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Bulletin - Bureau of Chemistry

United States. Bureau of Chemistry



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Enologlcal Studies, No. 4. Iwued November 20, 1911 .


H. W. WILEY, Chief of Baraga.





Enological Chemist.




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U. S. Department of Agbicoltube,

Bureau of Chemistry,
Washington^ D. C, March 27, 1911.
Sm: I have the honor to submit for your approval a report on the
results of a three-year investigation of the composition of American
grapes, conducted at Charlottesville, Va., and Sandusky, Ohio, by
William B. Alwood, the enological chemist of this bureau, covering
the principal commercial varieties of American grapes grown in the
central and eastern sections of the country, and also other varieties
not generally cultivated. These data, even though the study is far
from complete, are of practical importance to the grape growers and
manufacturers of grape by-products, as well as of scientific interest,
and I recommend their publication as Bulletin No. 146 of the Bureau
of Chemistry.

Respectfully, H. W. Wiley,

Chief of Bureau.
Hon. James Wii^on,

Secretary of Agriculture.

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In the conduct of certain enological work it became evident that
there were ahnost no chemical data available regarding the character
of grapes grown in Virginia, in northern Ohio, in northern and
central New York, and in some other parts of the country. The
condition was much the same as that which was found in the begin-
ning of the enological studies on the production of cider. It is
evident that in order to treat a subject of this kind in a rational way
it is important that the character of the fruits under consideration
should be definitely known. After the investigation on the compo-
sition of the grapes in the Piedmont region of Virginia was begun it
was found advisable to establish a laboratory, or laboratories, for
further studies on the composition of this fruit and the products
made therefrom in the localities which have become so famous for
the production of grapes, grape juices, and wines. The establishment
of a branch of the enological investigations at Sandusky, Ohio,
rendered it possible to study in situ the character of the grapes pro-
duced in that region. This study has now continued over a period
of three years, and data are at hand for drawing at least preliminary
conclusions respecting the general character of the fruit produced.
As is the case in every grape-growing country, it has been found in
northern Ohio and central and northern New York that the character
of the grape varies from season to season, and often in the same vine-
yard or locality during a given season. This variation shows the
necessity which exists in this locality, as well as everywhere else, of
securing by careful selection the grapes which are to be used for
specific purposes. Those that are sound, healthy, mature, and suit-
able for the purpose should be separated from the imperfect, unripe,
damaged, or otherwise undesirable varieties. In the manufacture of
unfermented grape juice, for instance, it is desirable that the grapes
yield a juice which is palatable, wholesome, and easily treated. It
is not desirable to bottle the fresh juices and sterilize them without
removing, in so far as possible, the sedimentary matters which will
be deposited on heating and standing. Many varieties of grapes lend
themselves much more readily to treatment of this kind than others.
The chemical composition and physical properties of the fruit and its
amenability or resistance to treatment, either in the preservation of
the juice in an unfermented state or in the manufacture of wine, are



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of the greatest importance. As is well known, the predominant acid
in ripe grapes is tartaric. The presence of this acid, either in a free
state or in combination with lime or potash, is necessary to give to
the grapes the peculiar flavor for which they are noted. In other
words, the acid content of the grape is one of the ingredients of chief
importance from an organoleptic point of view. A grape which is
without acid would be totally insipid, and would yield a juice not
much better than sweetened water. On the other hand, a grape juice
in which the acid is excessive is impalatable, at least to most persons.
Hence the production of a grape with the proper degree of acidity to
give character and not enough to impair taste is of great importance.

The studies which have been made and which are detailed in the
following pages throw much light on this important problem, even
though they are far from complete, indicating what varieties of
grapes and what conditions of environment give the best results.

Equally important from the point of view of vinification is the
sugar content of the grape. The only source of natural alcohol in
wine is fermentation of the sugars which exist in the original grape.
These sugars exist in combination with other bodies, many of which
enter into the finished product and serve to give it character and
quality. In fact, the smaller the quantity of alcohol which can be
secured in the finished wine, and at the same time permit of its
manufacture and keeping, the better. Other things being equal, the
wine which has the smallest percentage of alcohol is to be preferred.
The data which have been secured indicate the varieties of grapes
which give the best percentage of sugar for proper fermentative

Tliese studies will lay broad and deep the foundation for the prac-
tical working out of the problem of the utilization of grapes for the
various purposes for which grape products are employed. While the
work has been carried on under the general direction and supervision
of the Chief of the Bureau of Chemistry, the details of it and the
technique of the processes have been in the hands of Mr. William B.
Alwood, who has given to the work his undivided attention and has
with enthusiasm and success attacked the many problems which
have been presented.

H. W. Wiley,

Chief of Bureau,

Washington, D. C, March 10, 1911.

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Ob jec t of the investigation 7

Grapes grown in Ohio and New York 8

Methods of obtaining Bamples 8

Preparation of the sample tor analysis 9

Tests and analyses made 10

Investigation of 1908 12

Investigation of 1909 13

Investigation of 1910 14

Seedlings and unknown varieties 17

Grapes grown in Virginia, 1908-1910 18

Tabulation of analytical data on samples collected at Sandusky, Ohio 20

Data for 1908 20

Data for 1909 21

Dato for 1910 27

Tabulation of analytical data on samples grown and analyzed at Charlottes-
ville, Va 35


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In the discharge of duties devolving upon the Bureau of Chem-
istiy under the food and drugs act it became apparent that definite
data on the methods of wine making and of the products made in the
several wine districts of the country were needed. As chemical data
on the composition of the fruit used in the manufacture of grape
juices and wines were not available, it was found necessary to make
a fairly complete fundamental study of the grape and the by-prod-
ucts made from this fruit. As a first step in this direction a detailed
study was made of the chemical composition and general character
of the several varieties of grapes grown in the Central and Eastern
States, especially those sent to the wineries at Sandusky, Ohio, with
a view to determining the suitability of these grapes for food purposes
and for wine production. Fiulher than this a chemical study of the
commercial wines produced in the middle and eastern wine-growing
districts was also found necessary for the purpose of comparing their
quality with that of wines which might be made under the direction
of the bureau from the grapes commonly used at the wineries for this

The need of this investigation in the administration of the food
law is readily seen if one compares the widely varying statements of
the grape growers and the wine makers as to the quality of the fruit
produced and the possibility of making straight wines from this fruit,
and also if one is familiar with the general practice of watering and
sugaring (i. e., gallizing) the wines made in the districts mentioned.
For these reasons it is important to determine fully the character of
the strictly nature wines made from these grapes. There appeared
to be no other method of seciuing these data than by a thorough
chemical investigation covering the whole subject of the fruit grown
and the character and composition of the wines produced and sold
in the districts in question. The term *' American grapes" is here
used to distinguish native seedlings and crosses of these with the


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European species produced in America, from the distinctly European
varieties grown so largely in California.

It is claimed by some that the grapes of New York State and the
Atlantic seaboard States are richer in sugar and not so acid as the
fruit grown in the Lake Erie district. Because of the proximity to
a very large grape-growing industry and of the important wine
industry located there the work has thus far been carried on chiefly at
Sandusky, Ohio, but it is intended to extend it as rapidly as possible
to other important centers. A large portion of the northern grape
belt- has already been covered in this preliminary investigation, and
the importance of the crop and its by-products and the necessity for
accurate information seem to fully justify this course. But the data
now in hand will render possible more detailed investigations of cer-
tain specific featiures — as, for instance, the variability in composition
of the more important varieties under differing conditions of soil,
climate, and culture — which appear to promise results of much prac-
tical importance.


In an investigation of this nature the character of the sample used
is of great importance. The data for the individual samples show
that the difference in composition between samples from the same
source may be sufficient to be confusing. Hence, with a view to
forestalling hasty conclusions, a very large number of samples, from
as many sources as possible, have been examined. This should ren-
der the averages presented quite reliable. There will certainly be a
very considerable variation in composition from year to year, the
extent of which can only be determined by continuing these examina-
tions until sufficient data have been secured to furnish a basis for a
final statement.

The season was so far advanced when this work was begun in 1908
that arrangements could not be made to secure samples from a large
number of individual growers; hence they were taken at the wine
cellars. But for the years 1909 and 1910 a large number of samples
were secured directly from the growers, and to check against the
results so obtained samples were taken from the wine cellars. In
getting samples from growers the selection of ''extra quality'' has
been prevented as far as possible, the aim being to use the average
commercial fruit. In any case the large number of samples exam-
ined from the various sources minimizes the incidental variations so
as to warrant a reasonable belief that the averages herein presented
represent the quality of the fruit for the season in question.

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The two elements of prime importance in the grapes used for the
manufacture of unfermented grape juice, for wine making, or for
other by-products, are the amount of sugar and the amount of acid
present in the fruit; hence the work undertaken in 1908, the first
season at Sandusky, was confined almost wholly to sampling and
examining crops of grapes foimd at the various wineries and juice
factories, and to observations of the methods of vinification employed.
A small amoimt of wine was made for technical study. It was un-
fortunate that the investigations could not have been begim at the
opening of the vintage season in 1908, because the crop was especially
good that year for making high-class products, but it was impossible
to make preparations for more extensive operations than those


The samples of fruit secured for 1908 were taken at the various
wine cellars directly from the packages as they arrived at the cellars,
and the name and address of the grower was invariably entered on
the records with each sample. About 4 pounds of fruit were taken
for a sample, and care was taken to secure an average of the crop.
These samples were crushed and pressed by hand in the laboratory
of the Duroy & Haines Co., who kindly furnished facilities for this

The preparation of the samples is a matter of considerable impor-
tance. Experiments on crushing in a mortar by using a pestle, on
crushing by hand in porcelain vessels, and also with small hand
grinders were made. After careful tests by these methods it was
found that crushing by hand is the best method of procuring a sample.
In this way each grape is crushed practically to the same extent, and
the whole mass is reduced to a pulp so much more homogeneous
than by any other method tried, that this one was adopted for all
work during the years 1909 and 1910. The stems were in every case
left in the pulp.

When crushed to a pulp the sample was transferred to a piece of
cheesecloth folded double, spread over a porcelain dish, and the pulp
was pressed by gathering the edges of the cloth firmly in one hand
and gently squeezing the mass until the juice was extracted. The
pulp is in this manner reduced to a ball in the cloth, and by gripping
this firmly with the free hand and applying pressure properly a care-
ful operator can reduce the pulp to about the condition of dryness
arrived at by applying 1,500 pounds direct pressure in a hydrauUc
press. The amount of pressiu-e used will affect considerably the acid
present in the expressed juice; hence care is required in this manipu-
lation to secure comparable results.
5874^— BuU. 145—11 2

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Each sample of juice was then tested as to density with a
Brix spindle, and in most instances a sample was saved for further
examination. These samples for the year 1908 were bottled and
preserved with mercuric chlorid, using tablets purchased at the drug
store, and in this condition they were sent to Stonehenge labora-
tory, Charlottesville, Va., for analysis. The final analyses were
completed by January 5, 1909, and covered only specific gravity,
total solids, sugar-free solids, total sugar, and fixed, volatile, and
total acid. These data were carefully checked, and in the acid de-
terminations allowance was made for the use of the mercuric chlorid
tablets, each of which contained 0.5 gram of mercuric chlorid and 0.57
gram of ammonium chlorid. One tablet was used for 400 cc of fresh
juice. A correction to allow for the acid present in the tablet was
made by deducting 0.075 gram tartaric acid per 100 cc of sample.
Volatile acid was determined on the samples taken in 1908, but the
amount was so slight that it is not reported in the tables; seldom
was 0.01 gram per 100 cc of sample found. During the years 1909
and 1910 volatile acid determinations were not made.

The results on total acid for the samples taken in 1908 are sur-
prisingly low. This was noted as the samples were analyzed, and the
work was carefully checked. The only explanation wliich is suggested
is that during the first season the samples were not pressed sufficiently
to bring out all the acid present. It will be readily understood that
for red wines the acid content secured by crushing and pressing the
fresh fruit will not be the total acid secured by the fermentation of
the pulp and then pressing by power, as is customary in the wineries,
but for white wine the result should be practically the same as when
the fruit is crushed and pressed by power. These pojnts will be
covered and the data given in an additional report on the fermenta-
tion experiments conducted at the Sandusky laboratory.

The preparation of the samples during the years 1909 and 1910
was uniformly by hand as just described; but, having equipped a field
laboratory at Sandusky, the analyses of the juice were made there at
once, as far as possible. In every case the acid was determined by
the titration of the freshly pressed and filtered juice, and a gravity
reading was made on unfiltered juice at the same time, using a Brix
spindle specially made for this work. When the analysis could not
be made promptly a sample was preserved in a pint champagne
bottle with 0.2 gram of mercuric chlorid. The full analysis was
completed usually within from 30 to 60 days after sampling. If the
presence of sucrose was suspected the analysis was made at once, be-
cause experience showed that inversion of this form of sugar occurred
even in the chemically preserved sample.

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The methods of analysis followed are those laid down in Bulletin
No. 107, Revised, Bureau of Chemistry; certain details for which no
explicit directions are given were made to conform to well settled
laboratory practice. Total solids were derived as for wine from the
table given in Bulletin No. 107, Revised (p. 218 et seq.), and the
sugar-free solids by subtracting the total reducing sugar from the
total solids, save in cases where the sample showed sucrose. In such
instances the sugar-free solids were obtained by subtracting the sum
of the reducing sugar and sucrose from the total solids. Subtracting
the total sugar found by inversion when sucrose is present results in
reducing the sugar-free solids below normal.

The add determination was made on filtered juice without previ-
ous heating, by titrating with tenth-normal sodium hydroxid, free
from carbonate, using a neutral solution of azolitmin on a spot plate
as indicator. When the juice was highly colored it was foimd
advantageous to dilute the portion taken about two and one-half
times with recently boiled but cold water, that the reaction might be
more clearly seen.

The sugar determinations were made after the methods of Munson
and Walker (Bulletin No. 107, Revised, p. 241), but it was found pos-
sible to use the gooches twice without cleaning. This was definitely
determined by trial, as shown by the following check resiilts:

Reducing sugar determinations to test need of cleansing gooch before each determination.

[Grams i>er 100 oo.]
Filtered and weighed on clean pad:

White grape juice —

1 21.11

2 21.13

3 21.11

4 21.11

Average 21.12

Red grape juice —

1 16.88

2 16.87

3 16.86

4 16.91

Average 16. 88

Filtered and weighed on 4.3 decigrams cu-
prous oxid:
White grape juice—

5 21.01

6 21.06

7 21.08

8 21.08

Average 21.06

Red grape juice—

6 16.83

6 16.91

7 16.86

8 16.83

Average 16. 86

The Brix readings given are those made on the fresh juice, with a
standardized Brix must spindle especially devised by this laboratory
and corrected to 20® C. in accordance with the regulations of the
Bureau of Standards. The specific gravity readings given were in
every case determined by pyknometer when the sample was analyzed.
These notes apply to the work of 1909 and 1910; some slight variar
tions from this detail occurred diuing the preliminary work of 1908.

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The data for each variety sampled in 1908 are summarized in
Table I, page 20, by bringing the resiilts on all the samples of a
variety from each locality together and giving the average; if more
than one sample was analyzed, the maximum and minimum results
for each locality are shown. The figures presented in this table cover
too few samples to warrant any extended discussion; from several
important locaUties only one sample of a given variety was examined.
This was due to lack of time to organize the work completely for that
year. Further, the data are deficient in that the territory was not
adequately covered. These criticisms, however, do not deprive these
data of value, and, as far as they go, the results show a remarkably
high sugar content in the great majority of the samples analyzed.
In fact, the grape crop was of very good quality that year, and it was
often stated that not in 20 years could such qudity be expected again.
Only one sample of Catawba was analyzed from Middle Bass and one
from North Bass, Ohio, but the Brix readings on the other samples
from these locaUties show that they were all richer in soUd matter
and hence presumably were higher in sugar than the two analyzed.
The importance of the Brix readings of fresh must, as a means by

Online LibraryUnited States. Bureau of ChemistryBulletin - Bureau of Chemistry → online text (page 1 of 97)