Modernist-Cuisine-Vol.-1-Small

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Celsius and Fahrenheit are the
most familiar temperature scales,
but many others exist. The Kelvin
scale uses the same size degrees as
Celsius but has a different starting
point: its 0 refers to absolute zero
(the lowest possible temperature)
rather than to the freezing point of
water. Kelvin is commonly used in
science to designate very low
temperatures.
Rankine is the Kelvin of the
Fahrenheit scale, although it has
never achieved the same popularity.
The Newton, Reaumur, and
Rømer scales are nearly obsolete,
although the Reaumur scale lives
on in relative obscurity in Italy,
where it is still used for making
Parmigiano-Reggiano cheese.
The rare Delisle scale has the
curious feature of assigning lower
numbers to hotter temperatures—
which is how the Celsius scale
worked until the 1740s, when
Anders Celsius died and Carl
Linnaeus flipped the scale around.
from the conversion of energy in some other
form, such as electricity (in the case of a coil
burner or induction element) or chemical bonds
(in the case of a gas burner or wood-fired oven).
Without a burner or some other source of
external energy to maintain the pan temperature,
heat will move from the pan to the steak until the
two have the same temperature. At that point they
are in equilibrium at some temperature between
the two starting points. A hot cup of coffee will
cool to room temperature (and not below it) only
because it doesn’t hold enough internal energy to
appreciably heat the room.
The rate at which heat flows from a hot pan to
a cold steak is proportional to the difference in
temperature between the twothe greater the
difference, the faster the flow of heat. Chefs
exploit this universal property of heat transfer
whenever they sear a steak on a really hot griddle
(see page 2·37).
Temperature difference is not the only factor
that can speed or slow heating, however. No doubt
you have noticed that some foods and cooking
utensils heat faster than others under similar
cooking conditions. Water’s apparent resistance to
heating, for example, spawned the aphorism “a
watched pot never boils.” To understand why, it
helps to know more about how different materials
respond to a change in internal energy.
A Capacity for Change
Materials vary in their reaction to heat. The
variations are caused by several factors. The size,
mass, complexity, and chemistry of the atoms and
molecules in the substance all play a role. Temperature
and pressure also can affect the amount of
energy required to raise the temperature of a
material by a certain amounta parameter that
scientists refer to as the specific heat capacity of
the substance. From the table on the next page you
can see that the specific heat of liquid water,
steam, and ice are all quite different. The form the
compound assumes matters, too.
Specific heat is expressed as the amount of
energy required to warm a given amount of mass by
a degree of temperature. For liquid water, this is
4,190 joules per kilogram-degree Celsius (abbreviated
4,190 J/kg · °C) or 1 BTU per pound-degree
Fahrenheit (1 BTU/lb · °F). So if you want to
increase the temperature of a kilogram of water
(that is, one liter) by a degree Celsius, just add
4,190 J of heat. Want to warm a kilo of ice by a 1 °C?
You’ll need only about half as much energy: 2,090 J.
Whereas a 1 °C / 1.8 °F rise in air temperature
under typical room conditions comes at a price of
just 1,012 J, the energetic cost for the same
THE PRO PERTIES OF
Resistance to Change
temperature increase in copper is just 390 J.
Tungsten, the metal found in light bulb filaments,
has one of the lowest specific heat capacities it
doesn’t take much heat at all to change the
temperature of tungsten.
At the other end of the range, hydrogen gas has
a specific heat more than 100 times as high as that
of tungsten. For as much energy as you’d need to
warm a gram of recalcitrant hydrogen gas by 1 °C
/ 1.8 °F, you could instead change the temperature
of a gram of tungsten by 108 °C / 194 °F.
Some of the common materials in the kitchen change temperature much more readily than
others. The specific heat capacity of a material describes how much heat we have to move into a
given amount of a material to raise its temperature by one degree. For the specific heat values of
other kitchen materials, see From Pan Bottom to Handle, page 280.
Specific heat capacity
Material (J/kg · °C) (BTU/lb · °F)
For more on the properties of food and
cookware that affect heat transfer, see
Conduction in Cookware, page 277.
aluminum 910 0.22
Want to eliminate hot spots in your skillet? Have a metal shop cut
a thick plate of solid aluminum for you, and place it between the
pan and the burner. A plate 1–3 cm / ½–1½ in thick will spread the
heat more evenly than the most expensive copper pans do.
copper 390 0.09
carbon steel 490 0.12
tungsten 132 0.03
glass plate 500 0.12
wood 1,700 0.41
corkboard 1,900 0.45
Styrofoam insulation 1,300 0.31
water (liquid) 4,190 1.00
water (vapor) 1,930 0.46
water (ice) 2,090 0.49
beef loin 2,760 0.66
apples 3,640 0.87
eggs 3,180 0.76
milk 3,770 0.90
air 1,012 0.24
hydrogen 14,320 3.40
nitrogen (gas) 1,040 0.25
nitrogen (liquid) 2,042 0.49
266 VOLUME 1 · HISTORY AND FUNDAMENTALS
HEAT AND E NERGY 267