most favorable supersaturation for crystal growth, of a sucrose solution
boiled to 112°C., is that between 70° and 90°C. Although crystallization
occurs in a very short time when the sirup is stirred at these temperatures,
the crystals formed are larger than when the sirup is cooled to a lower
temperature. See Figs. 1 and 3. Supersaturation and a low temperature
are desirable for the development of small crystals. The viscosity of a very
supersaturated sirup delays crystal growth.
Temperature at which crystallization occurs. It is a well-known
fact that, in general, chemical precipitates come down more coarsely
crystalline if crystallized at high temperatures. Barium sulfate is a good
example of a substance that crystallizes in large crystals at high tempera-
tures. The sugars follow this general rule. Other things being equal, i.e.,
concentration, etc., the higher the temperature at which crystal formation
occurs, the coarser the crystals formed.
A drop in temperature at first favors the formation of nuclei, and then
hinders it. Crystallization is favored in sugar sirups by cooling to a certain
temperature, but is hindered when cooled to a lower temperature. Since
the viscosity of a saturated sugar solution becomes increasingly greater as
the temperature falls below 70°C., crystal formation is also slower as the
temperature falls.
Agitation. Stirring a solution favors the formation of nuclei and
hinders the depositing of the material of the solution on the nuclei already
formed. Hence, crystals in solutions that are stirred do not develop to
the size that they do in spontaneous crystallization. Bancroft states that
"The mean size of crystals is determined by the total amount of the
material crystallizing and number of crystals. The really important thing
therefore is the number of nuclei which are formed under any given
conditions." If small crystals are desired, then the conditions should be such
that many nuclei are formed. Small crystals are obtained in sirups of
definite concentration and temperature, if the sirup is stirred until the
mass is kneadable. However, if the sirup is stirred for only a short time,
some nuclei are formed, but after agitation is stopped, the formation oi
new nuclei is not favored and crystal growth is favored. Fig. 2 shows
crystals from fondant stirred for only a few seconds. The crystals are
much larger than those in Fig. 1, which shows crystals from fondant that
was stirred until the mass could be kneaded. The same thing is illustrated
in Fig. 10, which shows crystals from divinity that would not quite hold
its shape but spread when dropped on oil paper. The crystals from the same
divinity (Fig. 9) which was stirred until it would hold its shape, but was
glossy and not dry in appearance when dropped on oil paper, are small.
Divinity with the small crystals is very smooth and velvety on the palate.
This emphasizes the importance of stirring candy and icing sirups until
practically all the material is crystallized, if small crystals are desired.
Adsorption and impurities in the solution. Freundlich states that
*'in the vast majority of cases the foreign substance lowers the rate of
52 SUGAR COOKERY
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most favorable supersaturation for crystal growth, of a sucrose solution
boiled to 112°C., is that between 70° and 90°C. Although crystallization
occurs in a very short time when the sirup is stirred at these temperatures,
the crystals formed are larger than when the sirup is cooled to a lower
temperature. See Figs. 1 and 3. Supersaturation and a low temperature
are desirable for the development of small crystals. The viscosity of a very
supersaturated sirup delays crystal growth.
Temperature at which crystallization occurs. It is a well-known
fact that, in general, chemical precipitates come down more coarsely
crystalline if crystallized at high temperatures. Barium sulfate is a good
example of a substance that crystallizes in large crystals at high tempera-
tures. The sugars follow this general rule. Other things being equal, i.e.,
concentration, etc., the higher the temperature at which crystal formation
occurs, the coarser the crystals formed.
A drop in temperature at first favors the formation of nuclei, and then
hinders it. Crystallization is favored in sugar sirups by cooling to a certain
temperature, but is hindered when cooled to a lower temperature. Since
the viscosity of a saturated sugar solution becomes increasingly greater as
the temperature falls below 70°C., crystal formation is also slower as the
temperature falls.
Agitation. Stirring a solution favors the formation of nuclei and
hinders the depositing of the material of the solution on the nuclei already
formed. Hence, crystals in solutions that are stirred do not develop to
the size that they do in spontaneous crystallization. Bancroft states that
"The mean size of crystals is determined by the total amount of the
material crystallizing and number of crystals. The really important thing
therefore is the number of nuclei which are formed under any given
conditions." If small crystals are desired, then the conditions should be such
that many nuclei are formed. Small crystals are obtained in sirups of
definite concentration and temperature, if the sirup is stirred until the
mass is kneadable. However, if the sirup is stirred for only a short time,
some nuclei are formed, but after agitation is stopped, the formation oi
new nuclei is not favored and crystal growth is favored. Fig. 2 shows
crystals from fondant stirred for only a few seconds. The crystals are
much larger than those in Fig. 1, which shows crystals from fondant that
was stirred until the mass could be kneaded. The same thing is illustrated
in Fig. 10, which shows crystals from divinity that would not quite hold
its shape but spread when dropped on oil paper. The crystals from the same
divinity (Fig. 9) which was stirred until it would hold its shape, but was
glossy and not dry in appearance when dropped on oil paper, are small.
Divinity with the small crystals is very smooth and velvety on the palate.
This emphasizes the importance of stirring candy and icing sirups until
practically all the material is crystallized, if small crystals are desired.
Adsorption and impurities in the solution. Freundlich states that
*'in the vast majority of cases the foreign substance lowers the rate of
52 SUGAR COOKERY