mum stiffening power until a higher temperature is reached. Thus Alsberg
and Rask found the maximum viscosity of wheat starch occurred at 95 °C.
Woodruff and Webber have shown that a 5 per cent wheat starch paste
must be heated to at least 90°C. before the resulting gels will form mold-
able gels, such as would be served for puddings. Furthermore, rapid heating
to this temperature gave a better-formed gel than did slow heating. But
temperatures of 95 °C. or above gave the firmest gels obtained with this
concentration.
For cornstarch paste Alsberg and Rask found the maximum viscosity at
91 °C., but Richardson, Higginbotham, and Farrow's results indicate that
maximum swelling of some cornstarch pastes does not occur until a tem-
perature of 100°C. is reached.
Degree of grinding. Samec states: ''The capacity of a starch to form paste
decreases with continued grinding of the starch and the grinding also
peptizes the starch to such an extent that it can pass through ultra-filters."
Alsberg found that in flour ground until the granule walls are broken a
larger percentage of the starch is dispersed. A higher percentage of such
flour is required to produce a paste of definite thickness. His explanation
of this is that starch from the broken granules passes into solution and does
not thicken as much, hence a greater quantity is needed to produce a paste,
for there are fewer whole granules to swell and occupy the volume of the
suspension and thus produce stiffening or thickening. During gelatinization
starch may absorb about 30 times its w^eight in water. The smaller the
number of granules broken or dispersed, the smaller the percentage of
starch required to produce a paste of definite stiffness.
The proportion of alpha- and beta-amylose. Samec says that paste forma-
tion depends on having a proper balance between the tendency to associate
and to hydrate. With potato starch, and starches from similar species, this
relationship is attained by the presence of both amylo-amylose and erythro-
amylose, and by esterfication of the polysaccharid with phosphoric acid.
Length of the starch chain. Richardson, Higginbotham, and Farrow state
that Staudinger has shown that for many types of long-chain polymers there
is close correlation between the chain length and the viscosity of the solu-
tion. This relation was found to hold with sago starches but with other
starches the relation was not found, so that it was suggested that other
factors, such as distribution of length, rate of gelatinization, and degree of
hydration of the chain molecules are as important as chain length in deter-
mining viscosity. Natural starches contain chains of varying lengths and it
may be that the average chain length is greater for some species of starches
than for others. However, it is known that dextrins have shorter chain
lengths than starch, and they have little or no paste-forming properties.
When starch is dextrinized by heat or broken into shorter chain lengths
by hydrolysis, either by diastase, acid, or other means, the stiffening power
is decreased. Thus more of browned flour is required for thickening gravies
and sauces than of the unbrowned flour.
RESULTS OF FINE OR OVER-GRINDING ON FLOUR 411
Page 333
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mum stiffening power until a higher temperature is reached. Thus Alsberg
and Rask found the maximum viscosity of wheat starch occurred at 95 °C.
Woodruff and Webber have shown that a 5 per cent wheat starch paste
must be heated to at least 90°C. before the resulting gels will form mold-
able gels, such as would be served for puddings. Furthermore, rapid heating
to this temperature gave a better-formed gel than did slow heating. But
temperatures of 95 °C. or above gave the firmest gels obtained with this
concentration.
For cornstarch paste Alsberg and Rask found the maximum viscosity at
91 °C., but Richardson, Higginbotham, and Farrow's results indicate that
maximum swelling of some cornstarch pastes does not occur until a tem-
perature of 100°C. is reached.
Degree of grinding. Samec states: ''The capacity of a starch to form paste
decreases with continued grinding of the starch and the grinding also
peptizes the starch to such an extent that it can pass through ultra-filters."
Alsberg found that in flour ground until the granule walls are broken a
larger percentage of the starch is dispersed. A higher percentage of such
flour is required to produce a paste of definite thickness. His explanation
of this is that starch from the broken granules passes into solution and does
not thicken as much, hence a greater quantity is needed to produce a paste,
for there are fewer whole granules to swell and occupy the volume of the
suspension and thus produce stiffening or thickening. During gelatinization
starch may absorb about 30 times its w^eight in water. The smaller the
number of granules broken or dispersed, the smaller the percentage of
starch required to produce a paste of definite stiffness.
The proportion of alpha- and beta-amylose. Samec says that paste forma-
tion depends on having a proper balance between the tendency to associate
and to hydrate. With potato starch, and starches from similar species, this
relationship is attained by the presence of both amylo-amylose and erythro-
amylose, and by esterfication of the polysaccharid with phosphoric acid.
Length of the starch chain. Richardson, Higginbotham, and Farrow state
that Staudinger has shown that for many types of long-chain polymers there
is close correlation between the chain length and the viscosity of the solu-
tion. This relation was found to hold with sago starches but with other
starches the relation was not found, so that it was suggested that other
factors, such as distribution of length, rate of gelatinization, and degree of
hydration of the chain molecules are as important as chain length in deter-
mining viscosity. Natural starches contain chains of varying lengths and it
may be that the average chain length is greater for some species of starches
than for others. However, it is known that dextrins have shorter chain
lengths than starch, and they have little or no paste-forming properties.
When starch is dextrinized by heat or broken into shorter chain lengths
by hydrolysis, either by diastase, acid, or other means, the stiffening power
is decreased. Thus more of browned flour is required for thickening gravies
and sauces than of the unbrowned flour.
RESULTS OF FINE OR OVER-GRINDING ON FLOUR 411