8 BULLETIN 656, U. S. DEPARTMENT OF AGRICULTURE. 
Table 4. — Maxima, minima, and averages of data given in Table 3: Chemical composition 
of hot and cold pressed Concord grape juices. 
Juice pressed before 
or after heating. 
Solids, 
per 
100 cc. 
Sugar 
as in- 
vert 
before 
inver- 
sion, 
per 
100 cc. 
Non- 
sugar 
solids, 
per 
100 cc. 
Total 
acid 
as 
tar- 
taric, 
per 
100 cc. 
Total 
tar- 
taric 
acid, 
free 
and 
com- 
bined, 
per 
100 cc. 
Ash, 
per 
100 cc. 
Alka- 
linity 
of sol- 
uble 
ash, 
N/10 
acid, 
per 
100 cc. 
Alka- 
linity 
of in- 
soluble 
ash, 
N/10 
acid, 
per 
100 cc. 
Free 
tar- 
taric 
acid, 
per 
100 cc. 
Cream 
of 
tartar, 
per 
100 cc. 
Tan- 
nin 
and 
color- 
ing 
mat- 
ter, 
per 
100 CC. 
Maximum: 
Gms. 
17.20 
18.50 
15.66 
16.44 
16.36 
17.43 
Gms. 
14.36 
15.12 
13.38 
13.29 
13.93 
14.03 
Gms. 
2.84 
3.63 
2.25 
3.15 
2.43 
3.40 
Gms. 
0.84 
1.16 
.74 
1.01 
.78 
1.09 
Gms. 
0.65 
1.04 
.55 
.94 
.61 
.99 
Gms. 
0.27 
.46 
.20 
.33 
.23 
.39 
Cc. 
33.2 
55.8 
22.4 
38.0 
26.9 
46.7 
Cc. 
3.6 
4.8 
2.6 
3.8 
3.1 
4.2 
Gms. 
0.24 
.33 
.09 
.12 
.16 
.22 
Gms. 
0.62 
1.05 
.42 
.71 
.50 
.88 
Gms. 
0.08 
.24 
After 
Minimum: 
.06 
.19 
After 
Average: 
Before 
.07 
After 
21 
Average increase. 
1.07 
.10 
.97 
.31 
.38 
.16 
19.8 
1.1 1 .06 
.38 
.14 
Table 4 shows very plainly that during the heating process the 
juice acquires more body, acid constituents, and color. The increase 
in acidity, which is very marked, is due chiefly to the presence of 
cream of tartar and small amounts of other organic acids, principally 
malic and tannic. The increase in nonsugar solids is due to pectin 
substances and gums, coloring matter, and the organic acids just 
mentioned and their salts. These various increases are due to the 
behavior of the skin of the grape berry during the heating process. 
During the storing period the quantity of cream of tartar derived 
through the heating process is largely eliminated through precipita- 
tion (Tables 7 and 8), so that the stored juice contains approxi- 
mately the same amount of this ingredient as is contained in the 
cold-pressed juice. During the storage of the juice, part of the pec- 
tin substances and gums and part of the tannin and coloring matter 
are removed from the juice. With the decrease in cream of tartar 
during storage there is a corresponding decrease in total solids, non- 
sugar solids, total acidity, total tartaric acid, ash, and the alkalinity 
of the water-soluble ash. 
The heating kettles are of aluminum and are steam- jacketed. 
Steam-jacketed, glass-lined steel tanks, or wooden vats fitted with 
aluminum steam coils, may, however, be employed with success. 
The heating kettles, or vats, are equipped with agitators to allow 
uniform heating of the pulp. That thorough agitation while heating 
the crushed fruit is of the utmost importance is self-evident, since 
to allow the mass to rest would overheat the portion next to the 
heating surface and cause scorching. Scorching also results from 
filling the kettles while hot. These two precautions should be closely 
observed in order to avoid a cooked taste in the juice. 
