gjic. Dcpt.

14 i

Issued February 26, 1910.

United States Department of Agriculture,

BUREAU OF CHEMISTRY— Circular No. 51.
H. W. WILEY, Chief of Bureau.

THE VALUE OF PEACHES AS VINEGAR STOCK.

By II. C. GORE,
Assistant Chemist, Division of Foods. «

INTRODUCTION.

The study of the value of peaches as vinegar stock was undertaken
to obtain information in regard to the utilization of surplus peaches.
It has been carried out on a scale sufficiently large to permit of the
results being readily applied to commercial practice. The following
subjects have been considered: (1) The composition of peach juice;
(2) the fermentation of ground peaches and the composition of the
resulting ciders; (3) the preparation and composition of peach vine-
gar; and (4) the chemical changes accompanying the decay of peaches
by Monilia, commonly known as " brown rot " (Sclerotiniafructigena).

THE COMPOSITION OP PEACH JUICE.

The peaches were obtained from different localities to determine
whether or not marked differences in composition exist between the
fruits grown in different sections. Each sample consisted of a six-
basket carrier of fruit weighing about 35 pounds.0 The samples had
been picked when market-ripe — that is, when the fruit was fairly well
colored and filled out, but still firm. Each lot of peaches (with the
exception noted in Table 1 ) was ground by a rotary high-speed apple
grater of the usual form, which readily reduced the peach stones to
small pieces without injury to the knife edges. Samples of the juice
were then obtained by pressing out small portions of the ground fruit
in a cloth, by hand. The analyses given in Table 1 of four lots
of Elberta peaches and two samples of Belle (syn. Belle of Georgia)
indicate that but little variation exists in the composition of the same

<* Except in the case of sample No. 14, which consisted of two half-bushel baskets
fruit.

25241— Cir. 51—10

variety when obtained from different localities. Previous investi-
gations ° of the Department show that the tree-ripe peaches are
materially richer in sugar than the same fruit picked market-ripe,
the average sugar content of three varieties having been found to be
7.50 per cent of the peach pulp in the tree-ripe fruit and 6.04 per
cent in the fruit when market-ripe. The juices reported in Table 1,
therefore, would probably have been richer in sugar if they had been
prepared from tree-ripe instead of from market-ripe fruit. On the
other hand the sugar may have become concentrated during the time
which elapsed between picking and analysis. The analyses there-
fore may be considered fairly to represent the composition of peach

juices from fruit picked when practically mature.

\

TABLE 1. — Composition of the unjermented juices of peaches used in the preparation of

vinegar stock.

No.

Variety and locality where
grown.

Date.

Brix
reading
correct-
ed to
17.5° C.

Corre-
sponding
specific
gravity.

Total
acids as
malic.

Reducing
sugars as
invert.

Total
sugars as
invert.

Sucrose.

2

7
8
14

Elberta, Fort Valley, Ga a . .
Elberta, Richlancl, Ga
Elberta, Baldwin, Ga
Elberta, New York

1909.
July 20
July 24
July 29
Sept. 1

13.17
12.83
14.60
13.37

1. 0535
1. 0520
1.059G
1.0543

Per cent.
0.71
.63
.80

.77

Per cent.
ft 7. 39
5.34
4.81
3.10

Per cent.
8.60
10.21
10.87
9.64

Per cent.
b 1. 15
4.66
5.76
G.20

4

5
10

11
12

Belle (syn. Belle of Georgia),
Fort Valley, Ga.
Belle, Candor, N. C
Waddell, Sleepy Creek,
W. Va.
Carman; Sleepy Creek,W.Va
Mountain Rose, Boonesboro.
Md.

July 20

July 22
Aug. 7

Aug. 7
Aug. 14

13.07

12.82
12.55

12.85
14.19

1.0530

1.0520
1.0508

1. 0521
1.0578

.08

.79
.73

.79
.85

«>9.23

G.19
2.21

2.55
3.31

10.15

9.87
9.73

10.02
10.10

«. 87

3.50
7.15

7.10
6.45

Average

13.27

1. 0539

.75

C3.93

9.91

C5.87

a Pulp crushed by hand.

i> Juice was not expressed from the sample of ground peaches until after yeast had been added. Con-
siderable inversion probably occurred before analysis, owing to the presence of invertase in the yeast,
hence the values lor reducing sugars are too high and those for sucrose too low. These figures are therefore
excluded from the averages.

c Average of seven determinations.

In Table 2 the average composition of these juices is compared
with analyses of peach juices made by others 6 and with the average
composition of apple juice. c The peach juices the analyses of which
are shown in Table 1 are nearly 2 per cent richer in total sugar than
those previously analyzed by others, but are 1 per cent poorer in
sugar than average apple juices. Both series of analyses of peach
juices show that peaches contain much more sucrose than apples and
are also richer in acid.

<*U. S. Dept. Agr., Bureau of Chemistry Bui. 97, p. 21.

b Averaged from the review of literature regarding the composition of peach juices,
given in Bui. 97, p. G.

c Compiled analyses by Van Slyke, New York Agr. Exper. Sta. Bui. 258, p. 449.
[Cir.5l]

TABLE 2. — Average composition of peach juices compared with that of juices of American

apples.

Data.

Total
solids.

Total
acids as
malic.

Reduc-
ing
sugars as
invert.

Total
sugars as
invert.

Sucrose.

Average analysis of peach juices from Table 1

Per cent.
c 13. 27

Per cent.
0.75

Per cent.
/3.93

Per cent.
9.91

Per cent.
/5.87

Average analysis of peach juices taken from the

d 12. 10

« .67

02.01

08. 10

05.79

Average analysis of juices of American apples b

13.52

.52

7.28

10.91

3.45

a Averaged from summary of analyses given in Bureau of Chemistry Bui. 97, p. 6.

b From a compilation of analyses by Van Slyke, New York Agr. Exper. Sta. Bui. 258, p.

c The corrected Brix raading is here assumed to be equal to the per cent of total solids.

449.

e The corrected Brix raading
d Average of five d3terminations.
« Average of three determinations.
/ Average of seven determinations.
g Average of eight determinations.

FERMENTATION OF GROUND PEACHES AND COMPOSITION OF
THE RESULTING CIDERS.

The freshly ground peaches from which small portions had been
taken for preparation of the samples of juice were poured into clean,
open-headed, 5-gallon kegs, each keg was covered loosely with an
oilcloth, and the pulp allowed to ferment either with or without the
addition of a small amount of a vigorous pure culture of yeast. In
most cases yeast was used, as it was desired to insure a prompt and
rapid fermentation. All of the fermentations were conducted at
summer temperatures and were practically completed at the end of
three or four days.

The pulps were pressed immediately after fermentation, except in
two cases in which the pressing was delayed for ten and eleven days,
respectively, on account of the urgency of other work. A powerful
handpower press was used. Racks and cloths were employed, fol-
lowing in this respect standard practice in pressing apple and grape
juice on a commercial scale. In all cases the ciders flowed readily
from the press, the ground peach stones probably assisting to some
extent in the drainage of the press cake. The yields of cider were
determined in the case of the Waddell and Carman varieties with the
following results:

TABLE 3. — Yields of cider from two varieties.

Variety.

Weight
of ground
fruit fer-
mented.

Loss in weight
during fermenta-
tion.

Yield of
pomace.

Yield of juice by
difference.

Waddell

Kg.
16.07
16. 68

Kg.
0.74

.77

Per cent.
4.61
4.62

Kg.

2.61
3.10

Kg.
12.72
12.81

Per cent.
83.0
80.5

Carman

High yields of cider were invariably obtained; the composition of
these products is given in Table 4.

[Cir. 51]

The analyses show that the usual alcoholic fermentation 'had
occurred in all cases. Rather less alcohol was produced than was
expected from the analyses of the juices, but a part of the alcohol
was changed to acetic acid during the fermentation, and a portion of
the substances reducing the alkaline copper tart rate solution, and
hence classed as sugars, was found to be uiifermented. The un-
yeasted samples, Nos! 8 to 14, fermented as rapidly and completely as
the others. The proportion of fixed acid became slightly but dis-
tinctly less during the alcoholic fermentations. The extent of infec-
tion by Monilia is also shown in Table 4, and the analyses of the
ciders indicate that the lots in which brown rot existed fermented
normally.

TABLE 4. — Composition of peach ciders prepared by fermenting peach pulp.

No.

2
7
8

14
4

5

10
11
12

Description of sample.

Inter-
val of
fermen-
tation.

Specific
gravity.

Total
solids.

Total
acid as
malic.

Fixed
acid as
malic.

Volatile
acid as
acetic.

Alco-
hol.

Reduc-
ing sug-
ars as
invert.

Elberta; considerable infec-
tion by brown rot; yeasted..
Elberta; badly infected by
brown rot; yeasted
Elberta; considerable infec-
tion by brown rot; un-
yeasted

Days.
4

3

4
10

4
4

1.0114
(«)

1.0100
1.0111

1.0114
1 0132

P.ct.

P.ct.

P.ct.

P.ct.

P.ct.
4.40

4.12

4.21
3.75

4.34

4.18
4.01
4.11

3.52

P.ct.
0.£5

.57

.62
.31

.38

.33
.20
.16

.61

4. CO
4.94

0.82

1.28
1.27

0.04

.69
.61

0.16

.52

.58

Elberta; no infection by brown
rot; unyeasted

Belle (syn. Belle of Georgia);
slight infection by brown
rot

Belle (syn. Belle of Georgia);
slight infection by brown
rot' yeasted

83

Waddell; no infection by
brown rot; yeasted

3
3

11

1.007G
1.0080

1.0131

3.52
3.69

.77
.94

.54
.69

.60

.15

.07

.30

Carman; no infection by
brown rot; yeasted

Mountain Rose; no brown rot
evident, but badly infected
by peach yellows

Averages

61.0107

c4.19

d.95

«.63

«.30

4.07

.38

a Specific gravity not determined; the average specific gravity of the other three fomented Elberta
peaches has been used in calculating the results to the percentage basis from the basis of grams per 100
cc, on which thay were originally obtained.

6 Average of eight analyses.

c Average of four analyses.

d Average of seven analyses.

e Average of six analyses.

In Table 5 the composition of the peach ciders is shown in com-
parison with the analyses of apple ciders taken from the analytical
data published by Van Slyke. The peach ciders are much higher in
specific gravity, in solids, and in fixed acids than the apple ciders.
They are lower in alcohol, but the juices from which the apple ciders
were prepared were considerably richer in sugars than average apple
juices, containing an average of 13.33 per cent of total sugar ex-
pressed as invert, whereas normal apple juice (see Table 2) contains
but 10.91 per cent of total sugar.

[dr. 51]

TABLE 5. — Comparison of composition of peach and apple ciders (fermented till practi-
cally free from sugar).

Description of sample.

Specific
gravity.

Total
solids.

Fixed
acids as
malic.

Volatile
acids as
acetic.

Alcohol.

Reducing
sugar as
invert.

Peach ciders

1.0107

Per cent.
4.19

Per cent.
0.63

Per cent.
0.30

Per cent.
4.07

Per cent.
0.38

Apple ciders <*

.9932

2.58

.37

.22

G. 59

.26

« Van Slyke, loc. cit., p. 481; selecting the analyses of ciders of experiments 1-11, inclusive, and 21-29,
when the alcohol fermentation was practically complete but before the ciders had become perceptibly
acetified.

THE PREPARATION AND COMPOSITION OF PEACH VINEGAR.

Three lots of vinegar were prepared from mixed peach ciders whose
analyses are given in Table 4, using a small rapid-process generator.0
Well-flavored vinegars were formed, which, however, did not retain
any of the distinctive flavor of the peach. They were clean tasting
and free from woody flavors or objectionable after-tastes, but remained
persistently turbid. Vinegars prepared under the same conditions
from apples would probably have been brilliant.

The average composition of the samples given in Table 6 is com-
pared with that of the apple vinegars given by Van Slyke, the latter
having been prepared from the ciders the average analysis of which is
presented in Table 5. In comparison with the cider vinegars the
peach vinegars are considerably lower hi acid. They are richer in
solids, which is to be expected, since, as shown iix Table 4, peach
ciders are high in unfermented solid matter. The total solids prob-
ably consist largely of material of a gummy nature and are similar
to the unfermentable residues found in vinegar prepared from Kieffer
pears b and from second pressing ciders. c

TABLE 6. — Composition of peach vinegars and comparison with average analysis of apple

vinegar. d

Alka-

linity of

Sample.

Specific
gravity.

Sflids.

Ash.

soluble
ash as
potas-

Reducing
sugar as
invert.

Alcohol.

Volatile
arid as
acetic.

Fixed
acid as
malic.

sium car-

bonate.

Peach vinegars:
No. 1

1. Old

Per cent.
2.64

Per cent.
0.30

Per cent.
0.19

Per cent.
0.44

Per cent.
0. 190

Per cent.
3.89

Per cent.
0.34

No. 2

1. 0227

3.81

.58

.41

.68

.195

4.78

.068

No. 3

1. 0231

3.64

.58

.40

.84

.02

5.21

.127

Averages:

Peach vinegars. . .

1.0206

3. 36

.49

.33

.65

.14

4.C-2

.13

Apple vinegars

1 0°03

1 99

34

.09

7.45

.02

/

a J. Ind. Eng. Chem., 1903, /: 260. *

& J. Amer. Chem. Soc., 1907, 39: 759.

c Ibid., 1906, &8: 202.

<* Van Slyke, loc. cit., prepared from ciders whose average analysis is given in Table 5.

[Cir. 51]

CHEMICAL CHANGES ACCOMPANYING THE DECAY OF PEACHES

BY MONILIA.

In seasons of heavy crops there are available large quantities of
sound, overripe peaches which it will not pay to market as fresh
fruit. Particularly is this the case when hot weather causes the
fruit to ripen rapidly. It is anticipated that the great bulk of peach
vinegar will be made from such fruit, which, while too ripe to ship, is
otherwise essentially sound. As before stated, notes were taken
when the samples of peaches were ground as to the extent of infec-
tion by Monilia, and it was found that the alcoholic fermentation
was not perceptibly influenced. Two special experiments were
undertaken to determine how the presence of a large proportion of
rot would affect the value of peaches as vinegar-making material.
In each, using Mountain Rose and Elberta, respectively, about a
carrier of peaches was inoculated with a pure culture of Monilia by
Mr. W. M. Scott, pathologist in the Bureau of Plant Industry, and
the fruit was allowed to decay for eleven and for ten days. After
the sample had thoroughly rotted the fruit was ground, pressed, and
the juices analyzed. The composition of these juices is shown in
Table 7, contrasted with the analyses of juices from sound fruit of
the same lots. The most conspicuous changes were the inversion of
sucrose and the loss in total sugars. The inversion of the cane
sugar was nearly complete, and the losses in total sugars amounted
to 1.18 and 2.47 per cent or to 11.7 and 25.6 per cent of the total
sugar in the juices of the sound peaches. Small quantities of alcohol
and acetic acid were also formed, probably as a result of fermentation
by yeasts and bacteria.

TABLE 7. — Changes in peach juice due to decay by Monilia.

Description of sample.

Specific
gravity.

Total
acid as
malic.

Volatile
acid as
acetic.

Fixed
acid as
malic.

Reducing
sugar as
invert.

Total
susrar as
invert.

Su-
crose.

Alco-
hol.

Juice of sound peaches:
Mountain Rose

1. 0578

P.ct.

0.85

Per cent.

Per cent.

Per cent.
3.31

Per cent.
10 10

P.ct.

6.45

P.ct.

Elberta

1.0543

.77

c 3.10

9.64

6.20

Juice of rotted peaches:
Mountain Rose

1. 0520

1.02

0.22

0.82

8.52

8.92

.38

0.29

Siberia

1. 0437

.86

.15

.70

6.94

7.17

.20

.40

Samples of vinegar made in the field from peaches rotted in cribs
have been examined by the writer. The juice liberated during decay
was collected in barrels and allowed to go to vinegar. These vine-
gars were generally deficient in acid, many had disagreeable flavors
and after-tastes, and they darkened rapidly on exposure to the
air. Obviously, vinegars should not be made from peaches of this
character.

[Cir. 51]

SUMMARY.

The most important- conclusions to be drawn from this work are,
first, that peaches contain sufficient fermentable sugar for use as
vinegar stock, and, second, that they can be successfully handled by
machinery already in use for making apple cider and vinegar. Other
points of interest are as follows : First, but little variation was found
in the composition of the same variety of peaches when obtained
from different localities. Second, the peach juices analyzed were
found to be richer in sugar than those which have been previously
analyzed by others, but they were about 1 per cent lower in sugar
than average apple juices. They were considerably richer than
apples in sucrose and in acid. Third, it was found that the use of
pure culture yeasts was not necessary to insure rapid alcoholic fer-
mentation. Fourth, the ciders prepared from peaches were con-
siderably poorer in alcohol than apple ciders on account of the fact
that peaches contain less total sugars than apples. Fifth, the pres-
ence of brown rot was found not to interfere with the alcoholic fer-
mentation of the ground peaches, but a large proportion of the sugars
was wasted by allowing the fruit to rot before fermenting. Sixth,
well-flavored vinegars were produced by the use of a small quick-
process generator. These vinegars were of acceptable quality,
though turbid, and did not possess the distinctive peach flavor.

[Cir. 51]

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