Acids. Acids as well as salts and alkalies markedly influence the hydra-
tion capacity of gluten. The hydration capacity of gluten is increased with
increased hydrogen-ion concentration until a pH of 3.0 is reached. With a
pH lower than 3.0 the hydration capacity is decreased. Gortner and
Sharp have shown that the various acids produce a maximum hydration
at pH 3.0. On the acid side of the isoelectric point the gluten is not
dispersed as rapidly as on the alkaline side, so that doughs with an acid
reaction are more tenacious, and not so sticky as ones with an alkaline
reaction. During fermentation of bread the development of acids gives an
acid reaction to the dough, increases the hydration and solubility of the
proteins and thus the tenderness of the resulting bread.
Time of standing. Bailey and Le Vesconte have reported that time of
standing of the dough after mixing influences the extensibility of the
dough. The greater part of this increase in elasticity or ease of handling
is quite noticeable in many dough products. Pastry and other products
are easier to handle if allowed to stand a short time after mixing, before
they are rolled or baked.
Temperature. Bailey and Le Vesconte have reported that temperature
markedly influences the extensibility of a flour and water dough. With
increasing temperature the dough becomes more elastic and less tenacious.
Kent-Jones in reporting the experiments of Luers* comments on the influ-
ence of temperature on hydration capacity. At a temperature of 8° to 9°C.
the imbibition of water by gliadin was quite low and he speaks of it as
almost **an anti-swelling effect." At higher temperatures the gluten becomes
more elastic. This is of great importance in baking, for without this quality
the cell walls of the dough would break and coalesce before the tempera-
ture was reached at which the protein is coagulated. As a result the volume
of the product would either not increase or would be lessened during
baking.
With higher temperatures of mixing the gluten swells more rapidly and
this affects the rapidity with which it develops or becomes attenuated
with mixing.
Swanson in his article, ''The Theory of Colloidal Behavior in Dough,"
gives a good description of dough structure. The following account is
based upon his article, upon other reading, and upon observation.
Bread dough has two continuous phases: water constitutes one, and
gluten the other.
* Luers, H., Koll. Zeitschrift, 25 : Nov., 1919.
422 FLOUR AND BREAD
Starch in dough. When flour is mixed with water to form a dough
the starch granules retain their shape. They also have a certain rigidity and
little adhesive power, so that they are not easily pulled or squeezed out of
shape and do not adhere to each other.
Gluten particles in dough. In contrast to the starch particles in
dough, the gluten particles behave as if their shape is very irregular. In the
flour the shape may be regular, but it is the shape in the dough that gives
the dough part of its distinctive baking properties. On account of this
irregular shape the particles have a very large surface area. When swollen
with water they can be easily pulled, squeezed, or packed into different
shapes.
Page 343
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Acids. Acids as well as salts and alkalies markedly influence the hydra-
tion capacity of gluten. The hydration capacity of gluten is increased with
increased hydrogen-ion concentration until a pH of 3.0 is reached. With a
pH lower than 3.0 the hydration capacity is decreased. Gortner and
Sharp have shown that the various acids produce a maximum hydration
at pH 3.0. On the acid side of the isoelectric point the gluten is not
dispersed as rapidly as on the alkaline side, so that doughs with an acid
reaction are more tenacious, and not so sticky as ones with an alkaline
reaction. During fermentation of bread the development of acids gives an
acid reaction to the dough, increases the hydration and solubility of the
proteins and thus the tenderness of the resulting bread.
Time of standing. Bailey and Le Vesconte have reported that time of
standing of the dough after mixing influences the extensibility of the
dough. The greater part of this increase in elasticity or ease of handling
is quite noticeable in many dough products. Pastry and other products
are easier to handle if allowed to stand a short time after mixing, before
they are rolled or baked.
Temperature. Bailey and Le Vesconte have reported that temperature
markedly influences the extensibility of a flour and water dough. With
increasing temperature the dough becomes more elastic and less tenacious.
Kent-Jones in reporting the experiments of Luers* comments on the influ-
ence of temperature on hydration capacity. At a temperature of 8° to 9°C.
the imbibition of water by gliadin was quite low and he speaks of it as
almost **an anti-swelling effect." At higher temperatures the gluten becomes
more elastic. This is of great importance in baking, for without this quality
the cell walls of the dough would break and coalesce before the tempera-
ture was reached at which the protein is coagulated. As a result the volume
of the product would either not increase or would be lessened during
baking.
With higher temperatures of mixing the gluten swells more rapidly and
this affects the rapidity with which it develops or becomes attenuated
with mixing.
Swanson in his article, ''The Theory of Colloidal Behavior in Dough,"
gives a good description of dough structure. The following account is
based upon his article, upon other reading, and upon observation.
Bread dough has two continuous phases: water constitutes one, and
gluten the other.
* Luers, H., Koll. Zeitschrift, 25 : Nov., 1919.
422 FLOUR AND BREAD
Starch in dough. When flour is mixed with water to form a dough
the starch granules retain their shape. They also have a certain rigidity and
little adhesive power, so that they are not easily pulled or squeezed out of
shape and do not adhere to each other.
Gluten particles in dough. In contrast to the starch particles in
dough, the gluten particles behave as if their shape is very irregular. In the
flour the shape may be regular, but it is the shape in the dough that gives
the dough part of its distinctive baking properties. On account of this
irregular shape the particles have a very large surface area. When swollen
with water they can be easily pulled, squeezed, or packed into different
shapes.