What A Yolk!

                I was curious as to see how egg yolk worked within baking cookies. I wanted to see if taking out the egg yolk and just using egg whites would make a difference. Egg yolk has a lot of emulsifiers in it which help bind the ingredients together. I was curious if I took out the egg yolk, would the cookie stay together or would it spread out even more because there were less emulsifiers?

My hypothesis is: If I bake two separate batches of cookies, one with one egg and the other with just one egg white, then the batch of cookies with the egg whites will be greater in diameter than those with the regular egg. My independent variable is taking out the egg yolk in one of the batches and just using egg whites. The dependent variable is the size of the cookie in inches.  I made this experiment controlled by using the same oven, the same cookie mix, the same amount of butter, the same size spoon to place the cookie dough on the pan, and both batches were baked in the same amount of time.

Results:  The batch of cookies that had the regular eggs were larger in size than the batch of cookies that only had egg whites. Cookie with egg yolk 1 was 4.5 inches, cookie with egg yolk 2 was 4.1 inches, and cookie with egg yolk 3 was 4.2 inches. Cookie with egg white 1 was 3 inches, cookie with egg white 2 was 3.6 inches, and cookie with egg white 3 was 3.1 inches.

These were the cookies that had the regular egg in them! (Below)

These were the cookies that had only the egg white! (Below)

 The cookies on the left are the ones with only egg whites and to the right are the cookies with the regular eggs. (Below) 

In an ideal world, I would use something to make sure the cookie dough placed on the pan were all the exact same size before baking. I would also use an oven with convection bake so I didn’t have to flip around the pans. To better my experiment, I would make about 10 batches of each, 10 with egg yolk and 10 without egg yolk. This would give me a better idea if the egg whites really do affect the cookies and get a more precise number of the difference of the diameter.

Betty Crocker Chocolate Chip Oatmeal cookies were the cookies I made. For the first batch, I used one stick of margarine (melted), one egg, and the pre-made Betty Crocker Chocolate Chip Oatmeal mix. For the second batch, I used one stick of margarine (melted), one egg white, and the pre-made Betty Crocker Chocolate Chip Oatmeal mix. I melted the margarine in the microwave and poured that into a medium mixing bowl. I poured the pre-made mix in the mixing bowl. Then, I cracked one regular egg into the bowl. I mixed the stirred until all of the ingredients were mixed. I took a regular table spoon and scooped out several globs of the cookie dough and put it onto a pam sprayed pan. For the second batch, I did everything the exact same, except I took out the egg yolk and just used egg whites. I used the step-by-step directions on the back of the Betty Crocker pre-made package.

Overall, I rejected my original hypothesis. Cookies with egg whites seem to be smaller than cookies with the yolk and the egg white. I was surprised but also fascinated and am curious to do more research and find out why this happened! 

This is a graph of the results. The diameter (inches) of the cookies is on the Y Axis and the number of the cookie is on the X Axis. The blue bars are the cookies with the regular egg and the red bars are the cookies with just the egg whites.