The Chemistry of Cooking:
Why
Chemists
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Chefs
How
knowingMake
chemistry
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Dr. Nancy Mills
Murchison Professor of Chemistry
Trinity University
Texas A & M University
First Year Chemistry Program Seminar Series
References
On Food and Cooking: The Science
and Lore of the Kitchen; Harold
McGee, 2004, Scribner and Sons,
New York.
Cooks’ Illustrated: The Science of
Good Cooking; 2012, America’s
Test Kitchen, Brookline, Ma
The Curious Cook, More Kitchen Science and Lore; Harold McGee,1990, McMillan, New
York.
How to Read a French Fry, and Other Stories of Intriguing Kitchen Science; Russ
Parsons, 2003, Houghton Mifflin, New York.
What Einstein Told His Cook, Kitchen Science Explained; Robert L. Wolke, 2008, W. W.
Norton, New York
Perfect Hard Boiled Eggs
1 or more eggs at room temperature
Enough water to cover the eggs
Cover the egg(s) with cold water and bring to a boil.
Immediately turn off the heat and leave the egg for
10 minutes, then remove.
What’s with the greenish ring?
Egg whites contain cysteine and
methionine:
Egg yolks contain
iron, Fe
Together they
form greenish FeS,
ferrous sulfide
The cure: plunge into ice cold water when cooking is done.
Egg miracles
Egg whites: mostly water, 10% proteins with negative
charges
Meringues:
beat whites until they form stiff peaks
mix in a copper or ceramic bowl
add a little cream of tartar or sugar at end
Egg Miracles II
Yolks: 50% water, 34% fats including lecithin
and cholesterol, 16% protein
(think detergent)
NH3
Emulsified sauces:
Lecithinsuspension of liquids in
liquids, e.g.:
mayonnaise and Hollandaise sauce
Mayonnaise
Mix egg yolk and lemon juice together
beat in oil slowly
Hollandaise sauce
Beat egg yolks,
then add water, lemon juice, salt
Heat and stir until creamy
Add butter: a) remove from heat and add
melted butter
Or b) add small chunks of solid butter, stir
until melted.
One tablespoon
¼ cup
3/8
cup
oiloil of oil
½ cup oil
Speaking of sauces:
Starch based sauces: sols, dispersion
of solid material in liquid
Amylose: a long chain that can
get tangled to give some
structure
Amylopectin: highly branched,
more compact, doesn’t thicken
as well
Multifaceted role of flour
Contains starch: used to thicken sauces
Starch in cold water: Water can’t
penetrate the starch granule
With heat, the water has enough
energy to penetrate
Other types of starch: cornstarch, arrowroot
Dissolve in water, add to hot liquid with stirring, heat to
boiling
Gravy, the bane of a cook’s existence
Gravy or white sauce:
Mix flour with oil, fat, or butter in equal
amounts and cook for 1 minute. Remove from
heat, add appropriate amount of liquid for type
of sauce desired, heat to boiling
Chemist’s tools for cooking
Separatory funnel
Fat separator
Why do meats brown when they are
cooked? The Maillard reaction!
The amino acids react with sugars to make N-substituted
glycosamines,
Bread crust-y
floral
Oniony, meaty
Chocolate, earthy
Browning depends on temperature!
Flour in breads and cakes
Flour is mostly starch (70%) but the 10% which are proteins are the structural
elements of bread
Gliadins have intra-molecular
disulfide linkage while glutenins
have both inter- and intramolecular disulfide linkages.
gliadins are compact and globular
glutenins are linear and have
relatively higher molecular weight
Why is bread dough elastic? Glutenin
High protein flour, has the most gluten, used for bread
Cake flour and pastry flour: from soft wheats, less protein, more starch
Peggie Mills’ White Bread
Combine ½ cup sugar; 4 t salt; 1 T oil; 1 T butter; 21/2 cup boiling water. Allow to cool
until lukewarm.
Dissolve 2 pk yeast in scant ½ cup lukewarm water. Add to above mixture. Stir in 6 cups
flour. Turn onto floured surface, knead until moist but not sticky.
Let dough rise in an oiled bowl until doubled in size. Make into three loaves. Let rise
again. Bake at 350º for 25 minutes or until browned on top.
What happens with kneading?
Kneading organizes the gluten
proteins into networks to increase
strength.
Green Beans with Rosemary
2 pounds green beans, trimmed
¼ cup butter
1 T chopped fresh rosemary (or more)
Blanch green beans. Drain and pat dry. Set aside.
Melt butter in a large skillet over medium high heat
until frothy, stir in rosemary, and sauté for 3-5
minutes. Add green beans, toss to coat, and heat until
the beans are warm.
Cooking vegetables
Green vegetables have chlorophyll; blanching causes a sudden
expansion of gases trapped in the spaces between cells, which
obscure color.
Bright green, soluble in fats
Soluble in water
Dull olive-green
Heating herbs with butter causes the volatile compounds from
herbs to be extracted.
Poached/Steamed Salmon with Dill
Sauce
2 tablespoons butter
1 teaspoon lemon
1 pound fish fillets (or steaks)
1. Place butter and lemon juice in a 10 x 6 baking dish.
Microwave on high for 30-45 seconds until butter is
melted.
2. Add fish, thickest end toward outside, in dish,
season with salt and pepper, cover with plastic
wrap.
3. Microwave on high for 6-8 minutes or until fish
flakes easily. Turn fish midway through.
Miscellaneous Cooking Issues
More tips about cooking vegetables
Why should meat rest after cooking?
Why does brining a turkey make it juicier?
Why use kosher salt?
When should you salt and pepper your cooking food?
Fudge
3 ounces unsweetened chocolate, coarsely chopped (3 1-ounce
squares)
3 cups sugar
1 cup half-and-half
1 tablespoon corn syrup
1/4 teaspoon salt
3 tablespoons butter
2 teaspoons vanilla extract
Grease an 8" square pan with butter. Mix together chocolate,
sugar, half-and-half, corn syrup, and salt in the saucepan. Stir over
medium-low heat with a wooden spoon until the chocolate melts
and the mixture begins to boil. As soon as the syrup starts to boil,
stop stirring and clip the candy thermometer to the side of the
saucepan, being careful not to let it touch the bottom. Let the
syrup cook, undisturbed, until it reaches the soft-ball stage,
about 235° F–240° F.
Fudge (continued)
While it cooks, wash down the sides of the saucepan with a
pastry brush dipped in a small amount of warm water to loosen
and dissolve any sugar crystals clinging to the sides. Remove the
saucepan from the heat and let the mixture rest, undisturbed.
Let it cool to approximately 110° F. Add the vanilla and butter
and begin to stir with a wooden spoon. Stir constantly until the
fudge “sets up.” Pour the mixture into the prepared pan.
Thanks!
Any questions?
Chocolate Almond Fudge
1 cup milk
2 sqs (2oz) unsweetend chocolate
2cups sugar
1 tablespoon corn syrup
1/16 teaspoon cream of tartar
2 ½ tablespoons butter, cut up
1 teaspoon almond extract
Cut up the chocolate and add it to the milk in a heavy sauce pan or kettle. Heat slowly
stirring constantly, until the chocolate is dissolved. Mix in the sugar, corn syrup, and cream
of tartar, and stir until the sugar has dissolved and mixture is smooth. Using a damp pastry
brush, wash any remaining sugar crystals down from the sides of the pan.
Chocolate Almond Fudge (cont)
Cook, uncovered, stirring occasionally with a wooden spoon until a candy thermometer
reads 238°F or 26° above normal boiling point.
Remove the pan from the heat, add the butter without stirring and let the mixture cool.
When it is lukewarm, add the almond extratct and beat the mixture until it thickens.
Without scraping the sides of the pan, pour the mixture into a greased 9-inch square pan
and score it in squares. Cool thoroughly in the refrigerator.
If the fudge refuses to harden, warm it in hot water, return it to the saucepan with a few
tablespoons water and bring it slowly up to boiling again. When it reaches the
appropriate temperature, proceed as in the preceding paragraph.
Where does chemistry play a role?
•
•
•
•
Taste, of course
Appearance of food
Smell of food
Structure of food
What about cakes?
Structural agent is starch, not gluten, so we surround it
with water and heat it up; batters clearly have much more
water. Second structural element is egg.
Leavening agents: baking soda, NaHCO3, but needs some
source of acid
H+ + HCO32-
H2CO3
H2O + CO2
Acids? Buttermilk, yogurt, lemon juice, molasses, brown sugar
Or use baking powder:
Alchemist’s Menu
Steamed artichokes with Hollandaise Sauce
Poached Salmon with Dill Sauce
Green beans with Rosemary
Bread
Chocolate Almond Fudge
Steamed Artichokes with Hollandaise
Sauce
Why steam?
Cooking vegetables, a side trip:
What does heating do?
What about adding acid (lemon juice or vinegar) or a base (baking soda)?
Lemon Dill Sauce
3/4 cup dry white wine
3 tablespoons chopped shallot
2 tablespoons fresh lemon juice
1/2 cup (1 stick) chilled unsalted butter, cut into 8
pieces
1 1/2 tablespoons chopped fresh dill
Boil wine, shallot and lemon juice in medium
saucepan over high heat until reduced to 1/4 cup,
about 6 minutes. Reduce heat to low; add butter, 1
piece at a time, whisking until melted before adding
more. Remove pan from heat. Stir in dill. Season to
taste with salt and pepper.