somewhat larger stresses. Plasticity is thus a complex property, made up
of two independent factors, which we must evaluate separately." Modeling
clay is plastic. Plasticity is an important property of fats used for cakes,
biscuits, and pastry. A plastic fat has a consistency such that it will form
a thin sheet or layer in a batter or it will retain air bubbles when
''creamed." The enclosing of these air bubbles in the fat is an aid in leaven-
ing cakes and may assist in obtaining a velvety texture, for the enclosing
of the air renders the fat more plastic, thus more easily distributed in the
batter at lower temperatures.
Energetics
Burns states, "Energy is the underlying cause of all changes in matter.
This does not seem a very satisfactory definition, but, so far, it is the only
one possible. . . . Energy, then, is that which produces an effect on our
senses." It is measured by its power to do work.
Energy in some form is often applied to the materials used for food
products. This energy may be electrical, mechanical, or in the form of heat.
An electric current passed through a food may be used to cook it. Very
interesting experiments are being carried out along this line of work by the
Household Equipment Department at Iowa State College. One of the
striking results is the very short time required to cook the food. The pas-
sage of an electric current is used by some companies to pasteurize milk
and by some to sterilize fruit juices.
Mechanical energy is used to beat, stir, fold, knead, or grind food.
The frequency of application of heat to foods does not need to be men-
tioned, for this is what the term to cook means. Foods may be cooked by
radiant heat; or by transmission of the heat by conduction, i.e., from parti-
cle to particle ; or by convection, which is the diffusion of heat through a gas
or liquid by movement of the gas or liquid particles. A combination of these
methods may be used to transmit the heat. Oven cooking employs all three.
Kinetic energy is due to motion. It may be due to motion of the sub-
stance itself or of the particles composing it. It is directly available for
work. Potential energy is associated with position, i.e., composition, stress,
or strain. Kinetic energy is necessary to liberate it to perform work.
Just as matter is indestructible, though its form may be changed, so is
energy indestructible. This constitutes the first law of thermodynamics.
The law of Hess states that the amount of heat generated by a chemical
reaction is the same whether it takes place all at once or in steps.
The second law of thermodynamics concerns the degradation or dissipa-
tion of energy. In practise, some of the freed energy is converted into heat,
which is diffused among the surrounding objects, and, so far as work is
concerned, is lost. Burns states the law simply: "Every change takes place
at the cost of a certain amount of available energy." He adds that the
second law lends itself to the deduction that the cause of all change is the
26 RELATION OF COOKERY TO COLLOID CHEMISTRY
tendency of energy to attain the same uniform degree of intensity as that
of its environment. This means that any system tends to change to the
most stable state.
Page 25
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
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somewhat larger stresses. Plasticity is thus a complex property, made up
of two independent factors, which we must evaluate separately." Modeling
clay is plastic. Plasticity is an important property of fats used for cakes,
biscuits, and pastry. A plastic fat has a consistency such that it will form
a thin sheet or layer in a batter or it will retain air bubbles when
''creamed." The enclosing of these air bubbles in the fat is an aid in leaven-
ing cakes and may assist in obtaining a velvety texture, for the enclosing
of the air renders the fat more plastic, thus more easily distributed in the
batter at lower temperatures.
Energetics
Burns states, "Energy is the underlying cause of all changes in matter.
This does not seem a very satisfactory definition, but, so far, it is the only
one possible. . . . Energy, then, is that which produces an effect on our
senses." It is measured by its power to do work.
Energy in some form is often applied to the materials used for food
products. This energy may be electrical, mechanical, or in the form of heat.
An electric current passed through a food may be used to cook it. Very
interesting experiments are being carried out along this line of work by the
Household Equipment Department at Iowa State College. One of the
striking results is the very short time required to cook the food. The pas-
sage of an electric current is used by some companies to pasteurize milk
and by some to sterilize fruit juices.
Mechanical energy is used to beat, stir, fold, knead, or grind food.
The frequency of application of heat to foods does not need to be men-
tioned, for this is what the term to cook means. Foods may be cooked by
radiant heat; or by transmission of the heat by conduction, i.e., from parti-
cle to particle ; or by convection, which is the diffusion of heat through a gas
or liquid by movement of the gas or liquid particles. A combination of these
methods may be used to transmit the heat. Oven cooking employs all three.
Kinetic energy is due to motion. It may be due to motion of the sub-
stance itself or of the particles composing it. It is directly available for
work. Potential energy is associated with position, i.e., composition, stress,
or strain. Kinetic energy is necessary to liberate it to perform work.
Just as matter is indestructible, though its form may be changed, so is
energy indestructible. This constitutes the first law of thermodynamics.
The law of Hess states that the amount of heat generated by a chemical
reaction is the same whether it takes place all at once or in steps.
The second law of thermodynamics concerns the degradation or dissipa-
tion of energy. In practise, some of the freed energy is converted into heat,
which is diffused among the surrounding objects, and, so far as work is
concerned, is lost. Burns states the law simply: "Every change takes place
at the cost of a certain amount of available energy." He adds that the
second law lends itself to the deduction that the cause of all change is the
26 RELATION OF COOKERY TO COLLOID CHEMISTRY
tendency of energy to attain the same uniform degree of intensity as that
of its environment. This means that any system tends to change to the
most stable state.