Halliday and Bailey have reported that the addition of calcium chloride
favors jelly formation, as somewhat lower concentrations of pectin, acid,
and sugar are required when it is added. On the acid side, sodium chloride
tends to prevent jelly formation, i.e., larger quantities of acid and sugar
are required when sodium chloride is added. Spencer has reported that on
the alkaline side sodium chloride tends to precipitate the pectin. Spencer
has also reported that, with the same anion, chlorine, the precipitating effect
of the cation increased with increasing valence, or Al > Ca > Na. With
164 JELLY
the same cation but different anions Spencer gives the order of absorption
of the negative ion by pectin as acetate > citrate > tartrate. This means
that the tartrate is not so strongly adsorbed as the citrate or acetate ions,
hence has less stabilizing effect and is more easily precipitated by sugar.
The chloride anion is more strongly absorbed than the nitrate or sulfate
ions.
Salts buffer a fruit juice so that more acid is required to give a definite
pH when salts are present. But the hydrogen ion is not the only positive
ion in the fruit juice. Myers and Baker have found that the cation of the
salt may supplement the hydrogen ion, but only at definite hydrogen-ion
concentrations. No jelly was formed with added salts above pK 3.6. Thus
jellies from fruit juices may have a slightly wider range of hydrogen-ion
concentration for jelly formation than those from pure water, acid, pectin,
and sugar. Myers and Baker used sulfuric, tartaric, and citric acids and
the sodium salts of these acids in their investigations.
The negatively charged ion of a salt tends to stabilize pectin sols, but
those anions absorbed most strongly exert the most stabilizing effect. These
negatively charged anions may be neutralized by the positively charged ion
of a salt, but the adsorption of cations also varies, so that some have a
greater destabilizing effect than others. Since all pectins contain salts, the
quantitative recipes worked out for one pectin may not give exactly the
same results with other pectins because of a different salt content.
The Role of Sugar in Jelly Formation
Sugar, if its concentration and that of acid and pectin is sufficient, pre-
cipitates the pectin. Spencer explains this precipitation as follows. When a
pectin sol is formed, *'an equilibrium is reached between the partial pressure
of the adsorbed water" of the pectin *'and that in the dispersing medium."
When sugar is added to the pectin sol, this equilibrium is disturbed, for
when the sugar dissolves in the dispersion medium it lowers the vapor
pressure of the dispersing medium. As a result the pectin particles lose
water and are less stable. Increases in sugar accelerate the setting of the
jelly, probably because of increased dehydration, although rate of setting
is also modified by other factors.
Jelly without added sugar. Jelly can be made by boiling down some
fruit juices until they yield a ''jelly test." The concentration of 2 cups of
gooseberry juice yields less than ^ cup of gummy, tough, sticky jelly. If
left with the lid off for a few days it becomes dry enough to handle. It
is very dark in color, looking and feeling very much like licorice candy.
The fruit flavor is present, although scarcely noticeable at first, because of
the extremely acid taste.
Page 133
Presented as published in 1932. Historical recipes may not meet modern food-safety standards. Cook from the modern interpretation, not the original instructions.
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Halliday and Bailey have reported that the addition of calcium chloride
favors jelly formation, as somewhat lower concentrations of pectin, acid,
and sugar are required when it is added. On the acid side, sodium chloride
tends to prevent jelly formation, i.e., larger quantities of acid and sugar
are required when sodium chloride is added. Spencer has reported that on
the alkaline side sodium chloride tends to precipitate the pectin. Spencer
has also reported that, with the same anion, chlorine, the precipitating effect
of the cation increased with increasing valence, or Al > Ca > Na. With
164 JELLY
the same cation but different anions Spencer gives the order of absorption
of the negative ion by pectin as acetate > citrate > tartrate. This means
that the tartrate is not so strongly adsorbed as the citrate or acetate ions,
hence has less stabilizing effect and is more easily precipitated by sugar.
The chloride anion is more strongly absorbed than the nitrate or sulfate
ions.
Salts buffer a fruit juice so that more acid is required to give a definite
pH when salts are present. But the hydrogen ion is not the only positive
ion in the fruit juice. Myers and Baker have found that the cation of the
salt may supplement the hydrogen ion, but only at definite hydrogen-ion
concentrations. No jelly was formed with added salts above pK 3.6. Thus
jellies from fruit juices may have a slightly wider range of hydrogen-ion
concentration for jelly formation than those from pure water, acid, pectin,
and sugar. Myers and Baker used sulfuric, tartaric, and citric acids and
the sodium salts of these acids in their investigations.
The negatively charged ion of a salt tends to stabilize pectin sols, but
those anions absorbed most strongly exert the most stabilizing effect. These
negatively charged anions may be neutralized by the positively charged ion
of a salt, but the adsorption of cations also varies, so that some have a
greater destabilizing effect than others. Since all pectins contain salts, the
quantitative recipes worked out for one pectin may not give exactly the
same results with other pectins because of a different salt content.
The Role of Sugar in Jelly Formation
Sugar, if its concentration and that of acid and pectin is sufficient, pre-
cipitates the pectin. Spencer explains this precipitation as follows. When a
pectin sol is formed, *'an equilibrium is reached between the partial pressure
of the adsorbed water" of the pectin *'and that in the dispersing medium."
When sugar is added to the pectin sol, this equilibrium is disturbed, for
when the sugar dissolves in the dispersion medium it lowers the vapor
pressure of the dispersing medium. As a result the pectin particles lose
water and are less stable. Increases in sugar accelerate the setting of the
jelly, probably because of increased dehydration, although rate of setting
is also modified by other factors.
Jelly without added sugar. Jelly can be made by boiling down some
fruit juices until they yield a ''jelly test." The concentration of 2 cups of
gooseberry juice yields less than ^ cup of gummy, tough, sticky jelly. If
left with the lid off for a few days it becomes dry enough to handle. It
is very dark in color, looking and feeling very much like licorice candy.
The fruit flavor is present, although scarcely noticeable at first, because of
the extremely acid taste.