Eggsperiments!
Part I: The Incredible, Edible Egg
Spice of Life Class 8, Fall 2012
Student Learning Goals:
After completing this session of Eggsperiments, students will be able to:
1. Describe the relationship between the structure and the function of a protein.
2. Discuss the various ways in which proteins can be denatured in the kitchen, and
the impact of denaturation on protein structure and function.
3. Describe the different biochemical components of the egg, and how cooking
impacts each of them.
4. Calculate the amount of time necessary to boil an egg to a desired level of
doneness, given a variety of egg sizes and water temperatures.
VI.
Proteins
A.
Amino Acids and Peptides
1.
Amino Acid Structure
2.
Protein Structure
3.
Protein Function
4.
Protein Denaturation
5.
Effect of Denaturation on Protein Structure and Function
Eggsperiments!
Now that you know about the scientific principles that underlie cooking by convection
and conduction, and how protein structure is affected by cooking, it is time to put all of
that hard-earned knowledge to practical use. That is, you will now learn how to make the
perfect boiled eggs. Before you can do that, however, we’ll need to take a look at egg
structure.
The Anatomy of an Egg
This fellow ought to look pretty familiar now,
but we need to talk just a bit more about the
biochemical composition of the yolk and the
white before we move on.
Biochemical Composition of the Egg Yolk:
Biochemical Composition of the Egg White:
Cooking an Egg:
In the book ‘The Science of Cooking”, Peter Barham derives the following formula for
cooking an egg initially at a temperature of T0, and with diameter of d mm:
Diameter, d
é 4(T - T ) ù
time = 0.0015d 2 lnê water 0 ú min
êë(Twater - Tyolk ) úû
In other words, the time it takes to boil an egg in water really depends on the volume of
the egg, the temperature of the egg, the temperature of the water, and the final
temperature you desire for your yolk. As you have now learned, that final temperature is
all-important, not only for safety, but also for taste, texture and appearance. The problem
with this formula is that it does not always seem to work…so let’s see how we do this
year!
Procedure:
1. Each group should get 2 eggs. Note that they have been stored on their sides (to
keep the yolk centered) and that they have been warmed to room temperature (to
help keep them from cracking).
2. Turn on your electric burners, and place water in your pot.
3. Take the temperature of the room, and convert it to °F
Formula: °C = (°F-32) x 0.56.
4. You will be using the table below for all of today’s cooking calculations, so go
ahead and convert all of the temperatures in the first column to °F, and write them
in the table below, and in the appropriate part of the Eggsperiments worksheet
that follows.
Temperature
Below 55°C
57°C
62- 63°C
62-65°C
65-70°C
73°C
77°C
80°C
90°C
Effects on Egg White
Effects on Yolk
Risk of Salmonella
Eggs held at this temperature for 75 minutes are
considered to be Pasteurized
Ovotransferrin begins to
‘Runny’ liquid
denature
Soft and gelatinous texture
Most egg white proteins
Egg yolks still runny
begin to denature
Set as a soft gel
Still runny, but liquid
starting to thicken – Most
egg yolk proteins begin to
denature at this
temperature
Hardening of white,
Soft, gel like texture rather
texture of soft fruit,
like a thick shampoo
strawberries, etc.
White continues to harden Hard-boiled still soft, but
solid texture of set yoghurt
Ovalbumin denatures
Onset of green
discoloration around edge
of yolk
Overcooked tough white,
Yolk completely dry,
texture of damp sponge
crumbly solid, quite a bit
of green
5. Measure the diameter of each of your eggs. Record the values in the
Eggsperiements table in the worksheet.
6. You will initially be hard-boiling your eggs. A hard-boiled egg’s yolk has
reached 73-77°C all the way to the center, but has not yet turned green! Calculate
the time that this will take for each egg and record the value in the Eggsperiments
table.
7. When the water has reached 100°C (212°F), place one egg into the pot. Try to
monitor the boiling so that it is not too vigorous, but does remain at 212°F/100°C.
Cook the egg for the amount of time that you calculate, then place it quickly into
cold water. This keeps it from cooking any further, and makes the egg easier to
peel.
8. Cool the egg for 10 minutes.
9. Carefully remove the shell from your hard-boiled eggs and observe them. Did
they cook as you expected? Enter the answer in the Eggsperiments worksheet.
10. If so: then go ahead and try to make a soft-boiled egg, or see if you can make the
egg green. Write the appropriate ‘style’ (green, soft-boiled, etc) in the table, show
your calculations in the worksheet, and then cook the egg.
If not: then try again, adjusting the timing. Write ‘hard-boiled’ in the space in the
table, and give the new cooking time (calculations not needed).
Recipe for Deviled Eggs