Some of the less acid fruit juices do not increase the acidity of the gelatin
mixture as much as the lemon juice. The addition of fruit or vegetable
juices such as tomato juice may bring the pH of the gelatin close to its
isoelectric point. The pH of tomato juice varies somewhat but is usually
between 4.2 and 4.8. The juices that bring the gelatin close to the isoelec-
tric point do not increase the time required for gelation to the extent that
the lemon juice does. Gelatin made with tomato juice varies in the length
of time required for setting. But in recipes lemon juice is usually added
in combination with other fruit juices, and either lemon or vinegar is
often added with tomato juice for tomato gelatins. Recipes containing a
SUGAR 185
larger quantity of a very acid fruit juice may need a higher concentration
of gelatin to produce a texture desired for serving.
Lemon jellies were made from the same sample of gelatin, using different
proportions of lemon juice. When the quantity of lemon juice added Vi^as
just sufficient to bring the hydrogen-ion concentration of the mixture to
about pH 4.7, the isoelectric point of gelatin, the jelly formed w^as cloudy
and more turbid than when the pH of the mixture was lower than 4.7.
Jellies with a pH lower than the isoelectric point of gelatin were clear
and sparkling. They also required a longer time for the gel to form than
those with a higher pH. When the series was repeated but citric acid was
substituted for lemon juice, similar results were obtained.
Tartaric acid added to the gelatin solution also increases the time for
gelation. A teaspoon of tartaric acid (about 3.5 grams) or a teaspoon of
citric acid (about 3.5 grams) added to 3.5 grams of gelatin and 236.5 cc.
of water gives the mixture about />H 2.7. The jellies are clear and tart.
Patten and Johnson have reported that a 3 per cent solution of gelatin
at 20° to 22°C. begins to liquefy between a pH of 8.4 and a pH of 9.2.
It is not completely fluid at />H 9.6.
Salts. It has been reported by several investigators that the gelation tem-
perature is affected by electrolytes. The effect is usually given as follows
for anions at equal concentrations. The first of the series elevates the
gelation temperature, and it is slightly lower for each following anion,
until the iodide may lower the gelation temperature below 0°C. SO4 >
citrate > tartrate > acetate > CI > CIO3 > NO3 > Br > I. This is the
order above the isoelectric point. When enough lemon juice or acid has been
added so that the reaction is below the isoelectric point the cations may have
more effect than the anions. The order of anions given above indicates that
some salts would increase the tenderness of gelatin gels whereas others
would increase the gel strength.
Page 150
Presented as published in 1932. Historical recipes may not meet modern food-safety standards. Cook from the modern interpretation, not the original instructions.
AI-modernized reading of the original text
A modernized reading is not available for this page yet. You are seeing the original text.
Some of the less acid fruit juices do not increase the acidity of the gelatin
mixture as much as the lemon juice. The addition of fruit or vegetable
juices such as tomato juice may bring the pH of the gelatin close to its
isoelectric point. The pH of tomato juice varies somewhat but is usually
between 4.2 and 4.8. The juices that bring the gelatin close to the isoelec-
tric point do not increase the time required for gelation to the extent that
the lemon juice does. Gelatin made with tomato juice varies in the length
of time required for setting. But in recipes lemon juice is usually added
in combination with other fruit juices, and either lemon or vinegar is
often added with tomato juice for tomato gelatins. Recipes containing a
SUGAR 185
larger quantity of a very acid fruit juice may need a higher concentration
of gelatin to produce a texture desired for serving.
Lemon jellies were made from the same sample of gelatin, using different
proportions of lemon juice. When the quantity of lemon juice added Vi^as
just sufficient to bring the hydrogen-ion concentration of the mixture to
about pH 4.7, the isoelectric point of gelatin, the jelly formed w^as cloudy
and more turbid than when the pH of the mixture was lower than 4.7.
Jellies with a pH lower than the isoelectric point of gelatin were clear
and sparkling. They also required a longer time for the gel to form than
those with a higher pH. When the series was repeated but citric acid was
substituted for lemon juice, similar results were obtained.
Tartaric acid added to the gelatin solution also increases the time for
gelation. A teaspoon of tartaric acid (about 3.5 grams) or a teaspoon of
citric acid (about 3.5 grams) added to 3.5 grams of gelatin and 236.5 cc.
of water gives the mixture about />H 2.7. The jellies are clear and tart.
Patten and Johnson have reported that a 3 per cent solution of gelatin
at 20° to 22°C. begins to liquefy between a pH of 8.4 and a pH of 9.2.
It is not completely fluid at />H 9.6.
Salts. It has been reported by several investigators that the gelation tem-
perature is affected by electrolytes. The effect is usually given as follows
for anions at equal concentrations. The first of the series elevates the
gelation temperature, and it is slightly lower for each following anion,
until the iodide may lower the gelation temperature below 0°C. SO4 >
citrate > tartrate > acetate > CI > CIO3 > NO3 > Br > I. This is the
order above the isoelectric point. When enough lemon juice or acid has been
added so that the reaction is below the isoelectric point the cations may have
more effect than the anions. The order of anions given above indicates that
some salts would increase the tenderness of gelatin gels whereas others
would increase the gel strength.