid which rises in the canes at the
beginning of the spring is called sap. It is effused from any



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I] THE SAP OF VINES. 33

cut surface which is made upon any part of the vine, and from
the terminal cut surfaces of canes it sometimes runs in drops
in quick succession, like tears from the ^yes of man. The
French and Germans therefore term it " tears," and the act of
its effusion the " weeping " of the vine. This fluid remains
clear on boiling, and does not pass into fermentation either by
itself or after sugar has been dis-
solved in it A litre of it evaporated
leaves about 2*5 grms. of residue.
This contains a little acid potassium
tartrate, and perhaps gum and solu-
ble starch ; altogether,, the organic
ingredients amount to about 1*9 grm.
The remaining 0*6 g^m. are Inorganic
and form an alkaline ash, containing
lime, potash, and a trace of phosphoric
add. When the sap is evaporated
after a few drops of hydrochloric acid
have been added to it, a colourless
deliquescent residue is obtained,
which, on addition of caustic lime,
immediately evolves ammonia. Pro-
bably it does not contain any albu-
minous matters. The sap therefore
is a very elementary material, con-
taining only matter necessary for the
formation of the first shoots.

The rising of the sap in the cane
takes place with an enormous force.
This was first measured by Stephen
Hales more than a century ago. He
fixed a bent glass tube to the cut-off

end of a vine-cane, and observed ^'V;^^T^^:^:^Zt:^
that the effused sap rose in the tube

to the height of 21 feet On filling the glass tube with
mercury he observed that this was pressed up to the height
of 22 inches. In April 1849 this experiment was repeated
by Mohr, upon the canes of a Chasselas or Gutedel. He

D



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34



CHEMICAL INGREDIENTS.



[chap.



at first fixed glass tubes to the ends of tlie canes, but could
not carry them sufficiently high up in the air to prevent the
sap from overflowing. He thereupon used the little apparatus
figured in the engraving (Fig. 8), a glass bottle containing
mercury and water, and closed with a cork, through which two
tubes passed. With one, bent at right angles, the bleeding
end of the vine-cane was connected by caoutchouc tubing.
The other admitted of the rising of the mercury to a height
of above 30 inches. The apparatus having been fixed on
April 16, 1849, at 9.30 A.M., the rise of the mercury in the
tube was observed to take place as follows : —



Time.
9*45 A.M.
lO'IO „

10*30 ,»
II
"•30 „

12

12*43 PM'



Height of Hg.
I inch.
3f8 inches.

7
7.V

rh

8,',



Time.


Height of ffg.


2'9 P.M. . .


. . II inches.


347 M . .


. . 12 ,.


7 M . .


■ . 13 M


9-45 M . .


. . 15 .»


On April 17,




815 A. M. . .


• •. '9Am



This was the maximum reached by the mercury, after
which it gradually sank again to a lower level.

T\i^ young slioots of the vine contain acid tartrate of potash
in much larger quantity than the sap. Cellulose and chloro-
phyll in constantly increasing quantity, and the mineral
constituents already mentioned, are deposited within their
structure, and that of the leaves. In the expressed juice of
entire branches there are found vegetable fibrin, which is
deposited spontaneously with the chlorophyll as a green
deposit ; vegetable albumeny which is precipitated by boiling ;
tannin, recognized by its astringent taste, its inky reaction
with iron salts, and its precipitate with solution of gelatine ;
acid tartrates of potash and lime, which can be obtained
by evaporation and crystallization ; starch, recognizable by
its assuming a blue colour with iodine ; gum, precipitated
by alcohol ; mineral salts. The part remaining insoluble
consists mainly of lignine or cellulose ; of this substance all
wood, old and young, is composed. In the cell-cavities of
the wood there is deposited in autumn a quantity of starch.
When such ripe wood is rasped and boiled with water, the



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I.] CHEMICAL INGREDIENTS. 35

starch is extracted and gives the blue coloration with iodine
solution. The tendrils contain malates and tartrates and
little tannitty and have a taste of unripe fruit The grapes
contain in their unripe state malates and tartrates, mainly
of potassium, which vary in proportion according to the
period of development. Before the appearance of any sugar
malates prevail; when the grapes become sugary tartrates
prevail, which in the fully ripe grapes maintain their
preponderance. The grapes then also contain fibrin, albu*
men, gum, pectin, tannin, and in largest quantity the
sugar peculiar to fruit; the tannin is not in solution in
the juice, but deposited in the husk and seed, and requires
maceration for its extraction. The husk of the blue and
black grapes contains the blue colouring matter also deposited
in the insoluble state along with the tannin, and extractable
only by alcohol and acid, or wine. The stalks contain starch
during summer, but lose it towards autumn, and when the
grapes are ripe they contain tannin and acid. The amount
of acid in the grapes increases during their growth, and
decreases again during ripening. When the juice from
grapes of various periods of growth simply is considered,
without reference to the number and weight of the berries,
it is observed to become steadily less and less acid, as shown
by the following experiments : —

Juice of Blue Tyrol (Black Hambro') Grapes,



On August 15, 1858, quite unripe


contained 31 per mille acid


On „ 30, 1858, unripe, green


315


On Sept. II, 1858, little coloured .


28


On Oct. 23, 1858, ripe . . .


'3


On Nov. 4, 1858, „ . . .


13



Juice of Blue Burgundy {Pineatl) Grapes,

On August 15, 1858, quite unripe contained 34*5 per mille acid.

On „ 30, 1858, „ . „ 34

On Sept. II, 1858, half green, half blue „ 17*5

On Oct. 15, 1858, ripe ... ,» 12

On „ 23, 1858, „ . . . ,.9

On Nov. 4, 1858, „ . . . ,t 9

D 2



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36 CHEMISTRY OF GRAPES, [chap.

Juice of White Chasselas {Royal Muscaditu) or GutedeL

On August 1$, 1858, quite unripe . contained 34 per mille add.
On „ 30, 1858, ripening . . ,,15

On Sept II, 1858, eatable, not quite ripe ,, 11*5 „
On Oct 15, 1858, quite ripe . . „ 6 „

On „ 23, 1858, „ . . „ 6 „

On Nov. 4, 1858, „ . . „ 7-5

In the foregoing analyses the acidity is expressed as free
tartaric acid, contained in 1,000 parts of juice. In the black
grapes the permillage of acidity did not diminish or undergo
any change in the time between October 23 and November 4,
while in the white Chasselas it experienced an increase during
that period. We shall have to consider the question of the
changes of the acidity of grapes during ripening more in
detail in the following pages.

The proportion of juice to murk has been found in various
grapes as follows : —

White Chasselas grapeSy stalks removed, gave by strong
pressure — ^juice 97 per cent. ; murk of husks and kernels
3 per cent.

Black Pineau grapes, stalks removed, gave — juice 948 per
cent. ; murk 5*2 per cent.

Black Pineau, pressed with stalks, as in the Champa^fne,
gave— juice 91*8 per cent. ; murk (including stalks) 9 percent.

Black Pineau, which had been allowed to ferment with
husks and stalks, as in the preparation of Burgundy wine,
and then pressed, gave—wine 696 per cent. ; murk 304
per cent.

In this latter case the proportion of the murk is increased
by the absorption of much wine, which cannot be removed
by pressure.

SPECIAL INVESTIGATION OF THE RELATION OF ACID AND
SUGAR IN GRAPES DURING RIPENING.

The percentage of free acid present in grape-juice
diminishes with the increasing ripeness of the grape, while
the percentage of sugar increases at the same time con-
siderably. From this it has frequently been inferred, that,
in the process of ripening, the acid is transformed into
sugan On closer consideration it will, however, appear



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I.] ACID AND SUGAR DURING RIPENING. 37

that such a conclusion cannot be safely drawn from the mere
fact of the diminished percentage of free acid, as the weight
of the fruit augments considerably during the progress of
growth, and thus the total amount of free acid present in the
ripe grape may be actually greater than in the unripe fruit,
and yet its proportion per cent be considerably diminished.
Moreover, the free acid is not by any means a measure of the
total amount of acid present, as there is always some acid
united to an alkali, and a greater proportion of alkali in the
ripe fruit would account for a diminution of the free acid,
even without any increase in the weight of the fruit We
have therefore instituted the following experiments.

The grapes to be experimented on were selected so as to
correspond, as far as possible, to average samples in the same
state of growth. The berries were then detached from the
stalks, as close as possible to the berry, and the weight of one
hundred of them carefully taken. They were then mashed
in a mortar, and the free acid and sugar estimated, either in
the total mash, or in the juice of the mash only. In some
cases the combined acid was determined, by estimating the
amount of carbonate of potash present in the ash of the
juice. The amount of tartaric acid was determined in some
cases. The following tables show, first, the amount of acid,
sugar, &c per cent ; and, secondly, the amounts as contained
in one hundred berries.

Riessling Grapes, from RatienthaL

First Sample, taken Sept. 13, 1866.
Weight of 100 berries, 107*60 gnns., consisting of —

Skins 1 1 *49 gnns.

Kernels 7*95 „

Juice 88"i6 „

107-60 „

loo parts of juice The juice of xoo berries
contained contained

Add, calculated as free T * . . 2*821 per cent. 2*482 grms.

Combined . . 0*050 ,, 0043 »»

2871 „ 2*525 „

Sugar 2*98 ,, 2*630 ,,

Ash 2*60 „ 0*229 »»

1 The symbol T stands for tartaric acid.

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38 ACID AND SUGAR [chap.

Second Sample, taken October 12, 1866.
Weight of loo berries, 138*5 grms., consisting of—

Skins *4*95 grms.

Kernels 874 ,,

Juice 114*81 „

13850 »,

xoo parts of juice The juice of loo berries
_ contained contained

Acid, calculated as free 1' . .1 '493 per cent. i '722 grms.

Combined . . . 0'220 „ 0*245 ,,

1 713 M 1-967 ,.

Sugar ...... 12-IO „ 13*80 „

Ash 0*225 „ 0*293 M

Third Sample, taken November 16, 1866.

Weight of 100 berries, 145*6 grms., consisting of—

Skins 14*20 grms.

Kernels 9*07 ,,

Juice 122*33 »»

145*60 „

xoo parts of juice The juice of «oo t>crrie9

_ conuined contained

Acid, calculated as free T . . i'333 per cent 1*651 grms.

Combined . . . 0*196 „ 0*236 „

1*529 „ 1*887 „

Sugar 16*20 „ 19*80 ,,

Ash 0*274 »» 0-335 »»

Therefore the free and combined acids, calculated as tartaric
acid, amount to —

In 100 parts of juice. In juice of loo berries.
First sample .... 2*871 per cent. 2*525 grms.

Second sample .... 1713 „ 1'967 ,»

Third sample .... 1*529 „ 1*887 „

Of these total acids, the real tartaric acid amounted to —

Ib 100 parts of juice. In juice of loo berries^
Hrst sample .... 0-175 per cent. 0*154 grms.

Second sample .... 0*141 „ 0*162 „

Third sample .... 0-136 „ o*i68 ,,

The next three samples of the Gutedel grape were taken
from a garden at Darmstadt on the 17th of September, 1864.



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I]



DURING RIPENING,



39



They were all taken on the same day, from the same wall,
and represented different stages of ripeness. The skins and
kernels were not extracted from the msish, which was analysed
entire. The combined acid was not determined.



First Sample, quite unripe.

Weight of lOO berries, 106*50 grms., containing—

In 100 parts.
Sugar .... None.

Free acid, calculated as T . 2 '362 per cent.

Second Sample, half ripe.

Weight of 100 berries, I36'25 grms., containing —

In 100 parts.
Sugar . . . 5 76 per cent

Free acid, calculated as T . i 582 ,,

Third Sample, nearly ripe.

Weight of 100 berries, 279*39 grms., containing —

In 100 parts.
Sugar . . . _ . 8*87 per cent.

Free add, calculated as T . 0*877 >»



In 100 berries.

None.
2*504 grms.



In 100 berries.
6*488 grms.
215s „



In 100 berries.
24*782 grms.

2450 »»



In this, as in the former case, there is a great decrease in the
percentage of free acid, but the amount of it present in 100
berries is almost the sahie in the three samples.

Two samples of Muscatel grape, taken from a garden
wall at Dirmstein, on the 4th of October, 1866 :—

First Sample, less ripe.

Weight of 100 berries, 203 grms., containing —

In 100 parts. In 100 berries.

Sugar . . . . io'5 percent. 21 '31 5 grms.

Free acid, calculated as T . 1*255 ,, 2*547 ,,

' Second Sample, somewhat more ripe.
Weight of 100 berries, 307 grms., containing —

In xoo parts. In 100 berries.

Sugar . . . . 15*40. percent. 47*278 grms.



Free acid, ca!culate<l as T



3100



In this last sample the amount of free acid in 100 berries
has actually increased perceptibly, although the percentage,
as in all the former samples, has diminished. If we t^ke
it for granted that, in the case of the Gutedel and Muscatel



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40 RIPENING OF ENFARIN£. [chap.

grapes, the amount of combined acid increases with the
increasing ripeness, then the total amount of acid present
in ICO berries would show a decided increase with the in-
creasing ripeness, instead of a diminution, as has been
assumed. While, in the case of the Riessling grape, we
have an increase of sugar from 2*63 grms. on 13th September,
to 13*8 grms. on 12th October; the total acid shows a
diminution from 2525 grms. to 1*967 grms. Then, on i6th
November, the sugar has risen to 198 grms., while the acid
has sunk only to 1*887 grms., thus having in fact almost
remained stationary.

The case of the Gutedel is even more striking, for there
we have an augmentation of sugar from 00 in the first
sample, to 24782 grms. in the third, the acid at the same
time sinking from 2504 to 2*450 grms. or only '054 grm.
= jnr part.

But although the foregoing analyses do not justify the
conclusion that in the process of ripening acid is converted
into sugar, such may possibly be the case. We have then to
assume that at a certain stage of growth the conversion of
acid into sugar begins, and keeps pace with the production
of acid in such a manner as to keep the amount of acid
present always the same, though the percentage diminishes
considerably. On the whole, we are led to the conclusion
that the acid, if it has anything to do with the production
of sugar, does so by an action similar to that which dilute
sulphuric acid exerts in the conversion of starch into sugar.
The acid suffers no change in the process, a small quantity
being capable of producing a large quantity of sugar.

We have thus shown that there is during ripening but
a slight, and frequently no diminution in the total amount
of acid present in an entire grape, and that the mere per-
centage of acid is not an indication of such amount.

PECULIARITY OF RIPENING OF THE GRAPES OF THE
"ENFARINJfe." ENGLISH "BLACK CLUSTER."

The "enfarin^" or befloured vine is a common vine in
the Jura, and more particularly peculiar to the vineyards



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I.] RIPENING OF ENFARINE. 41

of Arbois. It is one of the class of vines whose fruit con-
tains most acid and least sugar, and would therefore offer
few advantages for cultivation, were it not for the great
abundance of its fruit and the inestimable property of its
great resistance to the hardships of the mountain climate.
It is mostly mixed with the Poulsard, the Trousseau, and
the Baclaa. If its juice does not exceed ^ of the entire
mixture, it is said to be beneficial to the wine.* The acidity
of the grai>es of this vine does not always diminish with its
maturity, and the sugar does not always increase.

Experitnefiis made in 1863.^

On September 16 some of the very ripest grapes, as ripe
indeed as the vine can yield them, were selected.

They yielded in 1,000 parts of juice : total acid, calculated
as tartaric, 23*1 ; sugar, 153*9.

On September 19 three lots of grapes- were selected.

1. The ripest grapes chosen from amongst the blackest
gave must which yielded : acid, 248 ; sugar, 1 59-9.

2. Red grapes without any black appearance : acid, 23*4 ;
sugar, 1 50*0.

3. Grapes, partly red, partly black: acid, 23*4; sugar,
128-9.

Experiments made in 1864.

On September 27 three lots were again selected.

1. The most ripe black grapes : acid, 21-4 ; sugar, 1567.

2. Red grapes about to become black: acid, 2r8; sugar,

1351.

3. Green grapes just beginning to get pink: acid, 21 -8;
sugar, 1 35' I.

Vintage of September 28. — Four lots were cut.

1. The blackest grapes in the apparently highest state of
maturity gave : acid, 21-4; sugar, 1567.

2. Grapes of a violet-red colour, with no green : acid, 244 ;
sugar, 60-3.

* Rendu, Ampelographie fran9aise, p. 255.

* Pasteur, Maladies du Vin, p. 202 ; Vitography and Synonyms, see Babo,p. 158.



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42 RIPENING OF ENFARINE, [chap.

3. Reddish black and blackish red grapes: acid, 2r8;
sugar, 1464.

4. Quite green grapes, and grapes which began to get red :
acid, 25-5 ; sugar, 795.

Vintage of September 30. — Three lots of grapes were
selected.

1. Grapes with black surfaces : acid, 18*3; Sugar, 167*7.

2. Grapes black at the point, red at the insertion of the.
stalk: acid, 225 ; sugar, 1327.

3. Red violet grapes, without black : acid, 245 ; sugar, 102*3.

From the analyses of the vintages of September 19, 1863,
and September 27, 1864, it follows that the acidity of the
red grapes, and of those which are partly red and partly
black, is less than the acidity of the quite black grapes. At
a certain moment of maturation, if not during the whole process
of ripening, the amount of acid increases therefore, instead of
diminishing, as has hitherto been supposed to be the rule for
all fruit. Consequently the fact speaks against the assumption,
that the sugar is a product of transformation of the malic
and tartaric acid.

The vintages of September 28 and 30, 1864, do not give the
same result. Here the amount of acid decreases somewhat irt
a certain proportion with the increase of sugar. But they
show, with the first analyses, the curious fact that the quantjty
of acid changes very little, while that of the sugar increases
very much.

The second lot of the vintage of September 28, 1864 (red
grapes), contained less sugar than the fourth, which was made
up of less ripe, namely green, or reddish green grapes. Here
a diminution of sugar might be assumed as a result of
ripening, as before we have concluded upon an increase of
acid. The red grapes No. 2 of the vintage of September 19
had much more sugar than the red grapes No. 2 of Sep-
tember 30. They were a little more advanced, and from
another vineyard.

The ripe "enfarind" of 1863 was more acid and less sweet
than that of 1864.



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I,] RIPENING OF PLOUSSARD, 43

PROCESS OF RIPENING OF THE **PL0USSARD" GRAPES.

This vine is also called Poulsard^ and Poulsare, and is
largely cultivated in the Jura, on account of its strong
constitution and the abundance and excellence of its
grapes. Its red wine has great finesse and an agreeable
taste, but it sheds its colour rapidly, when in cask in two
or three years, and is very delicate and apt to pass into
acetous fermentation.

Experiments made in 1863.^

Vintage of September 7. — ^This was divided into three lots.
No. I being the ripest black grapes: acid, 8*5 ; sugar, 195*4.

2. Red grapes, termed " grains lie de vin : " acid, not de-
termined; sugar, 1357.

3. Green grapes just becoming red : acid, not determined ;
sugar, 955.

The character of the total must which the entire vintage
woyld yield can be judged from the fact that out of 13 '495
kilos, of these grapes 9433 gave must of composition i ; 3*862
gave must of composition 2, and 0200 gave must of composi-
tion 3.

A few very ripe grapes gave must containing : acid, 63 ;
sugar, 200*3.

Vintage of September 16. — i. The blackest grapes of the
ripest bunches gave : acid, 6*4 ; sugar, 209*4.

2. Half ripe grapes, or those between red and black : acid,
1 8*8 ; sugar, 165.

3. Red grains, called " grains lie de vin," showing neither
green nor black : acid, 18*7 ; sugar, 146*3.

4. Green grains beginning to show a rosy tint : acid, 206 ;
sugar, 84*9.

Vintage of September 18. — Ripest grapes of the blackest
bunches: acid, 64; sugar, 210*5.

* Rendu, p. 253. * Pasteur, p. 209.

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44 RIPENING OF PLOUSSARD. [chap.

Experiments made in 1864.

Vintage of September 27.— Blackest grapes of ripest bunches :
acid, 8*8 ; sugar, 2150.

Vintage of September 28. — Blackest grapes from ripest
bunches of the best situation, renowned for giving the best
wine of Arbois : acid, 83; sugar, 221*5.

In the vintage of September 16, 1863, it was omitted to
take a sample of merely ripe grapes, like those of No. i of
September 7. We may assume it to have contained 8 g^ms.
of acid and 200 grms. of sugar per litre.

Nos. 4, 3, and 2 of the vintage of September 16, 1863,
show that the process of ripening consisted at that period
mainly in this, that the green and red grapes took up sugar.
In the riper grapes, however, the process showed itself as a
diminution of acid. In passing from 4, green, to 3, red, the
grapes lost 2 grms. of acid, and gained more than 60 grms.
of sugar per litre of must. On the other hand, the red grapes,
during the process of getting partly black, lost only an insig-
nificant amount of acid while gaining nearly 20 grms. of
sugar. We see, further, that the grapes already partly black
or three-quarters ripe, in passing to perfect maturity, lose



Online LibraryJ. L. W. (John Louis William) ThudichumA treatise on the origin, nature, and varieties of wine; being a complete manual of viticulture and œnology → online text (page 5 of 64)