Eggsperiments! Energy Transfer, Protein Structure, Eggs and… Cheesecakes!

Spice of Life Class 8, Spring 2012

Introduction:

Custards are sweet or savory foods that use egg yolk proteins as the thickening agent in a gel. The liquid in many custards is milk (which, of course, brings additional proteins, fats and emulsifiers to the mix). Cheesecakes are particularly interesting custards because they also use something called the ‘creaming method,’ which adds even more ‘thickness’ to the custard - in the form of bubbles. Before you make your cheesecakes, however, you’ll need to understand quite a bit more about how the custard forms and how the oven, pan and fluid in which the cheesecakes cook will all influence their ultimate consistency.

Student Learning Goals:

As a result of completing this session of Eggsperiments, students will be able to:

A. Understand the science underlying cheesecake consistency.B. Understand how each ingredient in the cheesecake contributes to that

consistency.C. Be able to articulate how the ability to transfer heat varies with the

composition of baking pans, and how that ability affects baked foods (particularly cheesecakes).

D. Be able to articulate how the specific heat of water helps to ensure that cheesecakes do not over-coagulate.

E. Make a pretty darn delicious cheesecake.

A. The Science of Heating and Cooking Cheesecakes

I. OverviewA. Heat and TemperatureB. Methods of Heat TransferC. Applications to Cookery

II. Heat and TemperatureA. General Considerations

B. Latent Heat

C. Heat Flow

III. Methods of Heat Transfer

A. General Considerations

B. Conduction: Direct Contact

C. Convection: Movement in Fluids

D. Radiation: Pure Energy of Radiant Heat and Microwaves

IV. The Science of Sauces and Custards

“Confidence is going after Moby Dick in a rowboat and taking the tartar sauce with you.”

~Zig Ziglar quotes

A. Sauces

a. What is a Sauce?i. General Concepts

ii. Viscosity

iii. Thixotrophy

b. How Do Sauces Thicken?i. Thickening Agents

1. Starches

2. Fats (Emulsions)

3. Proteins

4. Carbohydrate Jellies

5. Bubbles and Foams

B. Custards

a. What is a Custard?

b. Some Examples of Custardsi. Flan

ii. Ice Cream

iii. Pudding

iv. Quiche

The Recipe:

INGREDIENTS:1 ¼ cups Honey Maid Graham Cracker Crumbs¼ cup butter, meltedThree 8-oz. bricks of cream cheese at room temperature½ cup sugar2 Tablespoons flour1 Tablespoon vanilla2 large eggs3 large egg yolks5 oz sweetened, condensed milk1 cup sour cream

DIRECTIONS:1) Preheat the oven to 250°F and bring a quart of water to boil.2) Spray muffin tins with cooking spray.3) Mix the crumbs with the butter.4) Press the crumbs into the bottom of the muffin cups, and up the sides to form a

crust.5) Place the cream cheese, sugar and flour in a large metal mixing bowl, and beat on

medium speed until completely smooth and creamy, scraping down any stray bits with a spatula, and trying to avoid allowing the cream cheese to “reach exit velocity and attempt to leave the bowl” (Alton Brown).

6) In a separate bowl, whisk together the vanilla, eggs, egg yolks, condensed milk and sour cream.

7) Turn the mixer down to low power and very slowly drizzle the egg mixture into the cream cheese mixture, again avoiding exit velocity and occasionally scraping down the sides of the bowl to ensure complete mixing.

8) Pour the cream cheese filling into the prepared muffin tins.9) Place the muffin tins into baking dishes, fill the baking dish with boiling water,

and place the whole set up in the oven for one hour.10)Turn off the oven and open the door to look (quickly) at the cheesecakes.11)Close the door and let the cheesecakes sit for another hour in the hot oven.12)Remove the cheesecakes from the oven, and let cool to room temperature for 1

hour.13)Cover the cheesecakes and place them into the refrigerator until class on Friday

morning, when we will ‘analyze’ them and complete the remaining portion of the worksheets.

Eggsperiments! Worksheet, Part II: Cheesecakes

Names

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1. Make a series of related hypotheses that predict the impact that the following independent variables will have on your cheesecake recipes. Be sure to discuss how you expect the size of the oven and the composition of the pan to impact variables such as heat transfer, convection, radiant heat, etc., and then describe how you expect each cheese cake batch to cook (faster, slower, more or less browning of the crust, etc?) with relation to the other batches in light of these variables.

a. Small oven, silicone muffin pan

b. Large oven, silicone muffin pan

c. Small oven, dark metal muffin pan

d. Large oven, shiny metal muffin pan

2. Cheesecakes often crack as they are cooked. This cracking is due to overcooking the eggs – which literally become hard-boiled, and then become rubbery and dry. Going back to your ‘Eggsperiments’ handouts, and your class notes on water, answer the following questions:

a. At what temperature do egg whites become rubbery, and egg yolks become completely dry and crumbly?

b. At what temperature are you cooking your cheesecake, and why is this potentially a problem?

c. What role do you think the boiling water in your pan is playing in assuring that the eggs in your recipe do not become rubbery, dry and crumbly?

3. What roles do the following ingredients/recipe steps have on the final cheesecake consistency?

a. Beating the cream cheese

b. Sugar

c. Flour

d. Cooked eggs

e. Emulsifiers (name two present in this recipe)

f. Cooking at relatively low heat for a long time (250°F maximum) instead of at 350°F for a short time.

4. What impact did the following independent variables will have on your cheesecake recipes? Where your predictions correct? If not, what are some variables that you did not consider in your initial answers that could have played a role in the final outcome?

a. Small oven, silicone muffin pan

b. Large oven, silicone muffin pan

c. Small oven, dark metal muffin pan

d. Large oven, shiny metal muffin pan