Modernist-Cuisine-Vol.-1-Small

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For more on distance effects in broiling and
grilling, see page 2·14.
Entering a New Phase
Conduction, convection, and radiation are the
classic modes of heat transfer described in every
textbook. But there’s another, largely unsung,
form of heating that plays a big part in cooking:
the thermal energy that comes from melting or
freezing, evaporation or condensation. These
transitions of matter among its principle states
solid, liquid, and gasare called phase changes.
Whenever such a change occurs, the substance
releases or absorbs a considerable amount of
thermal energy that can be used to warm food or
to cool it.
In the kitchen, steaming offers the most common
example of heat transfer by phase change.
Water consumes a tremendous amount of thermal
energy when it boils off to steam. You can imagine
the water vapor taking that energy along with it as
a kind of latent heat. In fact, that’s what physicists
call it: the latent heat of vaporization.
The vegetables in a steamer basket don’t cook
because they’re surrounded by piping-hot steam;
it’s the latent heat released when steam condenses
to liquid water on the cooler surface of the vegetables
that does the cooking. Subtle changes in how
steam condenses on food can have such surprising
effects on the speed of steaming that in many
cases it is, counterintuitively, a slower way to cook
than boiling is (see Why Steaming Is Often Slower
Than Boiling, page 2·72).
Blowing on food is an example of how phase
transitions can also cool food by hastening the
evaporation of water and other liquids (see Why
We Blow on Hot Food, page 288). In vacuum
assisted cooling, lowering the pressure makes
evaporation occur more quickly, and the transition
consumes so much heat that you can freeze food
this way. The fog that emanates from liquid
nitrogen or dry ice also signals an energydevouring
shift from liquid to vapor. Any food
that comes in contact with this maelstrom will
have the heat sucked right out of it.
The next chapter discusses phase transitions in
more detail. The point here is that the large
quantity of energy involved in matter’s shift from
one state to another offer a powerful resource for
rapidly heating and cooling food; it can have an
astonishing impact on culinary techniques, for
better and for worse. To manage these effects, it
helps to understand the most versatile and abundant
constituent of food, and the only one you can
find as a solid, liquid, and gas in nearly any working
kitchen: namely, water.
Further Reading
Atkins, Peter W. The 2nd Law: Energy, Chaos, and
Form. W. H. Freeman, 1994.
Atkins, Peter W., et al. Chemistry: Principles and
Applications. Longman, 1988.
Incropera, Frank P. Fundamentals of Heat and
Mass Transfer. Wiley, 2006.
Lewis, Christopher J.T. Heat and Thermodynamics:
A Historical Perspective. Greenwood, 2007.
Von Baeyer, Hans C. Warmth Disperses and Time
Passes: The History of Heat. Modern Library, 1999.
THE PHYSICS OF
When Color Indicates Temperature—and When It Doesn’t
All objects change color as they heat from very low temperatures
to very high ones. That is what is meant by the term
“color temperature,” which is used in photography and even
in rating fluorescent bulbs.
But temperature is just one of the properties that can
determine the spectrum of light an object radiates. Some
colors are only incidentally related to temperature. The blue
flame of a gas burner is a good example; so is the yelloworange
aura of a sodium streetlamp.
These colors are determined by the so-called emission
spectra that arise during the combustion of elements. Emission
spectra are bursts of colored light that issue from heated
Methane
(natural gas)
Calcium sulfate
dihydrate
(gypsum)
Calcium phosphate
(bone / tooth
enamal)
atoms as their electrons bounce from a high-energy state to
a lower-energy ground state. Each element in the periodic
table has a characteristic emission spectrum recorded in
carefully controlled experiments.
Some differences are obvious to the naked eye, however.
You can easily distinguish the yellow-orange sodium
streetlight from a blue-green mercury-vapor lamp. One
isn’t substantially hotter than the other; their different
colors simply indicate the presence of elements with
different emission spectra. Likewise, the blue flame on the
stove top signals the combustion of hydrocarbons in natural
gas or propane.
Sodium chloride
(table salt)
Potassium
phosphate
(brining salt)
Sodium borate
(Borax)
290 VOLUME 1 · HISTORY AND FUNDAMENTALS
HEAT AND E NERGY 291