Bread during baking tends to attain a physico-chemical equilibrium. But
the temperature attained during baking is much higher than the storage
temperature. Freshly baked bread does not taste or feel like bread 24 hours
old. Bread can be stored so that it loses no moisture, yet readjustments in
the loaf take place, so that staling occurs. If bread is stored at temperatures
of 60°C. or above, the texture remains more like that of freshly baked
bread and staling is not perceptible. But at this temperature bacterial
changes occur readily. If the bread has not lost considerable moisture, upon
reheating it, it acquires the characteristics of freshly baked bread.
The principle of Le Chatelier gives the factors of equilibrium: ''Every
system in chemical equilibrium, under the influence of a change of any
single one of the factors of equilibrium, undergoes a transformation in
such direction that, if this transformation took place alone, it vv^ould pro-
duce a change in the opposite direction of the factor in question. The
factors of equilibrium are temperature, pressure and electromotive force,
corresponding to three forms of energy; heat, electricity and mechanical
energy."
Hydrogen-Ion Concentration
The symbol pH is very commonly used in present-day literature. Some
explanation of the term and its relation to hydrogen-ion concentration is
desirable. Perhaps it w^ill be best to review briefly what is meant by hydro-
gen-ion concentration. In a solution of hydrochloric acid in water, the
molecule of the acid consists of an atom of hydrogen united to an atom of
chlorine. Hydrochloric acid molecules are found in the solution, but not all
the acid remains in the molecular form. Part of the acid molecules are
ionized into hydrogen ions and chlorine ions, the degree of ionization de-
pending upon the concentration, the more dilute the acid solution the
greater the percentage of hydrochloric acid ionized. The hydrogen ions are
positively charged, and the chlorine ions are negatively charged. In symbols,
the ionization of hydrochloric acid is expressed as follows:
HCl 1==; H+ + Cl-
When a substance is ionized in solution the solution conducts an elec-
trical current.
When water is ionized it gives both hydrogen ions and hydroxyl ions.
Since the ionization of water is very slight, the amount of hydrogen and
hydroxyl ions in a liter of water is not great.
H2O tzzzz; H+ + OH-
In pure water the concentration of hydrogen ions and hydroxyl ions is
HYDROGEN-ION CONCENTRATION 27
equal at 22°C. The reaction of water varies at various temperatures, so
that the following discussion is confined to room temperature or 22 °C. The
concentration of the hydrogen ions and hydroxyl ions is of a
10,000,000
gram-molecular weight (mole) each per liter. A normal solution of hydro-
gen ions contains 1 gram-molecular weight (1 gram) of hydrogen ions per
liter of solution; a normal solution of hydroxyl ions contains 1 gram-
molecular weight (17 grams) of hydroxyl ions per liter of solution. A liter
of pure water contains of a mole of hydrogen. This requires
10,000,000
many figures to express as a fraction, so for convenience the concentration
is expressed as follows : ^^ = 10"'^. Again for convenience Sorensen
proposed to disregard the minus sign and use the numerical value of the
exponent 10 to express the reaction corresponding to the concentration of
hydrogen ions.
Page 26
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.
Bread during baking tends to attain a physico-chemical equilibrium. But
the temperature attained during baking is much higher than the storage
temperature. Freshly baked bread does not taste or feel like bread 24 hours
old. Bread can be stored so that it loses no moisture, yet readjustments in
the loaf take place, so that staling occurs. If bread is stored at temperatures
of 60°C. or above, the texture remains more like that of freshly baked
bread and staling is not perceptible. But at this temperature bacterial
changes occur readily. If the bread has not lost considerable moisture, upon
reheating it, it acquires the characteristics of freshly baked bread.
The principle of Le Chatelier gives the factors of equilibrium: ''Every
system in chemical equilibrium, under the influence of a change of any
single one of the factors of equilibrium, undergoes a transformation in
such direction that, if this transformation took place alone, it vv^ould pro-
duce a change in the opposite direction of the factor in question. The
factors of equilibrium are temperature, pressure and electromotive force,
corresponding to three forms of energy; heat, electricity and mechanical
energy."
Hydrogen-Ion Concentration
The symbol pH is very commonly used in present-day literature. Some
explanation of the term and its relation to hydrogen-ion concentration is
desirable. Perhaps it w^ill be best to review briefly what is meant by hydro-
gen-ion concentration. In a solution of hydrochloric acid in water, the
molecule of the acid consists of an atom of hydrogen united to an atom of
chlorine. Hydrochloric acid molecules are found in the solution, but not all
the acid remains in the molecular form. Part of the acid molecules are
ionized into hydrogen ions and chlorine ions, the degree of ionization de-
pending upon the concentration, the more dilute the acid solution the
greater the percentage of hydrochloric acid ionized. The hydrogen ions are
positively charged, and the chlorine ions are negatively charged. In symbols,
the ionization of hydrochloric acid is expressed as follows:
HCl 1==; H+ + Cl-
When a substance is ionized in solution the solution conducts an elec-
trical current.
When water is ionized it gives both hydrogen ions and hydroxyl ions.
Since the ionization of water is very slight, the amount of hydrogen and
hydroxyl ions in a liter of water is not great.
H2O tzzzz; H+ + OH-
In pure water the concentration of hydrogen ions and hydroxyl ions is
HYDROGEN-ION CONCENTRATION 27
equal at 22°C. The reaction of water varies at various temperatures, so
that the following discussion is confined to room temperature or 22 °C. The
concentration of the hydrogen ions and hydroxyl ions is of a
10,000,000
gram-molecular weight (mole) each per liter. A normal solution of hydro-
gen ions contains 1 gram-molecular weight (1 gram) of hydrogen ions per
liter of solution; a normal solution of hydroxyl ions contains 1 gram-
molecular weight (17 grams) of hydroxyl ions per liter of solution. A liter
of pure water contains of a mole of hydrogen. This requires
10,000,000
many figures to express as a fraction, so for convenience the concentration
is expressed as follows : ^^ = 10"'^. Again for convenience Sorensen
proposed to disregard the minus sign and use the numerical value of the
exponent 10 to express the reaction corresponding to the concentration of
hydrogen ions.