Relation of the time factor to optimum acidity. Olsen assumed
that the lowering of jelly strength might be caused by incomplete dehydra-
tion of the pectin and lessened precipitation or by a more flexible network
of pectin. To test the second postulate he prepared jellies by heating the
pectin to 55°C. and to boiling. The jelly at 55° was made as follows: The
pectin, 30 grams of sugar, and water to make a total weight of 140 grams
were brought to 36°C. The minimum amount of acid, the remaining sugar,
and water were boiled together, cooled to 65°C., and adjusted to correct
weight with distilled water. The additional acid and the pectin solution
were added and stirred, the time was varied from the moment the pectin
solution was poured into the warm sirup until the mixture was poured in
jelly glasses, as shown in Table 22. The strength was tested with a Tarr
and Baker jelly strength tester. Olsen states that a high-grade pectin made
by the standardized hot method gives a reading close to 45.
The optimum pH varies with the time factor. The principal variation is
the rate of gelation of the pectin as influenced by the acid concentration.
Olsen explains this as follows: "The largest or 'optimum' amount of the
acid to be used will be that point at which an additional increase in acid
will increase the rate of setting to a point where loss in jelly strength due to
a disturbance of the jelly in the stirring or pouring exactly balances the
strengthening effect of that same increment of acid." Or in other words,
stirring or pouring hinders jelly formation, which is offset by increasing
the hydrogen-ion concentration.
Acids in fruits. The acids occurring naturally in fruit juices that
are used for jelly are tartaric, malic, and citric. Sometimes acetic acid is
162
JELLY
TABLE 22
The Relation of the Time Factor to Optimum Acidity. (Olsen)
(The time indicated is the interval between the pouring of the pectin solution
into the sugar sirup and the pouring of the mixture into glasses. Jellies contain
60 per cent of sugar, 2.5 grams of apple pectin 119°F., phosphoric acid as in-
dicated. Temperature of pectin solution 36°C.; of sugar solution 65°C.; of final
mixture 55°C.) (Olsen)
Series
B
Series C
Series
D
25% phos-
90 seconds
50 seconds
8 secon
ds
phoric acid
solution
cc.
Jelly
Strength
pH
Jelly
strength
^H
Jelly
Strength
pH
0.26
0.0
3.27
0.36
33.0
3.10
36^5
3.13
0.56
69.0
2.80
67.0
2.88
0.86
80.0
2.50
0.96
41.0
2.39
....
....
115.0
2.40
1.06
....
75.0
2.37
1.26
61.5
2.24
1.56
19.0
2.13
120.0
2.13
1.96
14.5
2.03
28.5
2.00
145.0
2.01
3.96
....
135.0
1.76
added to apple juice to make spiced apple jelly. Tarr's results show that
acetic acid is of little value to add to a juice to increase its jellying power,
because it volatilizes during boiling and is only slightly ionized in solution.
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Relation of the time factor to optimum acidity. Olsen assumed
that the lowering of jelly strength might be caused by incomplete dehydra-
tion of the pectin and lessened precipitation or by a more flexible network
of pectin. To test the second postulate he prepared jellies by heating the
pectin to 55°C. and to boiling. The jelly at 55° was made as follows: The
pectin, 30 grams of sugar, and water to make a total weight of 140 grams
were brought to 36°C. The minimum amount of acid, the remaining sugar,
and water were boiled together, cooled to 65°C., and adjusted to correct
weight with distilled water. The additional acid and the pectin solution
were added and stirred, the time was varied from the moment the pectin
solution was poured into the warm sirup until the mixture was poured in
jelly glasses, as shown in Table 22. The strength was tested with a Tarr
and Baker jelly strength tester. Olsen states that a high-grade pectin made
by the standardized hot method gives a reading close to 45.
The optimum pH varies with the time factor. The principal variation is
the rate of gelation of the pectin as influenced by the acid concentration.
Olsen explains this as follows: "The largest or 'optimum' amount of the
acid to be used will be that point at which an additional increase in acid
will increase the rate of setting to a point where loss in jelly strength due to
a disturbance of the jelly in the stirring or pouring exactly balances the
strengthening effect of that same increment of acid." Or in other words,
stirring or pouring hinders jelly formation, which is offset by increasing
the hydrogen-ion concentration.
Acids in fruits. The acids occurring naturally in fruit juices that
are used for jelly are tartaric, malic, and citric. Sometimes acetic acid is
162
JELLY
TABLE 22
The Relation of the Time Factor to Optimum Acidity. (Olsen)
(The time indicated is the interval between the pouring of the pectin solution
into the sugar sirup and the pouring of the mixture into glasses. Jellies contain
60 per cent of sugar, 2.5 grams of apple pectin 119°F., phosphoric acid as in-
dicated. Temperature of pectin solution 36°C.; of sugar solution 65°C.; of final
mixture 55°C.) (Olsen)
Series
B
Series C
Series
D
25% phos-
90 seconds
50 seconds
8 secon
ds
phoric acid
solution
cc.
Jelly
Strength
pH
Jelly
strength
^H
Jelly
Strength
pH
0.26
0.0
3.27
0.36
33.0
3.10
36^5
3.13
0.56
69.0
2.80
67.0
2.88
0.86
80.0
2.50
0.96
41.0
2.39
....
....
115.0
2.40
1.06
....
75.0
2.37
1.26
61.5
2.24
1.56
19.0
2.13
120.0
2.13
1.96
14.5
2.03
28.5
2.00
145.0
2.01
3.96
....
135.0
1.76
added to apple juice to make spiced apple jelly. Tarr's results show that
acetic acid is of little value to add to a juice to increase its jellying power,
because it volatilizes during boiling and is only slightly ionized in solution.