Transcript Phase Transition: Changing Food with the Application of Heat

CHANGING FOOD WITH THE
APPLICATION OF HEAT
UNCOOKED
COOKED
TEMPERATURE
AN EXAMPLE OF A VERY SIMPLE PHASE DIAGRAM FOR
COOKING FOOD
PHASE DIAGRAM OF WATER:
SOLID
LIQUID
GAS
TEMPERATURE
0°C
100°C
PHASE DIAGRAM DESCRIBES THE TRANSITION FROM ONE
STATE TO ANOTHER WITH THE APPLICATION OF HEAT
SOME OTHER EXAMPLES OF SIMPLE
PHASE TRANSITION
NITROGEN:
SOLID
LIQUID
-210°C
ETHENOL:
SOLID
LIQUID
GAS
TEMPERATURE
78°C
GAS
-80°C
TEMPERATURE
-195°C
-114°C
CO2:
SOLID
GAS
TEMPERATURE
PHASE TRANSITION DIAGRAM OF AN
EGG
AN EGG GOING FROM LIQUID TO SOLID GOES THROUGH
MANY PHASE TRANSITIONS
Temperature
62°C
Ovotransferrin
unfolds
70°C
Yolk protein
unfolds
80°C
Ovalbumin
unfolds
It’s also true of other things
If you want to cook a turkey……….
texture and taste change as the
temperature increase
Bake a pie, or cake………..
Many different textures occur as the
temperature goes up.
What are we going to learn today?
Eggs, turkeys, pies, and cakes all have
complicated phase behavior.
1) Explain what those transitions are
2) Why they occur
3) How to control them
All to make you a better chef
PHASE CHANGE IN AN EGG AND
OTHER PROTIENS, AS WELL
Egg whites and yolks are composed of proteins in
liquid in their natural state.
Heat energy disrupts their molecular structure
causing one set of bonds to break and another
set to form.
This second bond creates a solid network
referred to as coagulation
The greater the temperature, the firmer the
coagulation
So, what’s going on?
A chain of amino acids
+
_
+ with peptide bonds
Folds back on itself to form a coil
Protein
+
Protein in muscle tissue is 20%, Fat 3% to
5%, and water 20%
Protein coils form muscle fibers (thickness of human hair)
Muscle fibers organize into muscle bundles
Muscle bundles are connected together with connective tissue
Water fills the spaces between the muscle fibers. Fat cells intersperse
themselves in the muscle bundles. All bound together with connective
tissue, a kind of living glue
Back to our egg
Egg proteins begin as folded chains of
amino acids
Heat up the water
As the proteins heat up, they begin to
uncoil (denature)
The higher the temperature gets, the more
proteins denature
When an egg is mixed with other liquids
Milk-fat globules
Proteins in an egg
Ovalbumin
Ovatransferrin
Ovomucoid
54%
12%
11%
80°C (180°F)
62°C (143°F)
70°C (158°F)
Proteins in egg yolk: 43%
Lipovitellin, Phosvitins
Fully set at
64.5°C (148°F)
70°C (158°F)
Custard set point:
Completely set by:
78°- 80°C (175°-180°)
85°C (185°F)
Critical temperatures inside an egg
Arrival of the emersion circulator. Perhaps, the most important
revolution in cooking.
All in a 13°C window!!
57°C (135°F) for 1 hour is a pasteurized egg
60°C (140°F) egg is barely set
62°C (143.6°F) white is set, yolk is runny, perfect for eggs benedict
63°C (145.4°F) white is firm, yolk is not fully set
64°C (147.2°F) yolk is fully set, yet soft and custardy
65°-66°C (149°-150.8°F) yolk is like play dough or marzipan
67°C (152.6°F) yolk is starting to become crystalline in nature
70°C (158°F) a perfect hard boiled egg with no sulfur aroma
COOKING PROTEINS IS A CHALLENGE
To cook Pasta, Grains,Vegetables, and Greens
Boil water and go!!
Meat and Fish, like eggs, have a complex protein structure as well
Applying heat to:
Disrupt
Unfold
Network
Different proteins get disrupted at different temperatures. Generally,
way below the boiling point of water
You get the best texture and flavor by partially completing this phase
transition, a tender, soft network
Too far and you get solid, tough, and hard
Bibliography
Harvard University of Applied Science and Engineering edX course on food
science
On Food and Cooking, the science and Lore of the kitchen. Harold McGee
Lipid-protein interactions in lipovitellin. Thompson, JR & Banaszak, LJ
The Nutritional Value of Egg White vs Egg Yolk, Grace Derocha